Gary Javos Viper ACR Track Setup Thread

[Gary Javo]

I've decided to start this thread as a record of my track experience with this new car. I've read a lot of pointers from this board, and I set the car up with what I thought was a good starting point. I set the shock settings and ride height up according to the ACR book. I corner balanced (on a completely level surface) the car and it was within 20lbs between cross section combinations. I decided after reading about the inner front tire destruction to back off on the front negative camber a little. My alignment was Front: .07 degrees of toe each side, 6.0 degrees of caster, and -2.4 degrees of camber. Rear: .08 degrees of toe each side, -1.7 degrees of camber.

9-30-16 Roebling Road Raceway
When I got to the track, the idea was to slowly start feeling the car out. I have over 1000 laps at my home track, but I wanted to take this very slowly. I took the car out to get a little heat in the tires, and I was immediately shocked at how planted the rear was. It was immediately obvious that understeer was going to be the issue of the day. After three laps, I was shocked to see a 1:17.4 on my lap timer. That is cooking for a street car at this track. I brought her into the pit area and bled the pressures back down to the recommended 35 front 29 rear. I've always found that lap times are best in the morning, so I didn't expect to see any huge gains as the day went on.The first session consisted of 9 laps. Three of them being either warm up, cool down, or pit to set the lap timer.

I went out for the second session with a warm up lap and four hot laps followed by a cool down lap. Best lap time was a 1:16.8. I was starting to feel more comfortable with the car. I made an effort to establish where the understeer point was and back the steering angle down just a bit to keep from cooking the tires.

The third session was during the hottest part of the day. I had a passenger in the car and did a warm up lap, three hot laps, and cool down resulting in another 1:16.8. Once I got home and inspected the car, I noticed three small chunks of rubber missing from the outer band of the front left tire. Roebling is particularly hard on the front left. I am going to try to combat this by increasing the from negative camber to -2.8. I think I'm going to be a little more regimented with my sessions, sticking to a warm up lap followed by just two hot laps.

I also did not remove any of the hood vents or fender vents. I have another track day in two weeks. I'm going to replace the tire, realign with the new specs, and remove all of the hood vents. Are there any other suggestions for adjustments that will result in increased oversteer? I find it frustrating to not have the ability to rotate the car with the throttle. This lack of turn in is certainly leaving a lot on the table out there. I see that a lot of guys are working towards a better wheel tire combo, but the appeal of this car to me is that it can run these numbers in showroom stock condition. I want to explore the limits with the factory hardware.


https://youtu.be/eyEQwd4sGB4

[ViperGeorge]

This is a great thread. You're being very scientific about your setup and testing. Well done and keep the data coming.

[Pappy]

Excellent. Did you record any front tire temps?

Pappy

[Gary Javo]

No. I have a pyrometer, but left it home. I'll be sure to record that data next time.

[racegate]

Good stuff Gary, thats flying at Roebling for your first time out. Getting a tire pyrometer for the next track day was going to be my suggestion.

I'm not sure how much you are going to be able to get the car to really rotate with the throttle and be fast. The Viper does not like to be driven with a lot of slip angle in the rear due to the rear differential characteristics and suspension setup.

Do you have a Pbox?

[Gary Javo]

Yes. That's what I recorded my lap times with. Here is a picture of the front left tire.
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[99RT10]

Gary,
Where do you sign up?, PM me!!! Great post!!!

[ViperGeorge]

I gotta say one of the reasons that I have not bought an ACR is how fast they seem to burn through front tires. What gives?

[ek1]

Gary - the pic of your tire matches mine exactly ( I posted pics a few weeks ago).

Several people on this forum recommended decreasing the wing attack angle from Position 2 to Position 1, which should decrease rear downforce. I am going to do that for my next track weekend in 2 weeks.

Definitely take out all the fender and hood vents. This increases front downforce, although for me it did not make any difference in tire consumption.

I believe I saw a post when someone went to -2.8 camber in the front and it started destroying the inside of the front tire. I am running -2.6 in the front, which seems to be in the middle between not enough and too much.

As far as tire pressures, I have been given a recommendation of 25 PSI cold all around and 32-34 PSI hot all around. During my last event I started out with 32 PSI cold all around and aired down twice back to 32 PSI hot, but I still destroyed both front tires in less than a day.

[TrackratViper]

I am running -2.8 and am having the same tire problem. The inner side of the tire is wearing fine even with that much camber. The outside of the left front is generally the issue. At Barber Motorsports Park a couple of weeks ago, my left front was gone after a day and a half. Admittedly Barber is hard on the left front but this is ridiculous. When I got the car early in the year I started out with 25 psi cold. I have gradually increased Front tire pressure into the low thirties but it does not seem to make any difference. Previously I had a 2014 TA with Hoosiers and I could get several weekends out of them. Anybody have any ideas on how to correct this or tire alternatives for the track. I am not sure the Hoosiers can handle all of the downforce as they are a much lighter tire than the Kuhmos.

[ek1]

What I have read on this forum so far indicates that SRT essentially put "hero" tires on the front. They are great for setting lap records, but sacrifice themselves in less than a day if you drive balls out.

I had this perfect dream of driving the ACR to the track, driving on the track and then driving back home. In fact, I bought it to avoid dicking around with a dedicated race car and a trailer. Now, I already had to buy a 2nd set of front wheels with Hoosiers and arranged for someone to trailer the car to the Glen and back (in case I destroy both the stock Kumho's and Hoosiers over 2 track days). Dream shattered :)

I am trying 295/30/19 Hoosier R7s in the front at the next event. Who knows, I may even get one full weekend out of them.

