Kumhos

[ek1]

After suffering compound delamination on my front tires AGAIN a day and a half into my 2-day track weekend at the Glen, I got too excited after seeing some ad for a Kumho tire rebates on Tire Rack. After reading their web site, of course the ACR tires are not eligible :furious:

Out of despair, I started reading reviews of a regular (non-ACR specific) Ecsta V720. And guess what? Out of 32 reviews, literally every other one states that these tires are delaminating during autocross/track driving. Some people also experienced blistering and chunking (and so did I). Check it out: https://www.tirerack.com/tires/tires.jsp?tireMake=Kumho&tireModel=Ecsta+V720#RatingsReviews

So frustrating......$700 in tires per weekend. And that's taking it easy. I think my fastest lap there was 1.23.xx and I made it a point not to drive for more than 20 min per session and 4 sessions per day.

I've had it. I'm putting Hoosiers on the front for the next track event.

[ACRSNK]

Damn...that can get expensive.

[DZnutz]

Have you contacted Kumho with photos and details?

[ek1]

Have you contacted Kumho with photos and details?

Why? It's not like they are going to keep replacing my tires for free. I already read several reviews that said they contacted Kumho about these tires falling apart and got zero results.

[sadil]

Damn, that is nuts. What kind of wear do you expect on the Hoosier's? What is "benchmark" wear for driving 9/10ths to 10/10ths.

[ACRucrazy]

After suffering compound delamination on my front tires AGAIN a day and a half into my 2-day track weekend at the Glen, I got too excited after seeing some ad for a Kumho tire rebates on Tire Rack. After reading their web site, of course the ACR tires are not eligible :furious:

Out of despair, I started reading reviews of a regular (non-ACR specific) Ecsta V720. And guess what? Out of 32 reviews, literally every other one states that these tires are delaminating during autocross/track driving. Some people also experienced blistering and chunking (and so did I). Check it out: https://www.tirerack.com/tires/tires.jsp?tireMake=Kumho&tireModel=Ecsta+V720#RatingsReviews

So frustrating......$700 in tires per weekend. And that's taking it easy. I think my fastest lap there was 1.23.xx and I made it a point not to drive for more than 20 min per session and 4 sessions per day.

I've had it. I'm putting Hoosiers on the front for the next track event.

Dodge/Mopar was just running a buy 3 get 4th tire free deal. The Kumhos at the dealer qualified I believe.

[Rare Snake]

Dodge/Mopar was just running a buy 3 get 4th tire free deal. The Kumhos at the dealer qualified I believe.

I don't know if it's different in the U.S. but up here it only applies up to 18" tires I believe. In all honesty, that's not even that great of a deal.

[IndyRon]

I don't know if it's different in the U.S. but up here it only applies up to 18" tires I believe. In all honesty, that's not even that great of a deal.

If the 4th tire free is a Rear one, its a very good deal.

[Rare Snake]

If the 4th tire free is a Rear one, its a very good deal.
Very true LOL

[ek1]

Damn, that is nuts. What kind of wear do you expect on the Hoosier's? What is "benchmark" wear for driving 9/10ths to 10/10ths.

At this point the only thing I expect from Hoosiers is not to be worse than Kumhos, which is - I want to be able to get more than 2 track days out of them. Of course, if it rains, my track day will be mostly over since Hoosiers and standing water dont mix.

I dont know what the benchmark wear is for driving 9/10ths or 10/10ths. I think some forum members here do that and they can chime in, but I remember reading posts that mirror my experience - 1-2 track days max out of set of fronts. I personally always drive at 7/10ths since I dont want to run out of talent.

[DZnutz]

Why? It's not like they are going to keep replacing my tires for free. I already read several reviews that said they contacted Kumho about these tires falling apart and got zero results.

Seems like the most logical course of action. I dont care what someone, somewhere on some online thread posts. I would go to the source and get a resolution. Some people simply like to complain but not really accomplish anything

[ek1]

I agree with you, but I already have a full time job and a family, so at this point my time is more valuable than spending days on the phone with someone at Kumho, trying to convince them that their tires are shit. They already know, but will never admit it because if they do, they will incur multi-million dollar losses from having to replace delaminating tires. So I won't complain. I'll just vote with my wallet and use another brand of tires.

The goal of my post was just a warning to anyone who is considering an ACR-E as a track car.

[sadil]

I agree with you, but I already have a full time job and a family, so at this point my time is more valuable than spending days on the phone with someone at Kumho, trying to convince them that their tires are shit. They already know, but will never admit it because if they do, they will incur multi-million dollar losses from having to replace delaminating tires. So I won't complain. I'll just vote with my wallet and use another brand of tires.

The goal of my post was just a warning to anyone who is considering an ACR-E as a track car.

Thanks for the input. I totally agree. At this point, the Kumho tire being chewed up on the track quickly is well documented. For ACR owners, the first set will really determine if your going to be using the tire throughout the life of the car. Looking forward to seeing your impressions after switching to the Hoosier. I still would love to have one rear tire to hang in the garage that says "ACR". I think that's super cool!

[RedTanRT/10]

ek1, saw this thread and the other you posted. Those factory Kuhmo's seem like a great qualifying tire to set lap records for a street tire, but all I ever see and read is that their track life is ridiculously short.

I've run Hoosiers on my G3, G4 and now Comp Coupe and never have seen these type of issues. Viper front's wear twice as fast as the rear's, but I've never seen Hoosiers come apart like this.

IMO, if your gonna track a G5 ACR, go with an 18 set up all around and run with A7's or R7's. Keep the Kumho's for the street

[Dman]

Isn't there an 18" wheel option out now for tire options?

Now that I'm in an ACR, and starting events, this is going to be an issue for me, no question.

[ek1]

ek1, saw this thread and the other you posted. Those factory Kuhmo's seem like a great qualifying tire to set lap records for a street tire, but all I ever see and read is that their track life is ridiculously short.

I've run Hoosiers on my G3, G4 and now Comp Coupe and never have seen these type of issues. Viper front's wear twice as fast as the rear's, but I've never seen Hoosiers come apart like this.

IMO, if your gonna track a G5 ACR, go with an 18 set up all around and run with A7's or R7's. Keep the Kumho's for the street

I am afraid of running 18's because of so little clearance between the caliper and the rim. Even with my stock wheels, my calipers have scratches from shit stuck between them and the rim. Plus, believe it or not, I _STILL_ have the original rear tires from the factory mounted on the car and they are still good for a few more track days at least. So it's just the front tires that are a problem.

I already bought a set of stock 19" front rims and mounted 295/30/19 R7s on them last year, just did not get a chance to use them. But now since I am already doing another wheel alignment, I'll put them on. I will be creating a separate thread for recommended height/camber/pressure settings for them.

[RedTanRT/10]

Isn't there an 18" wheel option out now for tire options?

Now that I'm in an ACR, and starting events, this is going to be an issue for me, no question.

Dman, I see a guy from LA at Dan Cragin's shop that has a CCW 18 set up. Might be other choices too? Seems like there are thread's on this board discussing.

But, as ek1 points out, seems like with 18's there is a very tight clearance and folks get concerned about about wayward rocks/pebbles getting lodged between the wheel and caliper

[ek1]

Isn't there an 18" wheel option out now for tire options?

Now that I'm in an ACR, and starting events, this is going to be an issue for me, no question.

There are several options out there (I have all those threads bookmarked, will post later tonight), but clearance between the ACR CCB caliper and the 18" rim is literally a few millimeters. If a hard object were to jam itself in there at high speed....well...who knows what will happen, but one thing for sure - it will be expensive as hell to fix. From what I recall, there are also tire rubbing issues at full compression with some configurations. That's why I have been holding off on 18's. It's also a one-way street in a way that you can't just take 18's off and throw stock wheels back on without redoing the wheel alignment, which is again....expensive. Then there is corner balancing that has to be redone (expensive).

Good luck with tracking your ACR. You are not going to believe how much fun it is. But open your wallet really, REALLY wide.

[PkB2014]

What's the point in 18" all around since A7/R7 come in stock G5 sizes already? Seems unnecessary. I was planning to just get another set of wheels in stock sizes and put some Hoosiers on them for when I want do AutoX or Track days.

Also, the Demon tires (NT05r) doesn't come in 18" for the viper but does come in stock wheel sizes. If someone were interested in drag radials.

[ek1]

What's the point in 18" all around since A7/R7 come in stock G5 sizes already? Seems unnecessary. I was planning to just get another set of wheels in stock sizes and put some Hoosiers on them for when I want do AutoX or Track days.

Also, the Demon tires (NT05r) doesn't come in 18" for the viper but does come in stock wheel sizes. If someone were interested in drag radials.

We are taking about ACR tires and stock rear for the ACR is 355/30/19. As far as I know, Hoosier does not make R7 or A7 in that size. Tire Rack now has Pirelli pZero Corsa in 355/30/19 for a small price of $640 _PER_TIRE. Fok that!

[PkB2014]

We are taking about ACR tires and stock rear for the ACR is 355/30/19. As far as I know, Hoosier does not make R7 or A7 in that size. Tire Rack now has Pirelli pZero Corsa in 355/30/19 for a small price of $640 _PER_TIRE. Fok that!

A7/R7 come in 345/30ZR19. It fits.

If you want 355 then they make real slicks in that size. Cheaper than the Corsa too IIRC.

EDIT: I'm not a track pro by any means. I'm just interested in the reasoning behind the suggested setups compared with the research I have done myself.

