Wider Front Tire Only?
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Intermediate
Joined: Aug 2016
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Wider Front Tire Only?
So I sold my C6 Grand Sport and recently picked up a C7 Stingray, which I absolutely love (although I'm still trying to get over the look of not having 345's in the rear). The car came with basically a brand new set of Mickey Thompson's in the stock 245/285 sizes which I planned on keeping, but here's my dilemma.
The wheels I'd like to buy for the car are 18x9.5 and 19x10, and I'm thinking a 245 on a 9.5'' wheel will look too "stretched". Does anyone know if I can do a 255/40 or 265/35 front tire while keeping the 285/35 rear and still have the Traction Control system be happy? If I remember correctly the C7's like to have a 1.2 diameter difference but how far (higher or lower) can you actually stray from that before you have issues? I've read through a lot threads on this but haven't found one where someone kept the stock rear tire size.
The wheels I'd like to buy for the car are 18x9.5 and 19x10, and I'm thinking a 245 on a 9.5'' wheel will look too "stretched". Does anyone know if I can do a 255/40 or 265/35 front tire while keeping the 285/35 rear and still have the Traction Control system be happy? If I remember correctly the C7's like to have a 1.2 diameter difference but how far (higher or lower) can you actually stray from that before you have issues? I've read through a lot threads on this but haven't found one where someone kept the stock rear tire size.
Le Mans Master
Joined: Aug 2000
Posts: 5,529
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From: Austin Texas
Ideal
Spec Diameter Width
235/40ZR18 21.7008 8.8563
245/40ZR18 21.8583 9.2500
265/35ZR18 21.6516 10.0374
275/35ZR18 21.7894 10.4311
285/35ZR18 21.9272 10.8248
275/35ZR18 is a slightly better fit in diameter than 285/35ZR18
However, you want to keep the width ratios similar to avoid inducing oversteer or understeer. In order to match the 275/35ZR18 you will want::
x = originalrear/originalfront*newfront
x = 285/245*275
x = 319
Spec Diameter Width
235/40ZR18 21.7008 8.8563
245/40ZR18 21.8583 9.2500
265/35ZR18 21.6516 10.0374
275/35ZR18 21.7894 10.4311
285/35ZR18 21.9272 10.8248
275/35ZR18 is a slightly better fit in diameter than 285/35ZR18
However, you want to keep the width ratios similar to avoid inducing oversteer or understeer. In order to match the 275/35ZR18 you will want::
x = originalrear/originalfront*newfront
x = 285/245*275
x = 319
Le Mans Master
Joined: Oct 2011
Posts: 7,079
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From: DFW, Tejas!
The car already understeers a bit. You can go wider in the front and not turn it into an old school 911.
I went 315/335 and its almost perfect. When I start to lose it, it went into a 4 wheel slide.
I went 315/335 and its almost perfect. When I start to lose it, it went into a 4 wheel slide.
Racer
Joined: Jul 2013
Posts: 276
Likes: 21
From: Morgan Hill CA
Does the car not calibrate if you have different ratio? I'm looking into different autox tires now. When I had C6 Z51, right after I mounted the different tires, the car auto calibrated. Is this not the case for C7?
Le Mans Master
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From: DFW, Tejas!
Advanced
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From: Mckinleyville Ca
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Le Mans Master
Joined: Oct 2011
Posts: 7,079
Likes: 1,922
From: DFW, Tejas!
11 x18 inch (track setup)
On either my first or second session and I got a turn mixed up. I thought it was a longer turn and suddenly switched back left. You can see the car just does a perfect 4 wheel drift. I was seriously surprised- I expected a spin for sure. 315F 335R was perfect- any time I got loose, it was all 4 tires. I'll try to find the video again
On a narrow body car, I'd probably try to run a about the same type setup, almost square but slightly wider in the rear. A stock LT1 really doesn't really even 335 rear when it's an R-compound. It can put all the power down.
edit: correct video
Last edited by village idiot; Dec 21, 2017 at 10:34 AM.
Tech Contributor
Joined: Jan 2015
Posts: 5,688
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11 x18 inch (track setup)
On either my first or second session and I got a turn mixed up. I thought it was a longer turn and suddenly switched back left. You can see the car just does a perfect 4 wheel drift. I was seriously surprised- I expected a spin for sure. 315F 335R was perfect- any time I got loose, it was all 4 tires. I'll try to find the video again
On a narrow body car, I'd probably try to run a about the same type setup, almost square but slightly wider in the rear. A stock LT1 really doesn't really even 335 rear when it's an R-compound. It can put all the power down.
edit: correct video
https://youtu.be/ymvN3d5Dj04
On either my first or second session and I got a turn mixed up. I thought it was a longer turn and suddenly switched back left. You can see the car just does a perfect 4 wheel drift. I was seriously surprised- I expected a spin for sure. 315F 335R was perfect- any time I got loose, it was all 4 tires. I'll try to find the video again
On a narrow body car, I'd probably try to run a about the same type setup, almost square but slightly wider in the rear. A stock LT1 really doesn't really even 335 rear when it's an R-compound. It can put all the power down.
edit: correct video
https://youtu.be/ymvN3d5Dj04
but you already knew about that hahah.
