Correct R7 sizes for factory 2017 ACR E Wheels

[CarbonDan]

Time to make the bump from V720s to R7s for my stock 19" 2017 ACR-E wheels.
Can someone please advise the correct size R7 to select, as well as provide any info on the height differences of the two tires?
My car is set to the factory recommended track height of 4.0 front, 5.5" rear and I'll have to make some adjustments to the ride height myself to maintain those same levels with the new tires.
Any help is greatly appreciated!

Also, what alignment specs would you run with Hoosiers?
I just had my car corner balanced and aligned for the V720s and they wear in inner fronts much faster than anywhere else.
I had asked for -2.8 up front. I got:
-3.0 front
6.5 caster
0.01 toe
0.00 steer ahead

-2.0 Rear
0.11 toe

[Racingswh]

295/30/19 f 26.1" dia and 345/30/19 r 26.8" dia as compared to 24.9" dia front and 27.5" dia rear

Sway bars need adjustable end links to properly corner balance the car. They do not come on the car from the factory.

Front should be 3 3/4" or so rear 5 1/4" or so. Corner weights are going to decide final ride height. As you can see you will need to lower the front to get to your ride height and possibly raise the rear to allow for the difference in tire heights.

Then the issue becomes front fender liner clearance and you have to decide if you want to sacrifice those in the name of performance or keep the car higher so you never have any rubbing. In any event with sticky tires sometimes they will pick up rocks and debris and projectile them through the fender liners so even at a higher ride height you may still see damage. Also I would put a protective edge around the fender openings and do not run the fender vents at the track for any period of time. They will get destroyed.

My ACR-E for whatever reason likes less camber in the front. 2.4 to 2.7 or it mows off the inside of the unloaded tires pretty quick. Right hand turn tracks it would scrub the inside of the right front tire off pretty fast. I think I ran 1.5 or something like that in the rear. Slight toe out in the front and slight toe in in the rear. A tire pyrometer gauge, preferably one that sticks into the tire rubber, really tells you what you need to know about camber.

[CarbonDan]

Wow thanks for the wealth of info as usual! (I've read many of your posts as I've been track prepping my car over the last few weeks).

I don't mind wearing through the fender liner, that could be replaced when/if the time came.

My issue with the v720s was exactly as you described, burned right through the passenger inner tread, exactly what I'd like to avoid.
I got the R7s ordered in the sizes you recommended, should be here Tuesday.

Now the important question:
I just had the car lowered to 4 & 5.5", corner balanced and aligned last week, for V720s.
I have a track weekend coming up this weekend and can't get on their schedule in time.
- Do you reckon I could make that ride height adjustment to compensate for the tire height differences myself at home, without throwing off the corner balancing too significantly? I'm still probably in around the phase of lopping off a full .5 to 1.0 second from my lap time per day with this car as I get used to the giant upgrade over my GT3 on track.
Hell while I'm at it, do you think I could adjust the front negative camber myself to pull .2-.4 out of that -3.0 without screwing it up too bad?

Here's an onboard video from yesterday, this is the track I'll be running all summer.


https://www.youtube.com/watch?v=X-8DRhVJOXY

[TA Two Oh]

I was only there once but I love that track. A 1:47 is great! And as you know, the R7's should shave some time for you. Not enough to catch Cable but other than that, you should be "the fast guy." My son is moving to the area (Redmond) later this year and wants to get into track driving. Luckily, like you, he'll have a nice venue close by.

[Black Pearl]

Where did you buy the R7's?

[Racingswh]

Wow thanks for the wealth of info as usual! (I've read many of your posts as I've been track prepping my car over the last few weeks).

I don't mind wearing through the fender liner, that could be replaced when/if the time came.

My issue with the v720s was exactly as you described, burned right through the passenger inner tread, exactly what I'd like to avoid.
I got the R7s ordered in the sizes you recommended, should be here Tuesday.

Now the important question:
I just had the car lowered to 4 & 5.5", corner balanced and aligned last week, for V720s.
I have a track weekend coming up this weekend and can't get on their schedule in time.
- Do you reckon I could make that ride height adjustment to compensate for the tire height differences myself at home, without throwing off the corner balancing too significantly? I'm still probably in around the phase of lopping off a full .5 to 1.0 second from my lap time per day with this car as I get used to the giant upgrade over my GT3 on track.
Hell while I'm at it, do you think I could adjust the front negative camber myself to pull .2-.4 out of that -3.0 without screwing it up too bad?

Here's an onboard video from yesterday, this is the track I'll be running all summer.


https://www.youtube.com/watch?v=X-8DRhVJOXY

Of course. I don't know much but I have done this a time or two.

When I first got the car I didn't have much time to prep before the first event so I literally just put tires on it and went after it. It was fine. It drug the strakes too much but as soon as I got comfortable with hearing that awful noise I was all good.