Also, use the search feature. There are many threads about this issue, with lots of good info.

[Gary Javo]

Thanks elk. I am interested to see your results on the Hoosiers up front.

[SnakeWatching]

......I had this perfect dream of driving the ACR to the track.

I have never owned an ACR (would love to some day). Wasn't that the purpose of owning an American Club Racer - to drive it to the track and back?

Is the Gen 5 ACR so brutally fast that it can't be used that way? (compared to Gen2-Gen4 ACR).... (until a tire can be made that can "Take it")

[Gary Javo]

I've been trying to wrap my head around rebound/compression settings on the shocks. I'm experiencing substantial corner exit understeer. I've read a few articles on all of the techniques that each "expert" uses, but some of them contradict each other.
This is what I just read for rebound:
For understeer at corner exit: Turn the front shocks 2 clicks towards closed. Drive it again, and repeat if the condition continues to exist. If you get to fully closed and it still occurs you'll need to soften the front bar, stiffen the rear, add more front camber, or check your tire pressures. You might have to experiment with both because it may depend on many things.

And for Compression:
After rebound adjustment is complete, set all four dampers at 6 clicks from fully closed. Follow the procedures listed in the above section to determine where this is on the adjustment range. As you drive notice several things:
1. Do you feel the car skipping over bumps?
1. If yes, decrease compression on the end of the car skipping by two clicks.
Repeat as required.
2. Does the car put power down well on corner exit?
1. If no, increase compression at the rear of the car by two clicks unless the surface is bumpy. Repeat as required.
3. Does the car porpoise under braking?
1. If yes, increase compression of the front dampers by two clicks. Repeat as
required.

Then I've read that rebound doesn't effect understeer/oversteer nearly as much as compression. I'm really ignorant when it comes to these concepts, so I don't want to just start experimenting with all of these settings. Have any of you guys dialed any of this in any further?

[Gary Javo]

It seems like we are killing the front tires because of the understeer. We have a car with a pretty hefty curb weight being forced into the ground with substantial aero downforce dragging these soft front tires sideways through aggressive corners and it seems like we are simply pushing them right past their thermal limits causing de-lamination of the outer rubber layer. I feel strongly that if we can get more balance it will allow the car to yaw a little in turn shifting some of the grip load to the rear. Right now, the rear tires are not the least bit stressed. Lessening the rear spoiler angle will accomplish this, but I would rather increase front grip than decrease rear grip (for obvious reasons). It would be nice to talk to the factory guys that dialed these things in. I would love to pick their brains.

[TrackAire]

It seems like we are killing the front tires because of the understeer. We have a car with a pretty hefty curb weight being forced into the ground with substantial aero downforce dragging these soft front tires sideways through aggressive corners and it seems like we are simply pushing them right past their thermal limits causing de-lamination of the outer rubber layer. I feel strongly that if we can get more balance it will allow the car to yaw a little in turn shifting some of the grip load to the rear. Right now, the rear tires are not the least bit stressed. Lessening the rear spoiler angle will accomplish this, but I would rather increase front grip than decrease rear grip (for obvious reasons). It would be nice to talk to the factory guys that dialed these things in. I would love to pick their brains.

I think you're going to have to just settle for reducing rear traction via less down force so you can get the balance you want. I really don't think the front Kumho's can take more stress without wearing out even faster. So you're damned if you do, damned if you don't.....either understeer and wear them out or put even more traction against them and wear them out. To me it appears that there is so little sidewall for the amount of traction available that it just punishes the tires. Visually, they look small for the performance the ACR-E is capable of producing.

It will be cool to follow your progress and see what you come up with.

[VENOM V]

Gary,

Congrats and glad you are enjoying your new ACR. I'll throw in my $.02 after tracking for a while and getting perspective from fellow owners and the SRT engineers. Your car is under steering because you have tuned it for understeer. You are on the right track, here is what I suggest as a next step:

Increase front camber to -2.7 to -2.8, as you're thinking. I'd leave the rest of the alignment settings to ACR stock.
Tire pressure at the track should be about 33 psi hot, front and rear. I start at about 24 to 25 psi cold.
Remove vents in hood
Reduce wing to position 1. Still gobs of downforce at this position.
I am assuming you have the diffuser extensions and extreme splitter mounted

This car responds to trail braking. It's so stable with all of the rear aero that you can do this more aggressively than non aero cars with more confidence.

Not sure what I'm looking at on your front tire, but it looks like you went too hard before allowing tire to come up to temp. Maybe slow down on your first lap or two to let the heat come up deep in the tire. I've seen people delaminate and chunk them by going too hard too quickly.

The other thing to keep in perspective are your lap times, which you sound pleased with. At my home tracks, I have yet to have anyone challenge the ACR except for another extreme ACR. Yes keeping front tires alive is a challenge because of the extreme loading they see. However I've never driven an OEM tire that is anywhere near the performance of the Kumho. One forum member had two consecutive failures of Hoosiers on his ACR, a tire that has been flawless for many on other track cars (myself included). I am sticking with the Kumhos for now but may try Pirelli slicks in the future on 18" front / 19" rear wheels.

[lmcgrew79]

For the understeer either add more rake or stiffen front rebound.

[Eugene Lee]

great thread

[Gary Javo]

Yes, all strakes and diffeser extension installed. Thanks for the advice! Truly appreciated. I think I'll make the alignment and hood vent changes and see where we stand. I don't want to change too many things at once. I will also pay close attention to a gradual warm up. This thing is so much fun, I think I did jump the gun a little. I was adjusting the pressures to 35/29 hot but you had better results with 33/33 hot? I'll be sure to take the security hex wrench to take the rear spoiler down to position 1 on the fly.

