Ok this is just a FYI to help anyone who might be changing tire size, I happy with my results and can’t wait to autocross this car . Ok (I) wanted R71R’s on ( my) car and the biggest I felt would be safe on factory wheel was a 275/35/19 up front on the 8.5 wheel needed to stay in SS class ,the concern was the biggest 20 inch is 295/30/20’s for the rear which are only .4 inches taller and with my front wheels pinched I feel they are pinched a little taller than normal? I could have went with the 285/35/20 rears but going to a 295 from a 305 was hurting me enough , ok let me get to the point of post , not every key cycle but every now and then when i first start car and start driving the T/C light on the dash flash’s and the brakes apply themselves this actually happened with my c7 zo6 when I went 18’s front and back and the fix is the same as c7 - all I need to do is push the T/C button off for a few seconds while driving and when I put the T/C back on ( push button) the car is fine and doesn’t happen again on that key cycle. Ok that it I’m posting to help people that’s all , maybe the R71R’s will come in taller/ wider sizes in the future? But until then this is my fix , actually any type of tracking/ autocross I will be doing I will double click anyway. Thanks for reading and personally I think square will work on this car .

 

I’m going with an 18”/19” set-up for SS. Haven’t decided on RE-71Rs or Rival S 1.5 yet.

 

the 18/19 was initial plan but I wanted exactly the factory offsets without spending 5k per set for one piece wheels , I stole this 2nd set of factory wheels ( cheap) , what is your plan for wheels and cost? With the 18/19’s your after you can go with 275/35/18 front and 305/30/19 rears with the R71R’s and definitely won’t have issues.

 

Good to know, thanks for sharing.

 

There are a few manufacturers out there making fully forged custom-sized wheels for way under $5k/set. More like ~$3k, depending on finish choices and options.
I went 18/19 on my car, though not stock widths. WIth factory widths I probably would have stayed in the 245-255 range, beyond that things are getting really pinched.
I have 275/35-18 front but the wheel is 10.5" wide... just about right for that wheel width.
Going 19 in the rear allows you to use the 305 RE71R if you like that tire. I'm using the GY Supercar 3's, which might be OK at a ProSolo or warm event with 2 drivers, as they need some heat in 'em.

In general, a square setup is one where the front and rear tire widths are the same. All of your complications have to do with the car's unhappiness at the change in circumference ratio from front to rear. Certainly given the range of choices available, there probably existed a square tire combination that wouldn't upset the TC but given the rear wheels are 2.5" wider than front, it would have been a mess to try.

 

Any word on when the larger sizes RT660s are coming out? Could run 255/35r18 and 315/30r19 on stock width -1” rims while still keeping the stock ratio front to rear.

 

your right I shouldn’t have used the word square when I actually was talking about tire heights, thanks

 

I have a set of 18"/19" with OEM width on its way, and a non-OEM offset to take advantage of the rulebook allowances for SS. I will probably put RE-71Rs on them as one of my buds is getting a C8 as well and he has Rival S 1.5 ready to go, so we can do some comparisons. As I don't have the wheels yet, I don't want to mention the maufacturer but I will post up some pictures and description when I get them. Plus I need my car! I am also thinking of a second set of wheels, OEM diameter and width, custom offset, for street driving and rain tires. Will be a different vendor.

As jrhoades mentions, there are companies out there that will are in the $2.5k to $3.5k range . . . MRR and BC Forged both have attractive offerings.

 

Al... I didn't know you were getting a C8 - Very cool! I look forward on hearing what you and Jason are liking/disliking about the car around the cones. I doubt ours will ever see cone action..lol

 

Yeah, I've been keeping quiet about it until I actually take possession. It was supposed to be built week of March 23rd, but Bowling Green closed the week before. I am looking forward to sorting through this car and seeing how good it is as an autox car.

 

Awesome. I know nothing...lol

Looking forward to hearing about it as well. Next time I autocross my own, it will be a C7 GS, but that's at least 2 years out.

 

One thing that we have to remember is the issues with TC, stability control etc if you are to far off the factory dia front to rear.
when you say it protest and you can make it go away, you might turn light off but your stability track program , TC etc. will struggle on track ?

Rule of thumb on C6 and C7 was not to exceed 5%, and the further away from that 5% difference the less chance of overworking and getting a car that fights the forces during a track event...
I always tried to find tire combo that put me less than 2%.

Not sure if that's still the case, but something to keep in mind ?

just my 0.2c