You can certainly try and adjust camber yourself but I always like to do mine on a Hunter machine or equivalent with the help of an expert alignment specialist. It's just so easy and accurate. For me I wouldn't mess with it myself before the upcoming event for fear that i make it worse than better. With that camber you have now you will wear the inside of the Hoosiers down quickly as well although they will last longer than the Kumho's. I always get flamed when I say this but in my opinion Kumho's on ACR-E's as track tires are complete garbage. Borderline dangerous. They work far better on a lighter car with no aero.

I know that Cable goes super quick with lots of camber but for me the tire wear trade off is never worth it. I do this for fun only, not lap records. When you get the chance to get it back to an alignment shop I would run - 2.4 in the front and see how the outside shoulders hold up for you. I would also run dead 0 toe in the front. It turns in plenty fast anyway. It really doesn't need any toe out.

When you can you need to get adjustable end links. Whoever told you they corner balanced your car if it does not have adjustable end links on the sway bars was telling you a story. A car is corner balanced with sway bars disconnected and drivers weight in the drivers seat. Sways bars are then connected and end links adjusted so there is 0 preload on the bars and corner weights remain the same after the bars are attached. Anyone who tells you any different is doing it differently than I have been taught. You can get away with it and on a car like the ACR-E it's still going to work amazingly well but it can be better.

So if it were me this is exactly what I would do. I would measure ride height at the front and I would turn the collars exactly the same amount on both side to get the front to 4". Then I would go to the rear and do the same thing to get it to 5.5". Then I would run it and see what happens keeping an eye on the insides of the front tires. When you have the time I would get it back to the alignment shop and have them readjust everything and take some camber out of it.

[Racingswh]

If the rear starts to dance around under braking add rebound until it stops, usually 2 or 3 clicks is all it needs.

[CarbonDan]

Of course. I don't know much but I have done this a time or two.

When I first got the car I didn't have much time to prep before the first event so I literally just put tires on it and went after it. It was fine. It drug the strakes too much but as soon as I got comfortable with hearing that awful noise I was all good.

You can certainly try and adjust camber yourself but I always like to do mine on a Hunter machine or equivalent with the help of an expert alignment specialist. It's just so easy and accurate. For me I wouldn't mess with it myself before the upcoming event for fear that i make it worse than better. With that camber you have now you will wear the inside of the Hoosiers down quickly as well although they will last longer than the Kumho's. I always get flamed when I say this but in my opinion Kumho's on ACR-E's as track tires are complete garbage. Borderline dangerous. They work far better on a lighter car with no aero.

I know that Cable goes super quick with lots of camber but for me the tire wear trade off is never worth it. I do this for fun only, not lap records. When you get the chance to get it back to an alignment shop I would run - 2.4 in the front and see how the outside shoulders hold up for you. I would also run dead 0 toe in the front. It turns in plenty fast anyway. It really doesn't need any toe out.

When you can you need to get adjustable end links. Whoever told you they corner balanced your car if it does not have adjustable end links on the sway bars was telling you a story. A car is corner balanced with sway bars disconnected and drivers weight in the drivers seat. Sways bars are then connected and end links adjusted so there is 0 preload on the bars and corner weights remain the same after the bars are attached. Anyone who tells you any different is doing it differently than I have been taught. You can get away with it and on a car like the ACR-E it's still going to work amazingly well but it can be better.

So if it were me this is exactly what I would do. I would measure ride height at the front and I would turn the collars exactly the same amount on both side to get the front to 4". Then I would go to the rear and do the same thing to get it to 5.5". Then I would run it and see what happens keeping an eye on the insides of the front tires. When you have the time I would get it back to the alignment shop and have them readjust everything and take some camber out of it.

Thanks again, that'll be exactly my plan then. The negative camber is the only concern I have left, don't want to murder a set of R7s in less than 2 days. I'm with you on the setup philosophy - I won't be setting any track records, just want to make the tires last a reasonable about of time.
- Do you have any tips for me on how I might go about taking a little camber out myself, if I'm in a pinch at the track and it's burning through the tire too quickly?
I'll be there all weekend so if it is going at too accelerated of a rate, I'll have to figure out something or call it a weekend early. I don't actually know how or where to adjust it on this car, which means it'll only be done as an absolute last resort, but if I have to, do you have any guides you could point me to?
Edit: Nevermind on that, looking through the procedure in the service manual, it seems too complicated to be screwing around with blind like that. I'll just have to live with it until I can get it realigned.

- What pressures cold and hot do you aim for with the R7s?


I'm guessing this 'corner balance' was about as good as it could be done with the factory hardware

rYh42NV.jpg
FV2S6Ab.jpg

[Racingswh]

Hot pressure on an R7 is 32 or so PSI. Disclaimer: This is NOT what Hoosier will tell you to do.