[Gary Javo]

As far as lap times, yes, very pleased. I was 4 seconds a lap faster than any other car there that day.

[351carlo]

Great write up Gary. I believe any attempt to increase front grip will further exaggerate the lateral force applied to the tire, causing further delanination of the top tread rubber ply. Decreasing the load on the front tire, by allowing the back to unload laterally and not push the front, should alleviate the front tire delamination.

I'm still surprised to see the tire delaminating so regularly. There are some steps in compounding I would think they'd take to improve that. They may already be at the edge of what's possible.

Good luck. Some lap data with tire temperatures will help tremendously.

[ek1]

351carlo - several people here stated that delamination occurs due to overheating the tire, which in turn is caused by excessive scrubbing, which in turn is caused by lack of front grip. Are you saying that delamination occurs from excessive slip? I have destroyed plenty of front tires on other cars where outside edge was shaved off / destroyed due to lack of front downforce and grip, but I have never seen compound delamination on any tire before the Kumhos.

The big question is - does the tire become overheated due to scrubbing/slipping or due to sidewall flexing and generating heat?

[VENOM V]

Yes, all strakes and diffeser extension installed. Thanks for the advice! Truly appreciated. I think I'll make the alignment and hood vent changes and see where we stand. I don't want to change too many things at once. I will also pay close attention to a gradual warm up. This thing is so much fun, I think I did jump the gun a little. I was adjusting the pressures to 35/29 hot but you had better results with 33/33 hot? I'll be sure to take the security hex wrench to take the rear spoiler down to position 1 on the fly.


Yes it is! I can't wait to hit the track again, Laguna in November is my next event. The 35/29 f/r cold air pressures are for the street, the 35 protects the front wheel from potholes and the like. Tom O'Dell, one of the Viper engineers attended Viper Tracks 2 and advised that 33 psi hot is the sweet spot for these tires and cautioned not to go over 34 hot. He and Erich Heuschele told me to focus on not scrubbing the fronts, so I pay attention to ensuring I'm not turning the wheel more than tires can track. An indicator of scrubbing is if your front tire psi rises abnormally high. When starting at 24/24 cold, if my fronts exceed 34 psi I'm likely pushing them too hard. I've never had a tire blister although my friend had initially because he didn't warm them up enough. Still, my fronts only last about five sessions when I am driving hard. I just decreased alignment from -3.0 to -2.8 on advice of Luke (lmcgrew79). I may go to -2.7 if this doesn't work well. I do a cool down lap after maybe five or six laps then go hard again. The Kumho reminds of the Hoosier A7- very fast but you need to ensure you don't overheat them.


Erich also cautioned me to not go too stiff on the front damping or it'll kill the fronts. The ACR manual's recommended settings are pretty awesome as you've found.




As far as lap times, yes, very pleased. I was 4 seconds a lap faster than any other car there that day.

Yea that mirrors my experience. This thing is a rocket. Enjoy it!

[ViperGeorge]

So as someone that has considered trading my TA 2.0 in on an ACR-E I have a question for you guys that track an ACR-E. Do you think the extra speed you are seeing in an ACR is worth the price of new tires every track day?

Certainly an ACR-E would be faster than my TA 2.0 but I don't want to have to buy new front tires for every track day. As it is my TA is faster than all but dedicated race cars at my home track. I run Hoosier R7s on my TA (315 front and 345 rear) and I have 11 sessions on them so far. While they are wearing they still are good for several more sessions. My home track is High Plains Raceway here in Colorado and it has two uphill right turns that are particularly rough on left front tires. It also has a high speed straight (146mph) that leads to a high speed right turn. None the less, the Hoosiers are still holding up (yes, I do rotate them). With an ACR-E it seems the down force is contributing to excessive tire wear. My 09 ACR never went through tires like most of you guys with Gen 5 ACRs are doing.

[lmcgrew79]

So as someone that has considered trading my TA 2.0 in on an ACR-E I have a question for you guys that track an ACR-E. Do you think the extra speed you are seeing in an ACR is worth the price of new tires every track day?

Certainly an ACR-E would be faster than my TA 2.0 but I don't want to have to buy new front tires for every track day. As it is my TA is faster than all but dedicated race cars at my home track. I run Hoosier R7s on my TA (315 front and 345 rear) and I have 11 sessions on them so far. While they are wearing they still are good for several more sessions. My home track is High Plains Raceway here in Colorado and it has two uphill right turns that are particularly rough on left front tires. It also has a high speed straight (146mph) that leads to a high speed right turn. None the less, the Hoosiers are still holding up (yes, I do rotate them). With an ACR-E it seems the down force is contributing to excessive tire wear. My 09 ACR never went through tires like most of you guys with Gen 5 ACRs are doing.

I dont think the aero is wearing the tires as most turns are a track sub 80 mph and there is only about 400 lbs of downforce on the car at 80 and a probably 60% of that in the rear. Not nearly as many people pushing or understeering through the really fast turns. I think the acr on equal tire may be around 2 seconds a lap faster than the ta on equal tires. Im still probably driving the car with its mechanical grip and not as much on the aero grip in the fast stuff, which is really hard to do. I think what is wearing the kuhmo tires is one they are like gumballs and two the suspension is stiffer causing the tires to do more work. Ive said it before but after a few laps the car will start to push, imo because the tires start to get over heated. That being said they was still almost as fast as slicks but i had to really back off and trail and over slow the turns on entry to make sure it didnt go to steady state of push, which it will.