[Snorman]

FWIW...this is very common knowledge. And it's limited to the fronts. The rears were just fine but the fronts don't last more than a day (or two). They are, however, relatively inexpensive compared to tires I've ran on other cars so I'm okay with it. $320/tire is relatively cheap for a track tire with the capabilities of the Kumho.
But yeah, I wish they were a little more durable. Suspect it is due to the very short sidewall.
S.

[ACR Steve]

"I think my fastest lap there was 1.23.xx " that would explain it . You would be faster then an Indy car at the Glen long Course..............I think your times are off :)

Go with the R7 or A7 at the track . They will survive well

[ek1]

"I think my fastest lap there was 1.23.xx " that would explain it . You would be faster then an Indy car at the Glen long Course..............I think your times are off :)

Go with the R7 or A7 at the track . They will survive well

Finally, someone is paying attention! ;)

I looked at the video again and the time is correct, except in that session we were running the Nascar configuration:
25302

The full course time was 2:04:810
25303

[stradman]

FWIW...this is very common knowledge. And it's limited to the fronts. The rears were just fine but the fronts don't last more than a day (or two). They are, however, relatively inexpensive compared to tires I've ran on other cars so I'm okay with it. $320/tire is relatively cheap for a track tire with the capabilities of the Kumho.
But yeah, I wish they were a little more durable. Suspect it is due to the very short sidewall.
S.

^^^ This. I have 2 sets of wheels and tires. And lots of front spare tires. I am expecting to get 1- 1/2 days max per front set of tires if I am caning the car. It is what it is. I don't understand why it seems you are so angry about this. Sure it would be great if you could get 5-6 days out of our tires, however when you are tracking a high downforce, heavy, front engined car and going really fast and generating a lot of G's something has to go. And in this case its the fronts. Its a simple as that. Its physics. I'm very sorry to say this and I'm sure you won't be happy in my saying this, but if you want to play with an ACR then you have to pay. Please don't take it personally either. Alternatively if you want to go with slicks then trailer the car, although that comes with other issues and ....costs

[stradman]

Oh and btw read up about tire wear over at rennlist and the 991 GT3RS .
Scroll down this thread to see some real tire wear. Says he cords them after 6-18 sessions and at some tracks after 4-5 sessions. Its not unique to the ACR I'm afraid.
https://rennlist.com/forums/991-gt3-gt3rs-and-911r/980051-understanding-tire-wear-after-track-day-2.html
I have heard similar wear with Mclaren 675Lt's as well...

[ACR Steve]

Strad- its not that hes angry . I think everyone is a little frustrated that the fronts cant hold up for 4x20 min sessions (1day)

I myself can get maybe 30 -40 min out of the fronts and that it. I race cars on veryyyy soft slicks and I can tell you this tire wear is totally unacceptable if you are tracking the car. No one would have any issue if somebody else made a race tire or slick that was our size that would wear like a normal race tire or slick. We would all buy a second set for the track and be done with it.

[ACR Steve]

Strad I am on Rennlist (Steve113) 6-18 is great wear even 4 sessions I would take (still excessive) but not being able to do a typical 4 session day with no other exact size option is way excessive wear

[stradman]

Strad- its not that hes angry . I think everyone is a little frustrated that the fronts cant hold up for 4x20 min sessions (1day)

I myself can get maybe 30 -40 min out of the fronts and that it. I race cars on veryyyy soft slicks and I can tell you this tire wear is totally unacceptable if you are tracking the car. No one would have any issue if somebody else made a race tire or slick that was our size that would wear like a normal race tire or slick. We would all buy a second set for the track and be done with it.
Sure Steve, I can understand the frustration and I accept your experience on the matter. But the fact is it is what it is, and it is certainly not unique amongst cars of this sort of capability. The problem is if you go for slicks as stand alones then you have to trailer the car and I know EK has stated in the past that this was something he wanted to avoid. Trailering has other issues as I've said. Of course it would be ideal to have slicks as only as a second set for the track-but again you would then need to have another person to take the tires/wheels to the track if you don't have arrangements to have those there.First world problems!

[ek1]

What's the point in 18" all around since A7/R7 come in stock G5 sizes already? Seems unnecessary. I was planning to just get another set of wheels in stock sizes and put some Hoosiers on them for when I want do AutoX or Track days.

Also, the Demon tires (NT05r) doesn't come in 18" for the viper but does come in stock wheel sizes. If someone were interested in drag radials.

From what I recall, going to 18"s all around opens a whole lot of tire options, including being able to buy used track tires for pennies on a dollar. By used I dont mean used like my front tires, but used as in a tire that was used in an actual race for a short period of time and has like 80% of thread left intact.

[ek1]

^^^ This. I have 2 sets of wheels and tires. And lots of front spare tires. I am expecting to get 1- 1/2 days max per front set of tires if I am caning the car. It is what it is. I don't understand why it seems you are so angry about this. Sure it would be great if you could get 5-6 days out of our tires, however when you are tracking a high downforce, heavy, front engined car and going really fast and generating a lot of G's something has to go. And in this case its the fronts. Its a simple as that. Its physics. I'm very sorry to say this and I'm sure you won't be happy in my saying this, but if you want to play with an ACR then you have to pay. Please don't take it personally either. Alternatively if you want to go with slicks then trailer the car, although that comes with other issues and ....costs

stradman - just when I thought I could come here and bitch about my tires to other Viper owners, you come along and give me a cold shoulder. What's up with that, man?

On a serious note, it's not just about having to spend money on tires. Its all the other shite that comes with it. The point of me buying an ACR rather than a real race car was not to have to deal with a trailer and all the crap that comes with that. The plan was to get a car that can be driven to the track, on the track and from the track. With the way things are now, I can't even do a 2-day track weekend on one set of fronts. And I am not even driving balls out. Last time I did that at NJMP, my fronts were toast after 4 sessions. At the same time I can't exactly bring a spare set of wheels with me in a Viper. Also, if a tire that was corded on a track happens to blow up during a drive from the track, I will be hundreds of miles away from home, in the middle of nowhere, with a 3-wheeled car that cannot even be towed without a special tow truck. Even if I make it home, I have to buy a new set of tires, take the fronts off, throw them in my SUV together with new tires, go to the tire shop, mount new tires, balance them, etc (around $60 for a pair), put the wheels back in my SUV, get home, put the wheels back on the Viper, etc. It's a pain in the ass! And it's not even that hot yet. I can only imagine what happens in summer months when ambient temps hit 90's. I may not be able to finish a day on a single set.

[ViperTony]

Go with the R7 or A7 at the track . They will survive well

Steve which size and which rims are you using for R7 or A7? Thanks.

[Special Ed]

I just ran my TA atVIR yesterday with Hoosier R7's,315 30 18 on the front and 345 30 19 on the rear. I ran five 25 minute sessions and one thirty minute session. This was the first time I ran anything other than the corsas. The only appreciable wear was on the outside edge of the front tires. I feel that I can get at least three more days of similar sessions with the fronts and probably triple that with the rears. In comparison I got 8 sessions out of the corsa's.

[ek1]

Oh and btw read up about tire wear over at rennlist and the 991 GT3RS .
Scroll down this thread to see some real tire wear. Says he cords them after 6-18 sessions and at some tracks after 4-5 sessions. Its not unique to the ACR I'm afraid.
https://rennlist.com/forums/991-gt3-gt3rs-and-911r/980051-understanding-tire-wear-after-track-day-2.html
I have heard similar wear with Mclaren 675Lt's as well...

I read that thread. 6 to 18 sessions is a huge range. I would be super happy with 18 sessions. Yet, during the last weekend at Watkins Glen (which has been repaved just last year and is in perfect condition), I managed to get about 6 sessions before one of the tires wore to the cords. I spoke to some people running PSC 2's on their cars and they get WAY more track time out of their tires - 4-6 full days on the average. Keep in mind, I an watching tire pressures and making sure I am not overheating the tires. I even moved the wing in Position 1 (less downforce) to decrease front tire scrubbing, but it did not make a lot of difference.

[ek1]

If anyone is interested, here is a long and sad list of threads dealing with ACR front tire wear in one way or another:

https://driveviper.com/forums/threads/12797-Gen-V-ACR-and-alternate-track-tires
https://driveviper.com/forums/threads/14152-Excessive-tire-wear-on-the-track
https://driveviper.com/forums/threads/14480-What-are-the-18-quot-19-quot-Wheel-choices-for-an-ACR-E-with-CCB-s
https://driveviper.com/forums/threads/14618-Brand-new-Kumho-delamination-on-2016-ACR
https://driveviper.com/forums/threads/14693-Front-Suspension-Geometry-and-Tire-Wear
https://driveviper.com/forums/threads/16037-ACR-New-Tires
https://driveviper.com/forums/threads/16672-Track-Report-ACR-on-Kumhos-Inde
https://driveviper.com/forums/threads/14176-Setup-notes-ACR-E
https://driveviper.com/forums/threads/15912-ACR-E-Watkins-Glen-weekend-impressions-info

[PkB2014]

I just ran my TA atVIR yesterday with Hoosier R7's,315 30 18 on the front and 345 30 19 on the rear. I ran five 25 minute sessions and one thirty minute session. This was the first time I ran anything other than the corsas. The only appreciable wear was on the outside edge of the front tires. I feel that I can get at least three more days of similar sessions with the fronts and probably triple that with the rears. In comparison I got 8 sessions out of the corsa's.

Good to hear. This is my plan once I shred these original Corsa.