I don't like to see them any higher than 35 in the front. I would start them at 26 and see what happens. I typically start mine at 24 front and 22 rear or 22 all around. If you use Nitrogen it's possible that you will see less inflation during the course of a stint due to less H2O in it. Often times I see tons of condensation coming from the track supplied air pumps and if you do use that to fill tires you may see greater rise in pressure over the course of a session.

Corner weights look fine. I am guessing they left the bars connected but don't know that for sure. Funny seeing how heavy they are right there in black and white. They work so damn well anyway. Just incredible cars.

Pappy touched on it in the other thread and saw the same wear as I did. Inside of the fronts getting torn off. I would run less static camber when you get the chance. He does a nice job of explaining how dynamic negative camber increases out on the track and could very well be why we see the premature wear. I like his suggested static camber settings very much.

Lastly I found that one set of tires was never enough for a full weekend. I go through at least 1 tire per day. Usually a front. That's why I carried at least 3 sets with me. When they start to go away it's great to be able to grab another set and have that grip back again. At the VERY LEAST I would carry 2 more unmounted new fronts with you. That way if there's an issue someone somewhere might be able to mount them up for you and your weekend isn't over prematurely.

For wheels all you're doing is separating yourself from the cash while you use them. As long as you don't damage them beyond repair while you have them that is. I sold all three sets of track wheels in a short period of time and I am sure the new owners will be able to do exactly the same when they are done with them.

[GTS Dean]

The factory alignment recommendations are based on a pro driver under optimal track conditions. Most people will not be able to load the suspension and sustain it that long, so your static camber settings should probably be reduced until you start wearing the outside shoulder. Also, you will probably need less camber on one side than the other based on number of Left vs Right turns and their time of loading for a given track. This will minimize tire wear imbalance.

From the many threads I've followed over the years, it appears that the Kumhos are extremely sensitive to warmup loading. If you hammer them too hard when cool and run extreme negative camber, the inside shoulders heat up and cord very quickly.

[CarbonDan]

Hot pressure on an R7 is 32 or so PSI. Disclaimer: This is NOT what Hoosier will tell you to do.

I don't like to see them any higher than 35 in the front. I would start them at 26 and see what happens. I typically start mine at 24 front and 22 rear or 22 all around. If you use Nitrogen it's possible that you will see less inflation during the course of a stint due to less H2O in it. Often times I see tons of condensation coming from the track supplied air pumps and if you do use that to fill tires you may see greater rise in pressure over the course of a session.

Corner weights look fine. I am guessing they left the bars connected but don't know that for sure. Funny seeing how heavy they are right there in black and white. They work so damn well anyway. Just incredible cars.

Pappy touched on it in the other thread and saw the same wear as I did. Inside of the fronts getting torn off. I would run less static camber when you get the chance. He does a nice job of explaining how dynamic negative camber increases out on the track and could very well be why we see the premature wear. I like his suggested static camber settings very much.

Lastly I found that one set of tires was never enough for a full weekend. I go through at least 1 tire per day. Usually a front. That's why I carried at least 3 sets with me. When they start to go away it's great to be able to grab another set and have that grip back again. At the VERY LEAST I would carry 2 more unmounted new fronts with you. That way if there's an issue someone somewhere might be able to mount them up for you and your weekend isn't over prematurely.

For wheels all you're doing is separating yourself from the cash while you use them. As long as you don't damage them beyond repair while you have them that is. I sold all three sets of track wheels in a short period of time and I am sure the new owners will be able to do exactly the same when they are done with them.

Thanks again for the great info! I'm pretty sure I've watched all your ACR videos on youtube by the way!
I do fortunately have 2 full sets of OEM wheels for exactly the reasons you suggested.
By the end of this summer I hope to make the transition to 18" slick scrubs, but as I'm still in the intermediate stages, I figured it's best I start with the OEM tire, work up to a Hoosier, then go for the real tires. The way your car decelerates from 145+ to 50 MPH is mind blowing. The brakes on this car as-is (girodiscs, ST43, V720s) is already miles above the braking performance of my 2018 GT3.

[Arizona Vipers]

The R7 is going to be a little slower than the Kumho, but will last much much longer. If you want to go fast, A7's all the way!

[Racingswh]

Thanks again for the great info! I'm pretty sure I've watched all your ACR videos on youtube by the way!
I do fortunately have 2 full sets of OEM wheels for exactly the reasons you suggested.
By the end of this summer I hope to make the transition to 18" slick scrubs, but as I'm still in the intermediate stages, I figured it's best I start with the OEM tire, work up to a Hoosier, then go for the real tires. The way your car decelerates from 145+ to 50 MPH is mind blowing. The brakes on this car as-is (girodiscs, ST43, V720s) is already miles above the braking performance of my 2018 GT3.