[lmcgrew79]

Great write up Gary. I believe any attempt to increase front grip will further exaggerate the lateral force applied to the tire, causing further delanination of the top tread rubber ply. Decreasing the load on the front tire, by allowing the back to unload laterally and not push the front, should alleviate the front tire delamination.

I'm still surprised to see the tire delaminating so regularly. There are some steps in compounding I would think they'd take to improve that. They may already be at the edge of what's possible.

Good luck. Some lap data with tire temperatures will help tremendously.

I would probably agree to this other than you may be decreasing the rear grip to compensate for the loss of front grip, aka more neutral, you need to fix the end that is causing the problem, add more rake or front rebound may cause even more front tire wear though, they obviously made the front tires softer than the rear which is great for turning 3 hot laps or even autoxing, but not for a weekend worth of 30 min sessions, but that isnt a problem either as long as you bring extra tires. At 3.0 degrees front camber i toasted the inners in one day at mid ohio which is easy on tires. At 2.7 degrees i probably used 80 percent of the tires up in the next day. The rear at 1.8 seems to be the ticket. The fronts im not sure Even with racing slicks my front driver side tire wore really even at 2.7 but i got much more wear on the passenger side inside as pitt race is dominantly right turns, and i should have swapped the front tires after day one. I may go to 2.5 and see if that helps. At pitt race i ran about 1.75 degrees of rake instead of the factory 1.5 may have been slightly to much as i had tons of front grip and not as much rear on exit, but i was also on some wore out rears. I would rather have the car slightly loose than tight, but that is preference. Just sharing my input as im sure different driving styles may like different setups.

[ViperGeorge]

I dont think the aero is wearing the tires as most turns are a track sub 80 mph and there is only about 400 lbs of downforce on the car at 80 and a probably 60% of that in the rear. Not nearly as many people pushing or understeering through the really fast turns. I think the acr on equal tire may be around 2 seconds a lap faster than the ta on equal tires. Im still probably driving the car with its mechanical grip and not as much on the aero grip in the fast stuff, which is really hard to do. I think what is wearing the kuhmo tires is one they are like gumballs and two the suspension is stiffer causing the tires to do more work. Ive said it before but after a few laps the car will start to push, imo because the tires start to get over heated. That being said they was still almost as fast as slicks but i had to really back off and trail and over slow the turns on entry to make sure it didnt go to steady state of push, which it will.

You may be correct. Certainly the Kumhos are gumballs but JD in his ACR-E went through a set of Michelin slicks in one day at Hastings Motorsports Park. They would typically last longer than a few sessions. I believe he put the Kumhos back on and then toasted them the following day. Either way, unless someone comes up with the optimal setup on an ACR-E it seems they will eat tires much more quickly than my TA. With headers, underdrive pulley, Hoosiers, and Arrow Controller my TA 2.0 has more HP than a stock ACR which may help it overcome the ACR's aero advantage a little although probably not completely. I love the look of the ACR-E but I couldn't stomach buying all the tires it would eat. Not to mention that tire choices in 19/19 sizes for the car are really limited (like non-existent).

I've actually been looking for a reason to go with an ACR but haven't yet convinced myself it makes sense.

[plumcrazy]

Gary, good to see you made it here. welcome !

[VENOM V]

You may be correct. Certainly the Kumhos are gumballs but JD in his ACR-E went through a set of Michelin slicks in one day at Hastings Motorsports Park. They would typically last longer than a few sessions. I believe he put the Kumhos back on and then toasted them the following day. Either way, unless someone comes up with the optimal setup on an ACR-E it seems they will eat tires much more quickly than my TA. With headers, underdrive pulley, Hoosiers, and Arrow Controller my TA 2.0 has more HP than a stock ACR which may help it overcome the ACR's aero advantage a little although probably not completely. I love the look of the ACR-E but I couldn't stomach buying all the tires it would eat. Not to mention that tire choices in 19/19 sizes for the car are really limited (like non-existent).

I've actually been looking for a reason to go with an ACR but haven't yet convinced myself it makes sense.

Regarding tires, we've seen Kumhos, Hoosiers and Michelin slicks all struggle. In the hands of an advanced driver, the ACR is going to put more stress on tires, which isn't surprising seeing how the corner speeds are higher than probably any production car made. The only front tire I know of that has held up longer than about a day is the Pirelli slick on Luke's ACR after he reduced the front camber to -2.7. The compromise is that you have to run 18" fronts and clearance is tight if you have CCMs. Luke, jump in here if you have any more to add.

[allans]

As said above 33/33 HOT is a good target. I drive mine at least 5 laps (10miles) to warm them up slowly, it seems to really help. I'm at 2.5 front camber and soft on compression and stiff on rebound. All of this with trail braking has really helped with front tire "damage". Best, Allan

[351carlo]

Regarding tires, we've seen Kumhos, Hoosiers and Michelin slicks all struggle. In the hands of an advanced driver, the ACR is going to put more stress on tires, which isn't surprising seeing how the corner speeds are higher than probably any production car made. The only front tire I know of that has held up longer than about a day is the Pirelli slick on Luke's ACR after he reduced the front camber to -2.7. The compromise is that you have to run 18" fronts and clearance is tight if you have CCMs. Luke, jump in here if you have any more to add.

Not only are the corner speeds high for a production car, but the downforce and weight of the car are high relative to other cars. You've got a very high buildup of heat due to hysteresis - the high hysteresis, soft tires build up a lot more heat. When this heat is generated and the tires scrub, the rubber delaminates.