[stradman]

Listen EK, sure I understand your frustration and desire to have front tires that last longer. Of course we would all like that. However as I said it is what it is in this car, with the given circumstances regarding existing tire makes and sizes. In the same way one can't really bitch about gas consumption on the car which is also impressive. So one needs to somehow get around this I guess. Sure slicks are one way but then you have trailered car. I think for this car if one needs to use it as a track car, then you do need to have another set of wheels and tires at the track, which is probably good practice anyway with any car, with regular track sessions. I mean you could get a puncture at the track right? What would you do then?

[VENOM V]

Guys,

I ran Hoosiers for three years on my Gen V GTS, fantasic. However one member had the belts blow out of the sidewall of an R7 on the front of an ACR twice. Two different sets, that gives me caution.

I run the Kumhos now, and am happier than many here it seems, although I wish they lasted longer in the front. I will eventually invest in the following, per input from Luke M. He had more longevity with these Pirellis than he did with Michelin slicks, although they are another option.

Pirelli DH slicks
305/645-18 front
325/705-19 rear.

They last about 6 days front, 8 days rear. Plus, they should do better on hot days above about 90 or 95 F, where the Kumhos get greasy. They raise the car about 0.3 inch, so you should lower it accordingly. Lap times are a little better than with Kumhos.

I've talked to a number of folks with 18 inch fronts, no issues on ACRs that I've heard of. Just inspect them often to be sure.

[stradman]

Guys,

I ran Hoosiers for three years on my Gen V GTS, fantasic. However one member had the belts blow out of the sidewall of an R7 on the front of an ACR twice. Two different sets, that gives me caution.

I run the Kumhos now, and am happier than many here it seems, although I wish they lasted longer in the front. I will eventually invest in the following, per input from Luke M. He had more longevity with these Pirellis than he did with Michelin slicks, although they are another option.

Pirelli DH slicks
305/645-18 front
325/705-19 rear.

They last about 6 days front, 8 days rear. Plus, they should do better on hot days above about 90 or 95 F, where the Kumhos get greasy. They raise the car about 0.3 inch, so you should lower it accordingly. Lap times are a little better than with Kumhos.

I've talked to a number of folks with 18 inch fronts, no issues on ACRs that I've heard of. Just inspect them often to be sure.

That's good to know Venom. Always good to have options. The problem is however that with aforementioned slicks, it sounds as though you won't be able to drive to the track still and then put on the slicks because as you say you will then need to lower the suspension again in which case you should corner weight/adjust again so another variable to consider. For me at least I will just drive to the track and have my mechanic bring along a couple of sets of Kumhos as spares and track like that. I know it's a luxury and an expense to have a mechanic at the trackside however for me it takes all hassle out of tracking so I can concentrate on the driving enjoyment. Unfortunately I never said it was going to be cheap... But hey ho you only live once so you might as well take the aggro out of any fun events I figure.

[VENOM V]

You could adjust the height to be a compromise between the two tires heights. About 1/8 inch lower than spec for Kumhos, it'd work for both sets. Alignment and corner weight will not change if you carefully adjust each coilover the same number of turns.

One advantage of this size slick is that the rake won't change when swapping them on.


That's good to know Venom. Always good to have options. The problem is however that with aforementioned slicks, it sounds as though you won't be able to drive to the track still and then put on the slicks because as you say you will then need to lower the suspension again in which case you should corner weight/adjust again so another variable to consider. For me at least I will just drive to the track and have my mechanic bring along a couple of sets of Kumhos as spares and track like that. I know it's a luxury and an expense to have a mechanic at the trackside however for me it takes all hassle out of tracking so I can concentrate on the driving enjoyment. Unfortunately I never said it was going to be cheap... But hey ho you only live once so you might as well take the aggro out of any fun events I figure.

[Dman]

In terms of the 18" question of why, it's just a more flexible sizing for options overall, and if you're doing a track wheel/tire setup, might as well have flexibility. The clearance potential issues are a real concern though.

As for having 2 sets and dealing with ride height and adjustment changes, I'd personally do my track wheel/tire setup and set the whole car up off of that. When not at the track and running my street wheel/tires, I wouldn't care about ride height, etc., I'd set it higher anyway for clearance. I'm not pushing the car 100mph through a double apex or set of esses on the street for consistency, I'm just tooling around like the tool that I am, lol. I'd set everything for the track and mark everything, at the track or night before, put everything to the track settings. Maybe because I'm also racing in another car I don't get overly tweaky about the Viper, I'm only doing some trackday events and not racing it, so having it set perfectly as I would if I were going for points in MARRS or something isn't a concern for me. I drive 8-9/10ths at trackdays with cushion for error so I'm not overly intense about it, but I will want tires to last a weekend, it's not about the money as much (it's not like dropping $2k in a race weekend), it's the peace of mind of not needing tires or stopping early from cording. But I'll see how it goes, all good discussion, all the good info here is really appreciated. Thx for the links ek, I've linked and marked those too for future reference now.

I'm also waiting on a report on the new R888's, it'll be interesting to see if those are exceptional. I'm lol'ing as I'm slothing my way thru breakin miles and talking about tires, am I anxious to get out there or what, woohoo.

[stradman]

All good points. So with the 18/19 inch combo front /rear what wheels are you guys using?

[Dman]

All good points. So with the 18/19 inch combo front /rear what wheels are you guys using?

I don't know about 18/19, but this is a thread with an 18/18, but I imagine you could get whatever stagger since these are Finspeed.

https://driveviper.com/forums/threads/15002-18-quot-solution-for-all-you-ACR-guys!?highlight=wheels

[Nambo]

All good points. So with the 18/19 inch combo front /rear what wheels are you guys using?

Forgeline GTD1's

[DADS ACR]

When we attended Daytona four weeks ago there were four Gen V guys there with varying set ups. All of us had the same Kumho stock tires and all of us lost front tires all weekend. We ended up leaving early because we ran out of front tires between the four of us. All of us lost chunks of tires from the inside wall. Between just three of us we used up eight tires I believe. I used up four by myself. Had a great time but wow did we destroy front tires.

25324
25325
25326
25327

I'm not sure if it was specifically a tire problem or if it was Daytona because that track is very hard on tires.
I am seriously thinking about going to an 18" x 11" front with the Nitto 315-30ZR18 NT01 thats 25.35" tall or the Toyo R888R 315-30ZR18 thats 25.5" tall. Both are close to the stock 25" height.

[ACR Steve]

That's a very scary pic and could have been disastrous. The banking on Daytona will almost double the normal tire load. With our down force those load numbers become scary for any tire. banking requires an increase in air pressure to help the tire deal with tremendous loads.

[VENOM V]

Holy crap, that is scary looking. I've never had the Kumhos chunk, but I tracked with Darius and he chunked multiple tires on different days, different tracks. The difference is that he went too hard too quickly before warming up the tires. I do one medium-pace lap, gradually building heat into the tires. I go hard on the second or third lap, never had chunking.

I am thinking that I will invest in the Forgeline GTD1s and Pirelli slicks sooner rather than later. Hot summer is coming, maybe now is a good time.

[Nemesis]

The Kumhos were developed for a specific reason, to give us the fastest lap car out there. The compromise to that is longevity, if you do not properly warm the tire up, and treat it properly, it will chunk and or blister. That is a fact of life, there are a lot of dynamics with this car and you have to understand them, push the front your going to tear/blister the tire, especially if the front isn't heated up properly, push it even harder, your going to chunk the tire. I go through a set of fronts in half a day and I do not have any chunking and or tearing, I have 20+ tires on hand at all times, and go through about two sets of fronts for every set of rears.

[RedTanRT/10]

Wow Todd, never have seen you "do 1 medium pace lap" to start a session?? Last time I was with you at BW, you and another guy took off ahead of me like you just fueled in a race and had 1 lap to go!!

My car came with 3 sets of those Pirelli's (18 rear) plus a sticker set of rains. I never ran on them but was told they were great tires. I sold the rains and then my best set to Jonathan (redsled) but haven't heard how he liked them

[ek1]

The Kumhos were developed for a specific reason, to give us the fastest lap car out there. The compromise to that is longevity, if you do not properly warm the tire up, and treat it properly, it will chunk and or blister. That is a fact of life, there are a lot of dynamics with this car and you have to understand them, push the front your going to tear/blister the tire, especially if the front isn't heated up properly, push it even harder, your going to chunk the tire. I go through a set of fronts in half a day and I do not have any chunking and or tearing, I have 20+ tires on hand at all times, and go through about two sets of fronts for every set of rears.

I always do 2 laps at slower pace to warm up the tires. I start with 24 PSI cold pressures in the front and when they get to about 28-29 PSI, I consider them to be warmed up. Do you think a couple of laps is enough? I also try to make an effort not to overdrive the front tires, meaning if I feel the car pushing, I back off a bit. Finally, I moved the wing to Pos 1 (least downforce) to get more in the front. From the past season I learned that when hot pressures reach about 35 PSI, the tire is almost guaranteed to be destroyed due to overheating, so I never get to that point. Highest pressure I saw last time was about 32 PSI and my hot tire temps were in the 160-180F range, with relatively small delta (about 20F) between outside, middle and inside. Aside from switching to another brand, I feel that there may be a "recipe" to make these tires last longer (while still driving fast), I just don't know how to learn it.

How did you go through a set in half a day? High ambient temps?

[bluesrt]

Try to trailbrake to kill the push.

[ek1]

Try to trailbrake to kill the push.

