When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I am considering changing my wheels/tires to get a larger sidewall dimension in order to reduce the possibility of damaging wheels on Iowas' sucky roads. I am thinking of 18x18 or 18x19 for my GS instead of the 19x20. How close do I need to remain to original diameters front/rear in order to not upset the computers that control ride/handling? I do not really want to go to larger overall diameter, just increase sidewall dimension and maintain same diameter. Hope this explains what I want to achieve. Thanks.
Hopefully some of the track guys that have run the smaller wheels can chime in as to possible issues, but these will be street only tires.
Plug in your factory tire sizes, and it'll give you a list of tire width and aspect ratio that fits AND the % in which it is off the factory rotations by.
For example. If you plug in the front tires for a wide body:
285/30/19
You can see that the closest match to overall diameter size is a 285/35/18 for a 18" wheel. Overall diameter is bigger by 0.8%, or 2/10th of an inch.
Same if you plug in the rear tire sizes for a wide body:
335/25/20
You'll see that in the green zone, if you want to keep the width the same, a 335/30/19 is close but it's 1.1% larger. A 325/30/19 is only 0.4% larger and would keep the front and rear size closes to the original factory sizes. However, most factory ABS/Stability control systems are tuned to account for up to a 3% difference front to back, so the 335/30/19 would work just fine.
When tracking my Z06/Z07 I run 18x11 wheels in the front and 18x13 or 18x12 wheels in the rear. Not sure of the offset but the CCW wheels were originally built for a guy that had a C6 ZR1. The 18 inch wheel will clear the caliper of the ceramic brake cars and mine have enough offset the caliper clears the backside of the spokes by close to a half inch. So 18 inch wheels easily fit over the ceramic brake rotors. The problem you may have is finding any street tire in an 18 inch rim width/tire combination that will give you diameters that are somewhat equal to the stock tread width and diameter.
The guideline to follow is to stay within 4% of the stock Rear/Front Tire Ratio of 1.04. Thus ratios between 1 and 1.08 may work but more than likely 1.03 to 1.05 will definitely work.
Bill
Last edited by Bill Dearborn; 11-20-2018 at 04:53 PM.
So 18 inch wheels easily fit over the ceramic brake rotors.
18" clear the 15.6" rotors on the Z07 carbon brake package? WOW based on pictures I didn't think they would as 18" barely clear the 13.6" rotors with the Z51 calipers.
I guess the 6 piston brakes with multiple small pistons allowing the entire caliper to be slimmer then the base / Z51 4 piston setups. Good to know thanks!
I am considering changing my wheels/tires to get a larger sidewall dimension in order to reduce the possibility of damaging wheels on Iowas' sucky roads. I am thinking of 18x18 or 18x19 for my GS instead of the 19x20. How close do I need to remain to original diameters front/rear in order to not upset the computers that control ride/handling? I do not really want to go to larger overall diameter, just increase sidewall dimension and maintain same diameter. Hope this explains what I want to achieve. Thanks.
Hopefully some of the track guys that have run the smaller wheels can chime in as to possible issues, but these will be street only tires.
I run 255/35r18 and 295/30r19 at the track. No problem at all. That is 1 size smaller diameter than stock. So about 1 inch smaller.
ive also ran 245/35r19 fronts with 285/35r20 rear. That's a 1" taller rear with stock front. No problems whatso ever either. Used like that for 2 years street and track. Apparently the car doesn't care really.
Last edited by BrunoTheMellow; 11-20-2018 at 06:13 PM.
11-20-2018, 10:20 AM
Wheel and tire deviation from stock size