Running a tire 60 mph with 3500 pounds on it generates some heat. Running that same tire at 60 mph with 4500 pounds on it generates much more heat. Even in a straight line you're building up heat in the tires with the ACR.

Just my opinion though...

[Gary Javo]

Thanks allans. I had no idea you need to build heat over such a time period. I'll give it a try on the 14th and see if that helps. Please keep the advice coming. It will be great to continue building our knowledge base on these great machines.

[ViperGeorge]

Regarding tires, we've seen Kumhos, Hoosiers and Michelin slicks all struggle. In the hands of an advanced driver, the ACR is going to put more stress on tires, which isn't surprising seeing how the corner speeds are higher than probably any production car made. The only front tire I know of that has held up longer than about a day is the Pirelli slick on Luke's ACR after he reduced the front camber to -2.7. The compromise is that you have to run 18" fronts and clearance is tight if you have CCMs. Luke, jump in here if you have any more to add.

Understood. The question is though are the 2 seconds or so that an ACR is faster than the TA worth it given the cost of tires? Also why didn't the Gen 4 ACRs burn up tires? Ok, not as much down force but still a lot. And if a Gen 4 ACR ran the Kumhos how much slower what it be than a Gen 5 ACR? Some of the difference could come down to the additional HP of a Gen 5 don't forget.

[VENOM V]

Understood. The question is though are the 2 seconds or so that an ACR is faster than the TA worth it given the cost of tires? Also why didn't the Gen 4 ACRs burn up tires? Ok, not as much down force but still a lot. And if a Gen 4 ACR ran the Kumhos how much slower what it be than a Gen 5 ACR? Some of the difference could come down to the additional HP of a Gen 5 don't forget.

Those are all great questions, especially the one about whether it's worth it. I guess it depends on your personality. I have serious track rat friends that don't feel the need to be the fast guy. Others that are naturally competitive get tremendous satisfaction out of it. For me, my GTS was often one of the fastest on a given track day, but the ACR just takes it to a new level of confidence and in my case enjoyment. Nothing like beating highly modded, high HP winged Corvettes and Porsche cup cars on slicks with a bone stock Dodge down to the tires and brakes. I cannot think of a single thing in life that I can do with my clothes on that is more fulfilling than tracking this beast. For this reason, I'm ok with paying more for consumables, others may not be.

I think it eats tires more than the Gen IV ACR because they found a winning combo of suspension tuning, brakes, aero Etc that hasn't been achieved previously. All that energy of those high speed corners has to go somewhere, and as Carlo said they also have to contend with hefty weight and aero. Light for a street car but heavy for a race car.

[MomentaryRacing]

This sounds like a combination of balance issue between front and rear grip, and possibly driving style. Telltale sign is that the issue starts to occur when at least some tires come up to temp, and that it's a steady state, not transient state issue.

Does not sound like damper setting or rear wing have much to do with this, if we are talking about steady state / exit / on-throttle underseer

Without driving data, or at least a video, hard to diagnose.

Some suggestions:

Check your front vs rear tire temps (lacking pyrometer, start them at same pressure, drive until you experience the issue, come in and check which ones added more pressure), if fronts are consistently hotter, you may be overloading them under braking (this would be technique/style thing and/or possibly front downforce). Does the track have multiple hard braking zones stacked up without long straights in between?

Are you pretty tight to the apex and then the car starts to push, or does the issue begin before you are at the apex?

If you carry more braking into the turn, is it better/worse?

If you add some entry speed, is the issue better/worse?

You listed your front toe setting, did not mention if it's out or in. May be worth setting it to 0 if the wear is concern.

[MomentaryRacing]

Re: get4 ACR - In stock trim, with factory recommended "track" settings and OEM Pilot Sport Cups, Gen4 ACR can be pretty hard on the tires, depending on the track.

[Bruce H.]

I've never seen tire temp data posted in any of these discussions. Does anyone have tire temperature data they can post from using a pyrometer, along with the setup they were running? Looking at tire pressure and wear patterns just aren't adequate for doing set up if you don't know temps across the tire.

[mjorgensen]

We ran JD's car this weekend at COTA with the 19/18 Michelins and they worked great. Tire wear was nearly perfect and they still looked great after 2 days. We made a couple MCS shock adjustments and set the wing to position #1 which helped I'm sure. Tire pressures came up even front to rear, no temps sorry. The 30 series front tire has almost a 333mm section width so much more tire to work with.
woodhousemotorsports.com

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[Nambo]

The Michelins don't like a lot of camber either, 2.5 seems to be a good number for them. Backed of the front rebound a couple clicks and started at 26 psi cold and they came up as planned to 32 psi and stayed there for the 25 minute session, no need to bleed pressures during the session. I have 23 sessions on the rears and they still look great, 8 sessions on the front and they look to be good for at least that many more. My previous experience with the short tire life was a direct cause of a poor surface at that track.

This is just an observation that worked for me on turn in. Car really responded (for me at least) by very hard late braking, dropping gears and keeping the RPM's over 4,000 on corner entry and aggressively throttle steering the car through the turn. Requires a lot more effort and concentration but the car rewarded me greatly by doing this. Push went away and turn in became razor sharp, just be easy with that right foot! Set my personal best of a 2:27.1 this weekend, gonna keep pushing to get down to low 20's. I'll see if I can figure out how to post my AIM video.

[VENOM V]

Mark and Nambo,

That's promising about the Michelins, I think that mirrors Luke's success with Pirellis. As Nambo pointed out, a lot of folks are migrating to less front camber as you have proposed. What was JD's camber?