Yep, doing that already. It does not push that much because I am trying to avoid it by going into corners slower and getting on power earlier. Still killing the fronts though.

[bluesrt]

Hit the corner harder. But befor normal brake and push that pedal. Blend the car around the turn. Its a art. But simple if u keep calm

[bluesrt]

Trail brake it

[ek1]

Hit the corner harder. But befor normal brake and push that pedal. Blend the car around the turn. Its a art. But simple if u keep calm

Hitting corners harder is scary :) I'll try that at the next track day @ Pocono. Infield is almost completely flat, with lots of grass runoff - nothing to hit.

[ACR Steve]

Tony - I haven't tracked the car since I chunked tires at Monticello race track last fall. Not sure which sixe a or r 7 I will go with on front but should be easy to figure out

EK-1 - my car is very neutral on track. Actually its the easiest fast car I have ever driven on track. Check you alignments,shocks and corner balance numbers.

If you Push at the entrance of a turn work with the front of the car .Soften the front or lower front ride height

A push at exit then you work with the rear. Stiffen rear compression or raise rear ride height

Mid Corner push(understeer) tougher to analyze but you need to pre load more or stiffen the front usually sway bar but ours I don't think are adjustable. Its weird with mid corner its almost opposite . Tough to figure more of a trial by error

Always keep in mind your line. Our cars turn in supper fast .That makes many people turn in to early leading to understeer at entrance and exit. Lastly put it in your calendar Friday Aug 25 at Lime Rock NY/Ct Viper track day in conjunction with NASA it will be a great time

[38D]

Inadditontomorepressure, you typically need to runlesscamberat daytona with the banking to avoid overheating the inside. I took out a full degree (from ~3.0 to2.0) for Daytona back when I ran my 911 turbo.

[ek1]

Seems like the most logical course of action. I dont care what someone, somewhere on some online thread posts. I would go to the source and get a resolution. Some people simply like to complain but not really accomplish anything

Speaking of complaining. I called Tire Rack last week and spoke to them. They said they would get one of their Kumho purchasers call me. Good thing I didn't start holding my breath for a call back, 'cause I'd be long dead by now.

[A C R]

I also was promised a return call from Tire Rack a month ago ---- still waiting

[Arizona Vipers]

Yep, doing that already. It does not push that much because I am trying to avoid it by going into corners slower and getting on power earlier. Still killing the fronts though.

Lower your wing setting to #1. Trust me on this.

[Arizona Vipers]

I've been running 18" wheels and Hoosiers on my ACR for about a year. I got 18 sessions with R7's and about 10-12 with A7's before they cord.
It's the first mod I did. I ordered the wheels before I even found my ACR lol.

[ek1]

Lower your wing setting to #1. Trust me on this.

I do trust you on this, and my wing has been in position 1 since last year. No change to the front tire wear pattern / longevity though.

[ek1]

I've been running 18" wheels and Hoosiers on my ACR for about a year. I got 18 sessions with R7's and about 10-12 with A7's before they cord.
It's the first mod I did. I ordered the wheels before I even found my ACR lol.

Any damage to the calipers and/or rims due to rocks lodged in between?

[JonB ~ PartsRack]

Speaking of complaining. I called Tire Rack last week and spoke to them. They said they would get one of their Kumho purchasers call me. Good thing I didn't start holding my breath for a call back, 'cause I'd be long dead by now.

Since you bought them from PartsRack, I called for you. I Sent them your pix. Herewith their reply:


A picture is worth a thousand words.

This tire isn’t delaminating because of a problem with the tire. It has simply worn out in the shoulder area. Many people with many different tires used on the track get to the bottom of the tread rubber compound and think it is delaminating when it wears through or begins to peel back.


The bottom of the major grooves and lateral notches show us where the bottom of the tread rubber is. When you compare the worn versus new tire you can see the lateral notches in the outboard shoulder are worn to zero. In the outboard shoulder the tread rubber has worn to zero, essentially. The patches in the shoulder that have torn away show what little tread rubber remains is super-thin. When at hot track temperature under very high lateral loads the tread rubber can begin to peal ay in patches. I see the area inboard of the shoulder that is circled. There appears to be a circumferential band of wear in this area, too. Often with wide asymmetric shoulder patterns there can be an area in the tread that buckles a little during hard cornering, that creates a wave pattern in the pressure distribution as you move from the outermost edge towards the center and inboard shoulder. The high points of contact pressure create more wear than the lower pressure areas on either side.

Work = heat = wear. If we can find one of these we know where the other two are occurring. Looking at the wear pattern there is more wear on the outboard shoulder than the inboard shoulder. That tells me the tire wants more negative camber for track use. We have plenty of reports from track users of the Viper ACR that it has a fair amount of understeer at the limit, like most road-going cars.

Dial in more negative camber, drive corner entry so that you eliminate understeer, and maybe try a little more air pressure to try and help stabilize the footprint a little more to flatten out the pressure distribution in the outboard shoulder.

aoladp://MA30679390-0007/image001.png

[Arizona Vipers]

Any damage to the calipers and/or rims due to rocks lodged in between?

Yes, a little. Mostly to the wheel barrel. Just on the fronts. This only happens on the dirty tracks i ran (Wild Horse Pass tracks). Cleaner tracks like INDE, Chuckwalla, Spring Mountain no rocks get in the barrels at all unless you go off track.
Worst case scenario if you run a lot on dirty tracks, you'll be replacing your front wheels every 1-2 years to be on the safe side.

[ek1]

Guys,

Great news! I just did a 5-session track day at Lime Rock with Hoosier R7 295/30/19 on the front (stock Kumhos on the rear still). I was driving at 7/10th the first 4 sessions and 8/10th the 5th session. Also most of one 3rd session was driven by Steve at my 12/10ths of my pace. Sessions were about 20-25 min each. The Hoosiers still look great (I will post pictures later), no delamination, no uneven wear, etc. And I drove on them to and from the track as well. Tire pressures remained stable (did not shoot up 10psi in one session like Kumhos) and temperatures were good as well. I have not seen any rubbing either. I'll post pics of tires later as well.

For pressures, I started with 26.6 cold on both fronts and I believe I ended up with like 32-33 hot. Only had to bleed once in the entire day and even that was not absolutely required.

Ride height it set up at the SRT recommended track height in the ACR supplement. Shocks are set up as per SRT recommended track height in the ACR supplement. I will post camber and toe in settings later once Chuck confirms them.

The only slight negative I noticed (compared to Kumhos) was a slight decrease in front grip (not more than 5%-10%).

So there you have it, folks....great solution to front Kumho tire problem.

[stradman]

L

Guys,

Great news! I just did a 5-session track day at Lime Rock with Hoosier R7 295/30/19 on the front (stock Kumhos on the rear still). I was driving at 7/10th the first 4 sessions and 8/10th the 5th session. Also most of one 3rd session was driven by Steve at my 12/10ths of my pace. Sessions were about 20-25 min each. The Hoosiers still look great (I will post pictures later), no delamination, no uneven wear, etc. And I drove on them to and from the track as well. Tire pressures remained stable (did not shoot up 10psi in one session like Kumhos) and temperatures were good as well. I have not seen any rubbing either. I'll post pics of tires later as well.

For pressures, I started with 26.6 cold on both fronts and I believe I ended up with like 32-33 hot. Only had to bleed once in the entire day and even that was not absolutely required.

Ride height it set up at the SRT recommended track height in the ACR supplement. Shocks are set up as per SRT recommended track height in the ACR supplement. I will post camber and toe in settings later once Chuck confirms them.

The only slight negative I noticed (compared to Kumhos) was a slight decrease in front grip (not more than 5%-10%).

So there you have it, folks....great solution to front Kumho tire problem.

Hi Eugene.. Can I ask, I presume you had to redo your geo once you got the hoosiers on the fronts right?

[stradman]

Also instead of running slicks at that size why not just fit michelin cup sport 2 's which are OK and useful in case it rains and from my experience on other cars seem to last well?

[Racingswh]

Nice!

How was it riding with Steve? :)

Were you surprised at how quick the car is in the downhill? Did it come off the ground in the uphill if not running the chicane?

He has a ton of experience at that track.

[ViperGeorge]

Guys,

Great news! I just did a 5-session track day at Lime Rock with Hoosier R7 295/30/19 on the front (stock Kumhos on the rear still). I was driving at 7/10th the first 4 sessions and 8/10th the 5th session. Also most of one 3rd session was driven by Steve at my 12/10ths of my pace. Sessions were about 20-25 min each. The Hoosiers still look great (I will post pictures later), no delamination, no uneven wear, etc. And I drove on them to and from the track as well. Tire pressures remained stable (did not shoot up 10psi in one session like Kumhos) and temperatures were good as well. I have not seen any rubbing either. I'll post pics of tires later as well.

For pressures, I started with 26.6 cold on both fronts and I believe I ended up with like 32-33 hot. Only had to bleed once in the entire day and even that was not absolutely required.

Ride height it set up at the SRT recommended track height in the ACR supplement. Shocks are set up as per SRT recommended track height in the ACR supplement. I will post camber and toe in settings later once Chuck confirms them.

The only slight negative I noticed (compared to Kumhos) was a slight decrease in front grip (not more than 5%-10%).

So there you have it, folks....great solution to front Kumho tire problem.

What did you do with the ride height? I think the front Hoosiers you ran would have been an inch or more taller than the Kumhos. If you didn't adjust height in the rear you would have reduced the rake.