Last edited by BrunoTheMellow; Dec 21, 2017 at 12:09 PM.
Tech Contributor
Joined: Jan 2015
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I an currently running a 1" taller tire in the rear and stock height tires in the front. The car didn't do anything different so they are pretty lenient. Have been for over a year with plenty of track days. Although I must warn you, rubbing sucks, taller ratios suck (z51 already struggles due to the big gap from 3rd to 4th). Everything in PTM works.
Last edited by BrunoTheMellow; Dec 21, 2017 at 12:14 PM.
Le Mans Master
Joined: Oct 2011
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From: DFW, Tejas!
275-295 probably for z51. Although it really depends on your alignment and suspension setup. I've had a perfectly balanced 4 wheel slide car , a pushing car, and an oversteering car with the exact same tires 245/285 , just different suspension stiffness settings, tire pressure and alignment settings. I must say that having 1° more negative camber up definitely made the car oversteer but now it never pushes which is surprising for such narrow front tires.
but you already knew about that hahah.
but you already knew about that hahah.
Drifting
Joined: Jan 2005
Posts: 1,441
Likes: 557
I have similar results to Village. Exiting the sweeper at Buttonwillow on the stock tires, was causing massive understeer. I’m now on 315/345 and I do nice planted 4 wheel drifts. But, I have also gone .05 toe out front and rear with maxed camber. I’m at -2.8 front and -1.8 Rear. It seems like GM build in understeer for safety using a smaller front tire. I prefer the car oversteering with controllable characteristics.
Racer
Joined: Jul 2013
Posts: 276
Likes: 21
From: Morgan Hill CA
I have similar results to Village. Exiting the sweeper at Buttonwillow on the stock tires, was causing massive understeer. I’m now on 315/345 and I do nice planted 4 wheel drifts. But, I have also gone .05 toe out front and rear with maxed camber. I’m at -2.8 front and -1.8 Rear. It seems like GM build in understeer for safety using a smaller front tire. I prefer the car oversteering with controllable characteristics.
Le Mans Master
Joined: Oct 2011
Posts: 7,079
Likes: 1,922
From: DFW, Tejas!
I'm running 315/30/18 in the front on 18x11 wheels. I'm sure if you PM the guys who do the signature wheels on this forum, they can give you the offsets they use. I didn't notice any rubbing at all.
We don't have many options for running a track tire that wide though
Hoosier R7/A7 (about $1600/set)
Ecsta V720 ACR - if you get 19's all around (315F, 355 R) ($1300)
Cup2 tires in a bunch of sizes ($1900)
R888R in a few different sizes ($1100-1300)
Those goodyears on the ZL1 1LE (305/325)
And some pirellis. That's about it.
Drifting
Joined: Jan 2005
Posts: 1,441
Likes: 557
Amazingly I’m not rubbing. I had some issues with traction control and slicks, but no issues with traction control turned completely off. I mistakenly though “RACE” mode was all off. It is not. I was having TC kick in durning triple digit corners on slicks, as the car though I had reached an impossible G threshold. Otherwise, zero rubbing. I’m running CCW TS12 18”X11” fronts with 18”X13”’rears. Running Hoosier R7 315/345 combos. Cool part is the slicks are only a few tenths off the stock front to rear ratio. I’m going to try A7’s next. I absolutely love this set up! Full steering lock barley touches and has not left a mark yet. During TC engaugment, my tire would barely touch the inside fender liner and fender lip while under full compression and having the brake activated, moving the rear tire back on forth under load. Even that, did not burn through the liner!
Edit: I have a Grandsport with widebody. I think some guys on this forum have fit some pretty wide rubber under the Z51. Can’t remember the details though.
Edit: I have a Grandsport with widebody. I think some guys on this forum have fit some pretty wide rubber under the Z51. Can’t remember the details though.
Last edited by rb185afm; Dec 22, 2017 at 03:20 PM.
Racer
Joined: Jul 2013
Posts: 276
Likes: 21
From: Morgan Hill CA
Good to know you guys are not rubbing with 315/345.
I'm running in a street tire class so it limits my selection even more.
Last edited by Takoyaki; Dec 23, 2017 at 12:10 PM.
Tech Contributor
Joined: Jan 2015
Posts: 5,688
Likes: 1,450
Hope I'm not going off topic. The stock front to rear tire height ratio is the rear tires being slightly taller than the front. I have Z07. Is this the ratio I need to keep in order not to confuse the traction control?
Good to know you guys are not rubbing with 315/345.
I'm running in a street tire class so it limits my selection even more.
Good to know you guys are not rubbing with 315/345.
I'm running in a street tire class so it limits my selection even more.