Nambo, very hard late trail braking is being taught by Bondurant, and Chris Winkler and Erich Heuschele also were recommending it to reduce scrubbing. I'm going to do it more aggressively. The rear is so damned planted and stable that the car can handle it.

[Nambo]

Todd,

JD is me (Nambo), should have used a more obvious screen name... My camber is at 2.5.

[VENOM V]

Oh haha, well good deal. An advanced driver like you paired with Mark is a winning combo. Keep us posted as you learn more.

With the success you and Luke are having with slicks, I'm ready to spring for 18s / 19s. Just need to choose between Forgeline and Finnspeed. I'm planning on starting with Pirelli DH slicks then I may try the Michelins.

[Nambo]

I have to make a correction, too many alignment sheets in my Viper folder.... My current alignment with the Michelins is 2.8, not 2.5. The 2.5 was used with the Kumho's in an attempt to save their lives with minimal success.

[VENOM V]

I have to make a correction, too many alignment sheets in my Viper folder.... My current alignment with the Michelins is 2.8, not 2.5. The 2.5 was used with the Kumho's in an attempt to save their lives with minimal success.

Good, I'm at -2.8 now

[Gary Javo]

Great info. Thx for posting. What is a ballpark price for that wheel tire setup? I assume they can withstand a short drive to the track right?

[Nambo]

Great info. Thx for posting. What is a ballpark price for that wheel tire setup? I assume they can withstand a short drive to the track right?

It would actually be illegal since they are competition slicks but you could if it was a very short distance and the roads were in good condition. It would be easy to ruin one and they aren't cheap. I buy my tires from a store online and they cost $2400 for the set heat cycled and shipped to my door (pm me for the name as they are not a site sponsor).

There are several places to get the Forgelines, I bought mine through Mark J at Woodhouse but Tony (Nineball) at Deviate Motoring is another good source. I paid north of $5,500 for the set.

[Arizona Vipers]

We made a couple MCS shock adjustments and set the wing to position #1 which helped I'm sure. Tire pressures came up even front to rear, no temps sorry.
woodhousemotorsports.com


Great pics! Are you running the 2 way or 3 way MCS shocks? What did you end up setting them at?

[Arizona Vipers]

I'm ready to spring for 18s / 19s. Just need to choose between Forgeline and Finnspeed.

I heard a couple days ago that Finspeed is involved in a business lawsuit and their production is currently frozen.
I had my order for my 2nd set of 18/18's canceled until further notice. I think I'm going to try Forgeline's for my 2nd set. They should be within 1lb a of each other per wheel.

[lmcgrew79]

I've never seen tire temp data posted in any of these discussions. Does anyone have tire temperature data they can post from using a pyrometer, along with the setup they were running? Looking at tire pressure and wear patterns just aren't adequate for doing set up if you don't know temps across the tire. I've checked the temps on the pirellis only after a cool down lap which isn't the right way of doing it. Seems the acr wheel is offset more than the ta, wonder if the positive scrub radius has any effect on the tire wear? Another thing I've thought about on the kuhmo, is the tire has such a low profile, maybe it affects the tire contact patch and is even more prone to a perfect front setup? IDK i'm just throwing stuff out there for people that know more than me maybe it means nothing. Regardless i think mine is all camber/toe wear and will try to swap front lefts and rights after one day for now on.

[Bruce H.]

Thanks Luke. I suspect hot lap temp monitoring will reveal too much camber, and be a useful tool to use in individual's setups. This was my findings on the TA when examining tread wear actually led to the opposite and wrong conclusion, at least in my track experience. SRT generally seems to be big on recommending a lot of negative camber from what I've heard and read, but I think individual needs may vary considerably.

[Gary Javo]

I went back to the track on October 14th. I was by myself so I didn't get any tire temps. I increased the front negative camber to -2.8. I also decreased the rear spoiler angle to factory position 1. I made sure that the hot tire pressures were at 33psi all the way around. I also removed the fender gills, but left the 6 small hood vents in place because they seemed like a pita to remove. These adjustments certainly were a step in the right direction. The car still under steers, but not nearly as bad. It's much easier to get the car to turn in with these settings. My lap times imoroved. Best lap of the day was a 1:15.5. I was 5 seconds a lap faster than any other street car there. During each of my four sessions I had two warm up laps followed by two hot laps. With this technique, the front tires lived. Woohoo.

Here is a video of a slower shakedown session earlier in the day.

https://youtu.be/5shyn979zJY

[jpgunn123]

Ran my ACR at Chuckwalla (http://goracecvr.com/track/) (lots of turns, but not super high speed -- 83.2mph average) in Southern California this past weekend. This was my first time on a Road Course with the ACR (been doing AutoX on the coast to avoid heat all summer). I ran with the PCA San Diego Region, and we had 120+ cars there. Ended up getting the third Fastest time of the weekend behind two Cup Cars with Turbos (unlimited GT1 class cars). The temperatures were in the mid 90s both days with cooler sessions in the mornings (80s).

I started with my setup for AutoX where I had been running A7 Hoosiers in 335/30/18 (on 12" wheels with 8 5/8" backspacing) and 345/35/18 (on 18X13 normal Offset). For the A7s I was 3.5 degrees front and the rear as delivered (rear is perfect at stock setup). For Chuckwalla I mounted R7s in the same sizes. Ride Heights were 102mm front and 141mm rear. I had been running 1 on compression and 7 on rebound in front for AutoX, and factory track spec rear (5/3). For Chuckwalla I decided I would set the front to the factory settings too (7/3). Tire pressures I started at 26 psi targeting 35psi.