[bluesrt]

think they say lower in front 3 turns/ raise rear 1 turn when running hoosier in those sizes stated here?????

[docwviper]

I was told by some guys who race in the trans am series the Pirelli is more prone to puncture? Did you ever get these put on? The R7 sidewall blowout is scary. Has this happened with the Pirelli.


Guys,

I ran Hoosiers for three years on my Gen V GTS, fantasic. However one member had the belts blow out of the sidewall of an R7 on the front of an ACR twice. Two different sets, that gives me caution.

I run the Kumhos now, and am happier than many here it seems, although I wish they lasted longer in the front. I will eventually invest in the following, per input from Luke M. He had more longevity with these Pirellis than he did with Michelin slicks, although they are another option.

Pirelli DH slicks
305/645-18 front
325/705-19 rear.

They last about 6 days front, 8 days rear. Plus, they should do better on hot days above about 90 or 95 F, where the Kumhos get greasy. They raise the car about 0.3 inch, so you should lower it accordingly. Lap times are a little better than with Kumhos.

I've talked to a number of folks with 18 inch fronts, no issues on ACRs that I've heard of. Just inspect them often to be sure.

[ek1]

L


Hi Eugene.. Can I ask, I presume you had to redo your geo once you got the hoosiers on the fronts right?

Yes, I did.

My current suspension geometry is as follows:

Front: -2.4 Camber, Toe in 0
Rear: -1.0 Camber, Toe in 0.2

As per Chuck, these are the same settings Bondurant uses in their Viper school.

I am considering going to 0 toe in the rear based on Steve's feedback about the rear end having a wiggle under hard braking.

[Hemibob]

How would handling be effected by a less aggressive alignment for the street? I killed my fronts in 5k miles of street driving. Lots of canyon driving, but just the insides of both fronts showing cord. Rest of the tire fine.

[Arizona Vipers]

think they say lower in front 3 turns/ raise rear 1 turn when running hoosier in those sizes stated here?????

Why is anyone guessing with "clicks and turns"? Ride height for the track needs to be set at 4" front and 5.5" rear. I don't know how many articles I've read with the factory engineers and Tom O'dell etc all stating the manual recommended rake/frame height is extremely important. We are fortunate to have car that has been flogged on a track to break many track records and given this data by the engineers.

[stradman]

Why is anyone guessing with "clicks and turns"? Ride height for the track needs to be set at 4" front and 5.5" rear. I don't know how many articles I've read with the factory engineers and Tom O'dell etc all stating the manual recommended rake/frame height is extremely important. We are fortunate to have car that has been flogged on a track to break many track records and given this data by the engineers.
True words

[ek1]

Nice!

How was it riding with Steve? :)

Were you surprised at how quick the car is in the downhill? Did it come off the ground in the uphill if not running the chicane?

He has a ton of experience at that track.

Riding with Steve was awesome. He is the man! He could not really push it since the session that he drove in was still group C (point by's required) and there were too many cars in the group, so the car did not come off the ground (we were not running the chicane). He did show me pictures of him driving the Cup car there. Or rather flying the Cup car because it was like a foot off the ground :) Insane!

I got a looooong way to go and a lot more to learn. Hopefully I'll get some rides with him at Lime Rock in August.

[ek1]

How would handling be effected by a less aggressive alignment for the street? I killed my fronts in 5k miles of street driving. Lots of canyon driving, but just the insides of both fronts showing cord. Rest of the tire fine.

As you may remember, some people here consume a set of fronts in 3-4 track sessions 20 minutes each. If you are doing "a lot" of canyon driving, especially in high temps and at high speeds, I am surprised your fronts lasted 5K miles.

What are your current camber/toe in settings? Also post pics of your tires.

[ek1]

What did you do with the ride height? I think the front Hoosiers you ran would have been an inch or more taller than the Kumhos. If you didn't adjust height in the rear you would have reduced the rake.

The ride height was adjusted to be 4" in the front and 5.5" in the rear (SRT recommended settings) after R7s were mounted. I actually got more rake than before since the car was previously set to 4.5" with Kumhos (I had to drive it from Woodhouse to home 1,500 miles on public roads).

[ek1]

Also instead of running slicks at that size why not just fit michelin cup sport 2 's which are OK and useful in case it rains and from my experience on other cars seem to last well?

R7s are not really slicks. Having said that, I didn't actually realize that PSC2's are available in 295/30/19, but I just checked Tire Rack and they apparently are now. Not only that, there are more tires in that size (PSS, PSS P2, Yokohama, etc.) Some of those are super cheap (Toyo Proxes R888R for $295/ea.). The crazy part is - there is even an all-season 295/30/19 Bridgestone tire available now for people who want to drive their ACRs in colder temps.

Because I mostly drive to/from the track, I'll see how long R7s last. Besides, other tires will have different diameters (295/30/19 PSC2 is 26" while 295/30/19 R7 is 26.1") so I will need to get the car realigned and height adjusted again (mucho dinero).

In other piece of good news, there are now more tires available in the rear P355/30ZR19 size: Pirelli Pzero and Pzero Corsa. The regular PZero is actually cheaper than the Kumho, but obviously won't have as much grip.

[Racingswh]

Riding with Steve was awesome. He is the man! He could not really push it since the session that he drove in was still group C (point by's required) and there were too many cars in the group, so the car did not come off the ground (we were not running the chicane). He did show me pictures of him driving the Cup car there. Or rather flying the Cup car because it was like a foot off the ground :) Insane!

I got a looooong way to go and a lot more to learn. Hopefully I'll get some rides with him at Lime Rock in August.

The traffic is the biggest challenge at Track Day events. These cars really need to be in TT events so there won't be so many other cars in the way. The closing rates and speed disparity almost makes you laugh out loud sometimes.

Camera's are ready BTW for next weekend. Decided to go inside the car with a very short articulating ball ram mount just so there is better audio. I bought 2 setups, one for my Wife's car and one for the Viper. Can't wait to see how they do.

Car is set up with the 315/30/18 A7's front and 345/35/18 A7's rear, rake at 4.05" F and 5.5"R. Adjustable end links added and the car is properly corner weighted for the first time. I don't run balanced wheels typically but this time they did it out of habit. If anyone goes with 18's balancing weights have to be mounted carefully as they will drag on brake ducts or hit the calipers. Something to be aware of when going with the smaller diameter wheels.

That pic of Steve that high off the ground is awesome. I have seen big wheelies there but never a pure jump through the air like that shot of Steve flying his car over the uphill. My friend Bob Smith was there at Limerock that day testing his own Cup car as well and posted up the pic even before I think Steve had seen it. lol!!

Glad you got the front tire deal sorted to your liking. On the A7's I get 18 sessions out of the fronts and over 30 out of the rears. We mark the tires for every session each one has done so we have a great handle on tire life and wear. They are also faster for longer than the Kumho's in a given session. I imagine your R7's will last even longer.

When is your next event? We are at NJMP next weekend and Watkins Glen end of July. Looking for more events to fill August and some in the fall.

[stradman]

So can I correctly assume that by putting 295/30/19 on the car, and because of the 3cm wider overall diameter of the tire /wheel the edge of the front splitter will be sitting 1.5 cm higher than it would be with the 295/25 Kumhos? If so does anybody know if this is relevant to the aero?

[Hemibob]

As you may remember, some people here consume a set of fronts in 3-4 track sessions 20 minutes each. If you are doing "a lot" of canyon driving, especially in high temps and at high speeds, I am surprised your fronts lasted 5K miles.

What are your current camber/toe in settings? Also post pics of your tires.

All settings are factory. 2644026441

[ACR Steve]

Thank guy :)


Racingswh- come on up to our event at Lime Rock Aug 25th its in conjunction with NASA . They have HPDE ,Time Trials and racing. We will have a ton of Vipers I will also bring the Cup car out and do the race

[stradman]

Because I mostly drive to/from the track, I'll see how long R7s last. Besides, other tires will have different diameters (295/30/19 PSC2 is 26" while 295/30/19 R7 is 26.1") so I will need to get the car realigned and height adjusted again (mucho dinero).

.

So will you be driving them on the street? I thought they're not road legal?

[bluesrt]

if I remember, I put a little more camber in the car, like about almost 3 degrees, set toe at 0 and it stopped doing/cording the left front outer tire/ the pretty much run evan wear on both fronts now

[ACR Steve]

R7 is a DOT legal tire they are not a slick

[stradman]

R7 is a DOT legal tire they are not a slick

Yes Steve but that does not make them road legal right? As according to Tire Rack:
WARNING: DOT labeled Hoosier Racing Tires meet Department of Transportation requirements for marking and performance only and are NOT INTENDED FOR HIGHWAY USE. It is unsafe to operate any Hoosier Racing Tire, including DOT tires, on public roads. The prohibited use of Hoosier Racing Tires on public roadways may result in loss of traction, unexpected loss of vehicle control, or sudden loss of tire pressure, resulting in a vehicle crash and possible injury or death.

[ek1]

Stradman - Not sure how it is in UK, but here in US anyone can sue anyone for anything. End result is that every company that sells anything in the US has these nice disclaimers saying that using their products in some way can result in injury or death. This is why our fast food restaurants sell coffee in cups that say "CAUTION!!! The coffee is hot!!!" and also why every Navi on every car sold in the US pops up a message saying "Don't enter info while driving and by the way, we are also not responsible if our system navigates you into a lake". In my mind, this interferes with a process of natural selection and must be avoided at all costs. People that don't know that coffee can be hot should not be allowed to procreate.