That's cool. Had a lot of fun in the past 5 seasons running with my friends. So may great times!

You are going to love yours more and more the more seat time you get in it. They are amazing. Faster than almost every other racing car that shows up at an event and that's when it's still bone stock. Well driven they are quite a weapon!!

Funny you say that about decel. One of the first things I came to appreciate and there's WAY MORE left with a Pro at the wheel. It's just about you getting comfortable with waiting far longer than you think you have to to go to the brakes. Just work up to it. Have fun!!

[CarbonDan]

Thanks again for the help!
First track weekend with the Hoosier R7s was a tremendous success!!
Tires are a big upgrade over the V720s. They last a full 20 min session without falling off. Looks like I have tons of tread left after 13 sessions too, and the fresh pavement at the Ridge is very abrasive.
I left my alignment as-is and just adjusted the ride height myself. I think I raised the rear a touch too much as it did have a bit more body roll and a very slight tendency for oversteer. I went 5 turns down on the front and 4 turns up on the rear. I think 3 turns up on the rear should work out better and keep it more neutral, but I'll be having the ride height set properly and re-cornerbalanced soon.
Ran a 1:44.9 at the Ridge without even pushing too hard. I was putting down 1:45s consistently, lap after lap without any fall-off from the tire. This car is a sub-1:40 car at the ridge with the right driver! That'll be my new medium term time goal. I'm taking Turn 1 at about 105 and several instructors told me it could be closer to 130 ideally. I should also be able to take Turn 10 flat out! (Top of the hill on the back half of the track) By the end of the weekend I was running Turn 10 nearly flatout and it's the most unreal feeling in this car where you can really feel the downforce helping you at 125 MPH.

[Racingswh]

Looks and sounds like you had a great time! Video was fun to watch. Thanks for sharing it.

Sounds like you have a plan on how to get quicker there. Will be a fun journey. Great work so far!! Vipers are just such fantastic cars!!

[Arizona Vipers]

Thanks again for the help!
First track weekend with the Hoosier R7s was a tremendous success!!
Tires are a big upgrade over the V720s. They last a full 20 min session without falling off. Looks like I have tons of tread left after 13 sessions too, and the fresh pavement at the Ridge is very abrasive.
I left my alignment as-is and just adjusted the ride height myself. I think I raised the rear a touch too much as it did have a bit more body roll and a very slight tendency for oversteer. I went 5 turns down on the front and 4 turns up on the rear. I think 3 turns up on the rear should work out better and keep it more neutral, but I'll be having the ride height set properly and re-cornerbalanced soon.
Ran a 1:44.9 at the Ridge without even pushing too hard. I was putting down 1:45s consistently, lap after lap without any fall-off from the tire. This car is a sub-1:40 car at the ridge with the right driver! That'll be my new medium term time goal. I'm taking Turn 1 at about 105 and several instructors told me it could be closer to 130 ideally. I should also be able to take Turn 10 flat out! (Top of the hill on the back half of the track) By the end of the weekend I was running Turn 10 nearly flatout and it's the most unreal feeling in this car where you can really feel the downforce helping you at 125 MPH.

Awesome driving dude!!! You should do global time attack there in July. I think you would be in the limited class and you'd do very well. On long weekends like that (13 sessions wow!!) make sure and swap wheels side to side if you don't already.

[blackbeast99]

Thanks again for the help!
First track weekend with the Hoosier R7s was a tremendous success!!
Tires are a big upgrade over the V720s. They last a full 20 min session without falling off. Looks like I have tons of tread left after 13 sessions too, and the fresh pavement at the Ridge is very abrasive.
I left my alignment as-is and just adjusted the ride height myself. I think I raised the rear a touch too much as it did have a bit more body roll and a very slight tendency for oversteer. I went 5 turns down on the front and 4 turns up on the rear. I think 3 turns up on the rear should work out better and keep it more neutral, but I'll be having the ride height set properly and re-cornerbalanced soon.
Ran a 1:44.9 at the Ridge without even pushing too hard. I was putting down 1:45s consistently, lap after lap without any fall-off from the tire. This car is a sub-1:40 car at the ridge with the right driver! That'll be my new medium term time goal. I'm taking Turn 1 at about 105 and several instructors told me it could be closer to 130 ideally. I should also be able to take Turn 10 flat out! (Top of the hill on the back half of the track) By the end of the weekend I was running Turn 10 nearly flatout and it's the most unreal feeling in this car where you can really feel the downforce helping you at 125 MPH.

Awesome! I was going to say the same/ask why you wanted to switch tires - other than the life you will get and the longer sessions. For most events, I'm usually on running 10-15mins which works well for the Kuhmo's and I've only seen about a 1-2sec difference with slicks, so haven't made the jump (but I also usually drive to my events). I'll probably pick up a set of 18's and some stickies soon