So -- how did the initial setup work? Too much camber -- was seeing a 30 degree delta in the front when I temped. Tires rose too much in pressure -- went to 39/40 and got a little greasy. Car had some push on the lower speed mechanical grip corners (under 80mph). I was learning the track though and maybe not getting the optimum line every lap, but the evidence was there. I ran one more session (to insure I was not over driving the front and getting good lines) and took more pyrometer readings -- as pictured (ambient temp was 94).
20579

Camber was too much, and the tires would not be happy for long. Quick front end alignment was needed, so I took out .3 degrees from the front (taking it to -3.2) and set toe back to 1/8th out total. Dropped 5 psi from the tires while hot to bring the front to 35 and rear to 34.

The next session out I was able to find some clear track, and the changes were working. Tires weren't getting as greasy (still seemed a bit when the temps/pressures rose). Time improved 2.5 seconds from a 1:58.70 to 1:56.18. Car definitely felt more hooked up in the lower speed corners.
Here is the video from that run -- sorry it is shakey (and somewhat cropped -- not sure why Youtube does that) -- Need to improve the mounting setup for the Go-Pro. Using Harry's Lap Timer, 10Hz Gps, and the Kiwi 3 OBD-II.

https://www.youtube.com/watch?v=gb8Bx3nO9SI

At this point I didn't feel like messing with the alignment again (although it could use .3 less again). I went ahead and ran the next two sessions in the morning on Sunday. Temps in the first session were great, but the traffic was terrible and there was no good hot lap. Second session the ambient temperature was back to 92, and the track had less people on it. Managed to get out at the front and had a few clear laps to warm up the tires and throw down a lap with only 2 passes needed. Ran a 1:55.72 which was good, and got the following pyrometer readings.
20580

Some results:
20582

Tires were getting low enough on the inside of the fronts (and I drove 160 miles there on them and had to drive home), so I called it a day. Before I left, I changed the alignment to 2.9 front and 1/8 total toe. Seems like that will be the sweet spot. Maybe lower the front slightly How low have others gone? In looking back at some of the pictures from the track photographer, I can see the front inside tire is not sitting as flat as it could be if it had more caster. Here is a picture -- speed was about 80mph in this turn. What do you all think? What caster has everyone tried?
20581


I have 2 Private test days at ButtonWillow (got a garage too) in early November with 20 others, so I should have plenty of time to test. I will also be taking another wheel tire combination with me that I think will be a good compromise for better wear/street usage too. Using the factory ACR wheels and stock rear Kumho (355/30/19) and a 305/30/19 Bridgestone RE-71R in the front on the 19X11. I think this combination should be well matched. I hope to figure out the camber needed (hopefully happy at -2.8/2.9). This would be nice for practice laps and street use, and then throw on Hoosiers when you want. Would also like to try a set of BFG Rival-S on the 18s if I get a chance, but that may be too much to tackle.

[ACR Steve]

I am at 2.8 with 0 toe, stock track suggested shock settings, touch above track suggested ride height and corner balanced feels great very little push (understeer) . You guys that are getting push have to say where? entrance ,middle or exit?

If it everywhere you are way off.
Entrance work with the front of the car
Exit work with the rear
Mid corner lots of scenarios

Other thing to consider is if its pushing in fast corners or slow ? Right and/or left hand turns?

[mjorgensen]

pjgunn123,

Running toe out along with all that camber is what is killing inside edge. You also have a 1" wider wheel which could be increasing the scrub even more. The castor is generally around 6.3 if you are running -2.8 and less as that camber is taken to -3+. If you could get more castor you will be able to get away with less camber IMHO anyways and that is what I have always done. Every tire seems to need something different based on construction so even if it is dialed for one you will possibly need a change if trying something different or even a different size.

Toe out works great for autocross, but creates it's own problems at the track in my experience.

[jpgunn123]

I am at 2.8 with 0 toe, stock track suggested shock settings, touch above track suggested ride height and corner balanced feels great very little push (understeer) . You guys that are getting push have to say where? entrance ,middle or exit?

If it everywhere you are way off.
Entrance work with the front of the car
Exit work with the rear
Mid corner lots of scenarios

Other thing to consider is if its pushing in fast corners or slow ? Right and/or left hand turns?

Lower speed exit push (under 80mph). But it is not much (barely any, but I am picky). Going to run a little less pressure next time (33psi hot vs. 35), and I thought bringing the front down a little would help (or raising the rear). I ran 144mm rear ride height before with 102mm front and the car was very good.

[ACR Steve]

exit work with the back of the car
choices:
1)raise rear ride height
2) stiffen rear shock compression
Don't do both start with compression see if it helps. Easy fix

Other choices with springs and sway bars but I would leave that stock.

Make sure you are not turning in early . I don't know what experience you have on track however remember our cars turn in supper fast. It leads to many drivers even experienced guys turning in early and running out of road on the exit. make sure your line is exact not just in the approximate area. We are talking inches not feet

Hope this helps :)

[jpgunn123]

pjgunn123,

Running toe out along with all that camber is what is killing inside edge. You also have a 1" wider wheel which could be increasing the scrub even more. The castor is generally around 6.3 if you are running -2.8 and less as that camber is taken to -3+. If you could get more castor you will be able to get away with less camber IMHO anyways and that is what I have always done. Every tire seems to need something different based on construction so even if it is dialed for one you will possibly need a change if trying something different or even a different size.

Toe out works great for autocross, but creates it's own problems at the track in my experience.