In case of Hoosier, they put these disclaimers out it in case some moron decides to do a cross-country drive on a set of R7s, one blows up, he dies and his wife sues Hoosier because they provided "defective" tires. Remember how Paul Walker's wife tried to sue Porsche? How insane was that?

A few things about driving with R7s though.

First, if you do drive them on a public road, they tram line like CRAZY. It almost caught me off guard the first time it happened. The entire area where I live is basically a perpetual construction zone, with broken, damaged and rough roads, so having a good grip on the wheel and expecting the car to dart is a good strategy.

Second, the tires are very soft, which means they are a lot more likely to get punctured by road debris than regular tires. Both of my R7 fronts have a slow leak now (like 1 PSI a day) after a drive back from Lime Rock last month. I'll probably use them for a few more track days and replace them.

[ek1]

Alright.....so here is the deal with 295/30ZR19 Hoosier R7s in the front:

These tires are AWESOME on the track. They wear MUCH better than Kumhos, they do not fall off after a few hot laps like Kumhos and only have a tiny bit less turn-in grip than Kumhos. The only way to feel the difference is to drive on Kumhos vs R7s within a single week or so. There is no rubbing that I could see or feel.

Now...the shitty news. It's not that the car darts and tramlines like hell on public roads. That's not a problem. Even driving on R7s in the rain in the event of emergency is not a problem.

The problem is that after only a few drives to/from the track, BOTH front tires have a slow leak. I have not even driven through construction zones or anything and yet they have apparently been punctured. They lose about 5 PSI per day. Still usable, but maybe not for a full-on track day. I'll do an autocross with them on the 5th and see what happens, but overall I am really sad. There goes yet another attempt to have a car with tires that last more than 1 track day. FUCK!

[AZTVR]

The problem is that after only a few drives to/from the track, BOTH front tires have a slow leak. I have not even driven through construction zones or anything and yet they have apparently been punctured.

I think that it would be awesome to see an ACR towing a tire trailer to the track ! Just saying.

[ek1]

I think that it would be awesome to see an ACR towing a tire trailer to the track ! Just saying.

Don't think I haven't considered that. It's not possible due to the rear diffuser and the belly pans. I think I may end up dropping off a pair of wheels at a few local tracks I go to (Lime Rock, NJMP, Watkins Glen and Pocono) and just using them as needed.

What a pain in the ass.

[Arizona Vipers]

I think that it would be awesome to see an ACR towing a tire trailer to the track ! Just saying.

Me too!

- - - Updated - - -


Don't think I haven't considered that. It's not possible due to the rear diffuser and the belly pans. I think I may end up dropping off a pair of wheels at a few local tracks I go to (Lime Rock, NJMP, Watkins Glen and Pocono) and just using them as needed.

What a pain in the ass.

Roof rack!!!! :dude3:

[Arizona Vipers]

Alright.....so here is the deal with 295/30ZR19 Hoosier R7s in the front:

These tires are AWESOME on the track. They wear MUCH better than Kumhos, they do not fall off after a few hot laps like Kumhos and only have a tiny bit less turn-in grip than Kumhos. The only way to feel the difference is to drive on Kumhos vs R7s within a single week or so. There is no rubbing that I could see or feel.

Now...the shitty news. It's not that the car darts and tramlines like hell on public roads. That's not a problem. Even driving on R7s in the rain in the event of emergency is not a problem.

The problem is that after only a few drives to/from the track, BOTH front tires have a slow leak. I have not even driven through construction zones or anything and yet they have apparently been punctured. They lose about 5 PSI per day. Still usable, but maybe not for a full-on track day. I'll do an autocross with them on the 5th and see what happens, but overall I am really sad. There goes yet another attempt to have a car with tires that last more than 1 track day. FUCK!

Did you find out what punctured it? Could be bad valves or something. I drive my Hoosier's on the street all the time ( I never swap to street tires) and in three years I've only had one leak.

[ACR Steve]

NY roads VS Arizona totally different worlds

The problem is the R7 doesn't have the thick steel belts like a conventional tire. Its built to be light weight so it cant take the pot holes, gaps in the road, steel plates and the other everyday apocalyptic things on our roads.

[Dan Cragin]

These Kuhmo tires can give some great lap times but need to be managed carefully or they won't last. At tracks like Fontana or Willow Springs, if you don't have an asymmetrical alignment, carefully get the tries up to temperature and manage tire pressures, the fronts won't last more than 2 sessions.

Understand these tires are softer than most slicks, have tread blocks (which heat up fast) and the sidewall is very small, which concentrates the load. That combined with 3000 plus pounds of down force from the Aero Package, makes for a real tire eater.

I was told when the ACRE broke all the track records, the tires were replaced after every session!

Many folks have changed to R7's and 18 inch wheels. One note on slicks, I have not found slicks other than the DOT R7 Hoosier that are rated for the load of the ACRE. That could result in a catastrophic tire failure. Just because it fits, does not mean its right.

[Arizona Vipers]

NY roads VS Arizona totally different worlds

The problem is the R7 doesn't have the thick steel belts like a conventional tire. Its built to be light weight so it cant take the pot holes, gaps in the road, steel plates and the other everyday apocalyptic things on our roads.

Yeah your roads are indeed crazy, I took the family on a road trip last summer and drove in NYC. Wow what a culture shock. LOL I thought he is describing a slow leak, not a tear from a pot hole. Hoosiers sidewalls are much stronger than you think, they are designed to smack off track curbing at very high speeds and to not roll over on high speed turns

[ek1]

Did you find out what punctured it? Could be bad valves or something. I drive my Hoosier's on the street all the time ( I never swap to street tires) and in three years I've only had one leak.

No, I haven't taken them off yet. I don't think it's bad valves because I had these tires mounted late last year, they spent the entire winter in the garage and have not lost any air. There is another thread here :

https://driveviper.com/forums/threads/17651-Hoosier-R7-s-Who-has-track-with-them-thoughts-and-impressions/page2 where another owner says R7s are horrible from puncture resistance perspective.

I know I have not hit any potholes though. It must be something small and sharp. I considered using a bit of fix-a-flat but decided against it because I dont know how it will react to track temps. For now I am going to use the tires as is and will just add air until they heat cycle out or wear out. They only have 2 track days on them.

[ek1]

Me too!

- - - Updated - - -



Roof rack!!!! :dude3:

And don't think I have not considered that as well :). There is a company called Sea Sucker and they make insane roof racks that use powerful suction cups. Check it out: https://www.youtube.com/watch?v=6kp6qZ-Mah4

Their rack cannot sustain the weight of two front wheels though. I asked. Not safe.

[ViperGeorge]

No, I haven't taken them off yet. I don't think it's bad valves because I had these tires mounted late last year, they spent the entire winter in the garage and have not lost any air. There is another thread here :

https://driveviper.com/forums/threads/17651-Hoosier-R7-s-Who-has-track-with-them-thoughts-and-impressions/page2 where another owner says R7s are horrible from puncture resistance perspective.

I know I have not hit any potholes though. It must be something small and sharp. I considered using a bit of fix-a-flat but decided against it because I dont know how it will react to track temps. For now I am going to use the tires as is and will just add air until they heat cycle out or wear out. They only have 2 track days on them.

Look at the bead all around the wheel. Sometimes they don't fully seat and they then have a slow leak. If the bead doesn't look to be against the rim all around you can sometimes remove all the pressure, squirt some dish detergent around the bead where it isn't seated then blow up to 50psi to seat it.

[ek1]

Look at the bead all around the wheel. Sometimes they don't fully seat and they then have a slow leak. If the bead doesn't look to be against the rim all around you can sometimes remove all the pressure, squirt some dish detergent around the bead where it isn't seated then blow up to 50psi to seat it.

Unfortunately the bead looks good on both sides.

[ACR Steve]

Only way is the bathtub or pool test - take the wheel off and dunk it .

My bet is a small slice in the surface of the tire, Potholes even small sharp corner ones ,glass , metal or anything on the road will go through them like butter.



AV-As for the side walls they aren't as strong on a Hoosier as everyone thinks. Our Kumo's were designed for insane side wall load . Hoosiers have a long documented history of the sidewall blowing out on rear engine hi load cars ( Porsche GT3's and Cups) I bet our cars in the front carry more load at speed then the rears of 911's. Not saying don't use Hoosiers just don't think they are indestructible on track. Always manage your tires

[ek1]

Only way is the bathtub or pool test - take the wheel off and dunk it .

My bet is a small slice in the surface of the tire, Potholes even small sharp corner ones ,glass , metal or anything on the road will go through them like butter.



AV-As for the side walls they aren't as strong on a Hoosier as everyone thinks. Our Kumo's were designed for insane side wall load . Hoosiers have a long documented history of the sidewall blowing out on rear engine hi load cars ( Porsche GT3's and Cups) I bet our cars in the front carry more load at speed then the rears of 911's. Not saying don't use Hoosiers just don't think they are indestructible on track. Always manage your tires

Steve - thank you! I can't believe I didn't think about the bathtub!!! DUH!!!!

I'll do that on Sunday after I come back from the Autocross event.

[Dman]

Steve - thank you! I can't believe I didn't think about the bathtub!!! DUH!!!!

I'll do that on Sunday after I come back from the Autocross event.