Thanks Mark -- I did back off the toe to ~1/16th when I set the camber to -2.9 on Sunday before heading home. I will set it to 0 before my next AX and ButtonWillow. Do you think we should just max Caster once you are at -2.8 in the front?

[mjorgensen]

Thanks Mark -- I did back off the toe to ~1/16th when I set the camber to -2.9 on Sunday before heading home. I will set it to 0 before my next AX and ButtonWillow. Do you think we should just max Caster once you are at -2.8 in the front?

I don't think you are going to get more than +6.7 castor and that is probably about all you would even want to try James. There is always going to be a compromise and I have always wanted the tire as flat as possible early in the turn even if it means wearing more on the outside edge at the end of tire life. There is no reason at all that the inside edges should be wearing faster, but that is ONLY my opinion I realize that.

[jpgunn123]

exit work with the back of the car
choices:
1)raise rear ride height
2) stiffen rear shock compression
Don't do both start with compression see if it helps. Easy fix

Other choices with springs and sway bars but I would leave that stock.

Make sure you are not turning in early . I don't know what experience you have on track however remember our cars turn in supper fast. It leads to many drivers even experienced guys turning in early and running out of road on the exit. make sure your line is exact not just in the approximate area. We are talking inches not feet

Hope this helps :)
Steve,

The times I ran at Chuckwalla (first time there) are near the front of the GT2 pack for an SCCA majors race, or faster than the T1 record by 3 seconds. http://cdn.growassets.net/user_files/scca/downloads/000/007/234/15-majors-chuckwalla-results.pdf?1433437245

I am sure the next time I will be able to drop a second or more with more time. I am a bit rusty, but I am not over driving the car typically.

Also have won a couple of SCCA Solo2 National championships, and a Pro Solo Finale class and overall.

Used to race Spec RX7 in the early 1990s. Managed to set a track record at PIR, pole, etc.

[mjorgensen]

Steve,

The times I ran at Chuckwalla (first time there) are near the front of the GT2 pack for an SCCA majors race, or faster than the T1 record by 3 seconds. http://cdn.growassets.net/user_files/scca/downloads/000/007/234/15-majors-chuckwalla-results.pdf?1433437245

I am sure the next time I will be able to drop a second or more with more time.

Also have won a couple of SCCA Solo2 National championships, and a Pro Solo Finale class and overall.

Yep James is the real deal I've run with him in Solo2 and Pro Solo.

[ACR Steve]

cool so you know what you are doing no doubt. Try 2 clicks on rear compression see if it helps. Or as you said drop front pressure but leave rears.

[jpgunn123]

Thanks Steve.
Front to rear temps are looking good, and the car is working well at both ends where it is now. I am seeing 1.85 Gs in a couple of turns I think tire wear in the front could still be better, and backing off the toe and camber should help. Will drop pressure a couple of psi too.

[Jabba954]

One thing I've definitely noticed is that the tire pressures on the gauge are VERY slow to update, so if you're showing 32-33PSI on the dash, you're likely actually at 34-36 PSI. So now I keep an eye on indicated pressures, and if they reach 32 PSI, I come in immediately bleed out a few PSI. That has SUBSTANTIALLY improved the longevity of my tires, and evened out the wear a bit (the wear is certainly also facilitated by becoming a better driver).

My PR at Sonoma is a 1:45.2 now, bone stock ACR.

[Scotts-ACR]

Was at the Glen last weekend. Car was basically set up like the SRT video tells you to do. The car made so much rear downforce the front was getting light up the esses. Going to reduce the wing 1 position.

Im also finding the car's 5th gear is basically useless on the track. Shifting from 4th to 5th bogs. Hits a wall around 150 or so.

[Nambo]

Was at the Glen last weekend. Car was basically set up like the SRT video tells you to do. The car made so much rear downforce the front was getting light up the esses. Going to reduce the wing 1 position.

Im also finding the car's 5th gear is basically useless on the track. Shifting from 4th to 5th bogs. Hits a wall around 150 or so.

I have the same thoughts on 5th gear, pretty much useless on track. I know Calvo is swapping out 5th gear and I am interested in getting this done.

[mjorgensen]

I have the same thoughts on 5th gear, pretty much useless on track. I know Calvo is swapping out 5th gear and I am interested in getting this done.

Also working with Donato on a close ratio 5th gear option that is strong enough for the Viper.

[Scotts-ACR]

Also working with Donato on a close ratio 5th gear option that is strong enough for the Viper.

Sent ya an email earlier in the week. ;)

This is good news.

[Gary Javo]

Here is the vid of my fastest lap so far at my home track (and a personal best). I wound up running a 1:15.36. I just signed up for the Flatout Motorsports Daytona event in April so we will see how that goes.


https://www.youtube.com/watch?v=5Or5kS0jZQk

[allans]

Nice lap and nice car. Best, Allan

[Snorman]

Here is the vid of my fastest lap so far at my home track (and a personal best). I wound up running a 1:15.36. I just signed up for the Flatout Motorsports Daytona event in April so we will see how that goes.


https://www.youtube.com/watch?v=5Or5kS0jZQk
Gary,
See you at Daytona (if not before)! FoM are great friends of mine and I've done the Daytona-Rolex event for the last several years. FYI, there is also an Audi-Ohio event at Daytona in December. I can't make it due to personal obligations...same weekend as a great Sebring event with NIGHT sessions, and I love Sebring at night.
I'm heading down to Sebring tomorrow with Chin.
S.

[Gary Javo]

Sounds good. It will be great to get the ACRs together at the track. I think Andy is going to bring his white car as well.