It's easier to just take a simple plastic spray bottle, put some soft soap in and fill with water, spin the wheel slowly on the car and spray all over the tread area, the leak will blow tiny bubbles. I found a tiny microscopic puncture on my rear ACR tire that otherwise you'd never have thought was a leak, it was dropping maybe 2psi a week, real sneaky leak but no match for soap. It's a tried and true method and hella easier than lugging the tire off and dragging it to a bath tub, especially past your wife, lol.

[ek1]

It's easier to just take a simple plastic spray bottle, put some soft soap in and fill with water, spin the wheel slowly on the car and spray all over the tread area, the leak will blow tiny bubbles. I found a tiny microscopic puncture on my rear ACR tire that otherwise you'd never have thought was a leak, it was dropping maybe 2psi a week, real sneaky leak but no match for soap. It's a tried and true method and hella easier than lugging the tire off and dragging it to a bath tub, especially past your wife, lol.

How did you fix the leak? I am afraid to let the tire shop use a plug because it may come out when tires heat up to track temps.

[Chorps]

It's easier to just take a simple plastic spray bottle, put some soft soap in and fill with water, spin the wheel slowly on the car and spray all over the tread area, the leak will blow tiny bubbles. I found a tiny microscopic puncture on my rear ACR tire that otherwise you'd never have thought was a leak, it was dropping maybe 2psi a week, real sneaky leak but no match for soap. It's a tried and true method and hella easier than lugging the tire off and dragging it to a bath tub, especially past your wife, lol.

Taking a bubble bath with your tire will surely result in a raised eyebrow from the wife.

[ek1]

Another VERY interesting update on the front Hoosiers.

THERE ARE NO PUNCTURES and NO DAMAGE to the either one of the R7s. No damage to the rims either. I pulled both front wheels off yesterday and discovered that the leak is around the bead.:

2773127732

I'll take the wheels to the tire shop next week and have them remount the tires. But now I need to understand why this started happening in the first place. The tires were mounted at Woodhouse late last year and sat in my house the entire winter with zero leaks. After 3 track days they started leaking.

Maybe someone with a lot of track experience can chime in? I put a wheel off here and there and had 2 wheels off once, but no excursions into gravel traps, sand, or anything that would break the seal.

[38D]

You can break the bead if you go too fast before pressure has built.

[ViperTony]

You can break the bead if you go too fast before pressure has built.

This.


Another VERY interesting update on the front Hoosiers.

Eugene, you ran these at the AutoX right? No leaks until now? What cold tire pressure do you start at?

[dewilmoth]

Has anyone confirmed that running an inch taller front tire is in fact a problem on the ACR? Obviously the rake would need to be re-adjusted, but it would really open up tire options. It seems like everyone has just assumed it won't work but I can't find any real info. I'm interested in the Trofeo R.

[ACR Steve]

It works fine just raise ride height for proper rake.

[ACRucrazy]

I'm interested in the Trofeo R.

You're not the only one.

[Dan Cragin]

Most likely you got gravel in the bead when you put a tire in the dirt.

[ek1]

This.



Eugene, you ran these at the AutoX right? No leaks until now? What cold tire pressure do you start at?

Yeah I ran these at Auto X. The leaks started waaay before that. I came packing a portable compressor and adjusted tire pressures before each session :). From what I recall my cold pressures were 32 all around and then I believe Steve recommended to drop 1 PSI on both left wheels. I am not 100% sure though.

[ek1]

Has anyone confirmed that running an inch taller front tire is in fact a problem on the ACR? Obviously the rake would need to be re-adjusted, but it would really open up tire options. It seems like everyone has just assumed it won't work but I can't find any real info. I'm interested in the Trofeo R.

Wait....who said it's a problem? It works perfectly fine, at least for me and several others on here provided the car is aligned and height-adjusted properly to compensate for taller tires.

Trofeo R is freaking $521 per tire though. If they deliver the same grip as Hoosier R7s and last a bit longer, I can see myself investing into a set. But otherwise, no way!

[ek1]

Most likely you got gravel in the bead when you put a tire in the dirt.

That's what I'm hoping for. Will take tires to the shop this weekend. Fingers crossed.

[Arizona Vipers]

Has anyone confirmed that running an inch taller front tire is in fact a problem on the ACR? Obviously the rake would need to be re-adjusted, but it would really open up tire options. It seems like everyone has just assumed it won't work but I can't find any real info. I'm interested in the Trofeo R.
You'll be fine at 1". On my ACR I run a 335-30-18 front 1" taller than stock and a 345-35-18 rear that is over 1" shorter than stock (stock is 24.8") with zero and I beat this car to an inch of it's life on the track.
Remember a 1" taller tire is really only half inch on each side. Tires vary more than half an inch just with tire pressures. Lower your pressures to 20 psi, then pump them up to 40 and watch how much your car raises up.
If a 1" change in tire size cause stability control problems, it would be happening to everyone on stock tires as pressures varied.

[stradman]

Wait....who said it's a problem? It works perfectly fine, at least for me and several others on here provided the car is aligned and height-adjusted properly to compensate for taller tires.

Trofeo R is freaking $521 per tire though. If they deliver the same grip as Hoosier R7s and last a bit longer, I can see myself investing into a set. But otherwise, no way!
Trofeo R's will likely disintengrate as quickly as Kumhos's on the ACR-and cost more. Ask the 675 LT Mclaren guys about their experience and they will confirm.......

[Stubbygda]

Another VERY interesting update on the front Hoosiers.

THERE ARE NO PUNCTURES and NO DAMAGE to the either one of the R7s. No damage to the rims either. I pulled both front wheels off yesterday and discovered that the leak is around the bead.:

2773127732

I'll take the wheels to the tire shop next week and have them remount the tires. But now I need to understand why this started happening in the first place. The tires were mounted at Woodhouse late last year and sat in my house the entire winter with zero leaks. After 3 track days they started leaking.

Maybe someone with a lot of track experience can chime in? I put a wheel off here and there and had 2 wheels off once, but no excursions into gravel traps, sand, or anything that would break the seal.


i had same issue on my ta2. hoosier told me to scotchbrite the beads and to use hairspray when mounting tires. also must be dry mounted. worked for me.

[BlueAdder]

28365

After 6 heat cycles.
I was trying the same Kumho but this time I ordered them shaved because I wanted to know if it would make a difference.
Turns out that they lasted even less than the non shaved one. So, either I got faster, which is highly unlikely or the fact that there was less rubber ended up making their life shorter.

I'll just buy regular V720 from now on.
I'm also looking at going to 18" front but that really tiny clearance (CCB) between the calipers and the wheel is really worrisome.

[stradman]

28365

After 6 heat cycles.
I was trying the same Kumho but this time I ordered them shaved because I wanted to know if it would make a difference.
Turns out that they lasted even less than the non shaved one. So, either I got faster, which is highly unlikely or the fact that there was less rubber ended up making their life shorter.

I'll just buy regular V720 from now on.
I'm also looking at going to 18" front but that really tiny clearance (CCB) between the calipers and the wheel is really worrisome.

So does that equate to 1 track day for you? It would for me if each cycle about 20 minutes. I usually do maybe 1 20 minute cycle per hour at most. What track were you running? Is the track smooth or roughish? Track temps? So many different variables to take into consideration for tire wear. I usually get about 8-9 heat cycles and of course it helps to swap sides on the front mid way. Last time I got about 12 cycles out of them but maybe that was the circuit

[BlueAdder]

You're correct, that's about 1 full track day. usually we get 5 to 6 sessions of 20min each.
I had 5 sessions at Sonoma Raceway on the 08/21, and the track is relatively smooth. Temperatures were in the 80F-90F range, so nothing too horrendous.
On Monday I was at Thunderhill (Willows, CA) the track is rougher and the temperature outside was 90F-100F and even though it was overcast in the morning, it was still pretty hot especially when I had my first and only real session.

I don't swap sides because the tires usually look just as bad on the other side and swapping them buys me nothing. There is just too much camber and I'm running the SRT specs (-2.8 front).
That being said, the tires were shaved so there was less material and therefore I think that it's probably why they ended this way so quickly. Like you, they usually last me a couple of track days (10 heat cycles) but we're the lucky ones. I know some guys who will get at most 5 sessions out of the set of front tyres (wrote it this way to make you happy :p)

[Bruce H.]

I wonder if the higher ambiant temps on the day you used the shaved tires negated the anticipated advantage of cooler tire temps from less tread squirm?

It may be that the fast cooking of the minimal volume of air inside these ultra low profile front tires has a greater impact on tire temps and damage from overheating than tread depth can compensate for, and that increased ambiant and internal air temps have a disproportionate impact on breaking down the tire.

[Smokin]

I was told that traction control is defeated when a taller tire is selected. Has anyone validated/refuted this?

[docwviper]

I was told that traction control is defeated when a taller tire is selected. Has anyone validated/refuted this?

That is interesting.... Anybody?

[BlueAdder]

I was told that traction control is defeated when a taller tire is selected. Has anyone validated/refuted this?

That shouldn't be a worry since ESC should be either in track mode or full off at the track. If you leave it on, you end up cooking your rear brakes...

[ViperGeorge]

I was told that traction control is defeated when a taller tire is selected. Has anyone validated/refuted this?

I got this directly from Erich Heuschele, SRT's Vehicle Dynamics Engineer and one of their hot shoes. He's also the guy that designed the traction control system on the Viper. He says a different size tire (front or rear) will make the system think that one axle is slipping due to the speed difference of the wheel relative to the standard size. He says it will also effect ABS not just ESC and traction.

[TrackAire]

I got this directly from Erich Heuschele, SRT's Vehicle Dynamics Engineer and one of their hot shoes. He's also the guy that designed the traction control system on the Viper. He says a different size tire (front or rear) will make the system think that one axle is slipping due to the speed difference of the wheel relative to the standard size. He says it will also effect ABS not just ESC and traction.

It would really be nice if SRT or somebody could offer some computer code modification to allow for different sized tires than stock. The problem is the car thinks you're hitting ice (due to the now slower turning front tires) and the brakes may NOT activate when you need them (like coming into a hairpin at high speed on the track). On the C5 Corvettes this is called "Ice Mode" and it makes the pedal very hard and limits front brake pressure. You have to release and then re-apply the brakes to get it to try and go back to normal....yeah, real fun assuming you stay on the track.

This could so easily be fixed with a re-program, even via the dealer if SRT would allow it.

[ek1]

That shouldn't be a worry since ESC should be either in track mode or full off at the track. If you leave it on, you end up cooking your rear brakes...

I think what's going to happen is you will spend 100% of the time driving with the yellow "slip detected" warning light activated, on or off the track.

Having said that, I think this is a myth because my front tires (Hoosier R7 295/30/19) are approx 1" taller than stock Kumhos and yet I never had any traction control issues ever since I put them on.

[TrackAire]

I think what's going to happen is you will spend 100% of the time driving with the yellow "slip detected" warning light activated, on or off the track.

Having said that, I think this is a myth because my front tires (Hoosier R7 295/30/19) are approx 1" taller than stock Kumhos and yet I never had any traction control issues ever since I put them on.

On my Vette everything works normal (I run with all traction control off) except the ABS can activate and not allow full front brake pressure. This will only happen at full on track speeds under track braking situations. Has any body with a Gen 5 noticed a hard pedal when running a taller than stock front tire when going all out on the track? I'm not sure on the Viper how much percentage difference the front tire to rear tire height has to change before the ABS freaks out.

If no track rats have found this to be an issue, maybe the Gen 5 is not sensitive to the tire size difference and allows ABS to function correctly.

[Arizona Vipers]

I have run tires over 1" shorter in the rear and also 1" taller in the front than stock on both my 2016 ACR and 2013 track car. I have put thousands of extremely hard track miles on both of these cars trying every option of tire possible out there. There has never been and never will be a problem with the traction control on a 1" variance of tire.
Like I've said before, just having tire pressure too low vs too high can vary the diameter of a tire an inch. The manufacturers know this when developing the traction control software, you need much more variance of 1" to cause traction control issues.

[mjorgensen]

I got this directly from Erich Heuschele, SRT's Vehicle Dynamics Engineer and one of their hot shoes. He's also the guy that designed the traction control system on the Viper. He says a different size tire (front or rear) will make the system think that one axle is slipping due to the speed difference of the wheel relative to the standard size. He says it will also effect ABS not just ESC and traction.

I'm starting to believe that this was all in an effort to make us use only the Kumhos since SRT doesn't like it when you actually change their product from what it was engineered to be, glad it is working for some of you because we are always going to need options beyond the stock tires down the road especially.

[ViperGeorge]

I'm starting to believe that this was all in an effort to make us use only the Kumhos since SRT doesn't like it when you actually change their product from what it was engineered to be, glad it is working for some of you because we are always going to need options beyond the stock tires down the road especially.

Well, when I ran 315/30/18s on the front of my TA with 345/30/19s in the rear my ESC was freaking out. This was at Hastings and the car could not be driven with the ESC on, even to the gas station a 1/2 mile away. Haven't tried a significantly different tire on the ACR though.

[mjorgensen]

Well, when I ran 315/30/18s on the front of my TA with 345/30/19s in the rear my ESC was freaking out. This was at Hastings and the car could not be driven with the ESC on, even to the gas station a 1/2 mile away. Haven't tried a significantly different tire on the ACR though.

That was strange George, but I don't remember Nambo's 1st TA giving us any trouble at COTA with that combo so not sure what to think unless it is a variance in calibration car to car??? Weird.

[Nambo]

That was strange George, but I don't remember Nambo's 1st TA giving us any trouble at COTA with that combo so not sure what to think unless it is a variance in calibration car to car??? Weird.

I did not experience any issues with that setup on the TA Mark. ESC worked just fine in track mode, never tried any other mode other than off.

[ViperGeorge]

I did not experience any issues with that setup on the TA Mark. ESC worked just fine in track mode, never tried any other mode other than off.

With ESC off I did not experience any issue. I did not try track mode. Going to the gas station though I left it full on and the car would not go. I thought I was having some engine issue until I noticed the ESC light (sliding car icon) on the dash flashing. I turned ESC off to come back from the station and all was well. So Erich's comments made sense to me. Erich did say that turning off ESC would not change the effect that different tire sizes could have on the ABS system. There was no way to alter that impact. He did not say how different tire sizes could be before there was a noticeable impact. The 315s in the front definitely caused it in my TA.

[Pist0n]

I have run 315/30/18 NT01's on the front for five track days, 12 AutoX's, and 1,500 street miles and I have had zero issues. Two of the track days were in the wet and traction control was on during that time and working as intended.

[PkB2014]

I have run 315/30/18 NT01's on the front for five track days, 12 AutoX's, and 1,500 street miles and I have had zero issues. Two of the track days were in the wet and traction control was on during that time and working as intended.

Interesting thing is that the 315/30r18 NT01 have a diameter (25.35") that's almost identical to the 295/30r18 Hoosier A7 (25.3"). But you would need to know the Rear tire diameter as well to make a proper calculation and comparison. And then as someone mentioned the wear and PSI would also affect the real world diameter.

[FrankBarba]

Track Tires = Hoosiers, no other substitute. You will enjoy your track days.

[Pist0n]

Interesting thing is that the 315/30r18 NT01 have a diameter (25.35") that's almost identical to the 295/30r18 Hoosier A7 (25.3"). But you would need to know the Rear tire diameter as well to make a proper calculation and comparison. And then as someone mentioned the wear and PSI would also affect the real world diameter.

I run the ACR 355/30/19 Kumhos in the rear. I have a 2013 GTS, so I am not sure if that is the difference.

[PkB2014]

I run the ACR 355/30/19 Kumhos in the rear. I have a 2013 GTS, so I am not sure if that is the difference.

That would keep you between 1%-1.75% difference from stock, these other setups with Hoosiers would be in the 3%-4.5% difference range. I want to say I read somewhere about what percentage change from stock most system could handle, but I don't remember the numbers. But it sounds like under 2% doesn't seem to be an issue, and over 4% seems to be an issue.

[Smokin]

So is the consensus that you can change the fronts to a 295 30 R 19 but need to refrain from matching the backs to a 345 30 r 19 if you still want traction control for street use?

[jo_ker]

Stradman,

Which tires do you use within EU? (as long you UK guys are within the EU :z: :D )

original dimensions:
295/25 ZR19
355/30 ZR19

Michelin Cup2 would be available in:
295/30 R19
345/30 R19

i have good experience with the Cup2 on the 991GT3RS.

more air in the front tire would be also helpfull what i read and heared.
and ride height adjustment is important. clear on an aero car.


i´ve spoken also with Kumho Motorsport in Meuspath at the NOS... currently not able to get the V720 ACR. and for EU so or so not legal.
he will ask how Kumho plans it in 2018... as long more and more ACR´s are within the EU...

[stradman]

Stradman,

Which tires do you use within EU? (as long you UK guys are within the EU :z: :D )

original dimensions:
295/25 ZR19
355/30 ZR19

Michelin Cup2 would be available in:
295/30 R19
345/30 R19

i have good experience with the Cup2 on the 991GT3RS.

more air in the front tire would be also helpfull what i read and heared.
and ride height adjustment is important. clear on an aero car.


i´ve spoken also with Kumho Motorsport in Meuspath at the NOS... currently not able to get the V720 ACR. and for EU so or so not legal.
he will ask how Kumho plans it in 2018... as long more and more ACR´s are within the EU...

Hi Joker,
I got the Kuhmo's shipped from the USA through JonB. I usually got a dozen at a time-great service and price. Of course I pay customs for these. Even with customs they come out to about the same price as buying Trofeo's here in the UK.
Howver as I have a couple of sets of wheels, I am thinking of getting Hoosiers put on(we can find those in the UK) at least for the front, from the new season- as Kumhos don't last that long unfortunately. Haven't tried Cup2's on the car although this is possible-one ACR owner I know from Estonia who was at the Ring with me I know used these on the front . However I suspect they won't last too long either.
The plan is then to put 295/30/19 Cup 2's on the front so I can drive to the circuit and then change the fronts to Hoosiers R7's on the track. I will adjust the height with the Cup 2's as these will be about the same height as the Hoosiers 295/30/19 so I can swap easily. In the rear I will keep the Kumho's as they seem to last for about 3 track days. Btw I the V720 Kumhos are different to the Kumhos made especially for the ACR. I do not expect the ACR Kumhos to ever come to the EU as car was never exported outside the USA and Canada.

Btw let me know when you get car so we can stay in contact. In fact its probably a good idea that all ACR-E owners in Europe should stay in touch.

[jo_ker]

thank you stradman for your experience and your plan!

looking forward to join you in 2018 once - as soon the ACR arrived in one piece.
and i will come back to you as soon the car is ready. or as soon i need tires :)

[PkB2014]

I know the ACR is different, but I finally tried out my Hoosier track setup with my TA Group GTC and had no issues with Traction control intervening on the road.

Hoosier 315/30r18 & 345/30r19