Grand Sport autocross tire / wheel options?
 

Howdy all,

I've got a tire decision to make for the 2016 season, and I'm open to suggestions.

I'm going to autocross a 2011 grand sport coupe, MT, with those huge 12" wide rear rims and the j56 brakes. 10" wide base corvette rear rims in 18" or 19" diameter don't have enough offset to clear those wide J56 brake calipers (but will clear the OD of the disc).

Option 1: is to run SS (super stock, super street, whatever the new name is) that allows 50 treadwear tires. Hoosier A7s on my factory GS rims become the easy obvious choice. Downside is running against cars/drivers with more power/speed/money than I. And then no significant street driving on them... I'd have to swap back to my steet set of all-season Michellins on base C7 rims and 1" spacers (which I do not feel safe to autocross with), and mean twice the number of lug nuts to tighten (kinda annoying).

Option 2: is to run A Street (minimum 200 tw; no R-comps allowed), and buy Bridgestone RE-11 tires on the stock rims. That model comes in a 325/30/R19 that makes full use of that 12" wide rear rim. Pluses are lower cost, and using all the rims to maybe make-up for the car being VERY wide. Minus is the RE11 is not as competitive as the newer Rival-S and RE71R - which all the non-GS cars will be on.

Option 3: is to run A Street, and find a set of 18" diameter 12" wide rear rims that have the right offset to clear the brakes. I'd run Rival-S 335/30/R18 tires on the rear, maximizing the tire "contact patch" that I can get by the rules. I've not yet found a wheel/rim that fits this situation?? If any wheel sellers out there can guarantee correct fitment for a competition-strength wheel, I'm a customer. I'd need matching front rims in 17" to fit the smaller OD 245/45/r17 front to keep the ABS/ESP happy.

Option 4: is to run A street, and find an 19" dia, 10" wide or 11" wide rims to fit the narrower 285/35/r19 RE71r rear tires & stock size fronts. This again requires a rear rim size that I've not successfully found - it needs the right offset to clear the J56 caliper. If anyone can recommend/guarantee the right rim, I'm a customer. I'd be on a competitive-spec rubber compound...but would give up 1" to 2" of rubber width - which would not take advantage of all the "tire contact patch" I could get.

Any recommendations/suggestions?

It must be autocross tire quandry day - I just saw activity in c4cruiser's older post that is a different situation. The corvette central rim spec link is just what I needed.

I perceive for my option 3 I'm looking for 18" x 12"wide, +59 offset rears & 17" x 9.5" or 10", +40 offset fronts.

And for my option 4, I'd need a 19" x 10" or 11" wide, +59 offset rear.

I'm an option 1 kind of guy.. When I had my GS, I went 18" ccw's all the way around around with A6's at the time... I also had headers so I was a SSP car, and was not worried about other cars/drivers and the GS can handle its own if you can make it do what you want....

But it did have me resort to trailering the car to events so i didn't have to do the parking lot change...

Get in touch with Sam @ stranoparts.com. Problem solved. :thumbs:

I've read the first post a couple times and I'm kind of confused, but the basic jist of my post is to say that if you're looking to run A-Street, you can't change wheel widths, only diameter. Also I'm not following the logic of downsizing the fronts to 17's, when the biggest 17 you can get in the hot tires is 255.

The easy choice is option 1, run SSR on A7's on stock wheels. I'm not following you on more powerful/more speed/more money, C6 Grand Sports more than hold their own in SSR.

For A-street you're looking for 18x12" rears to run Rival S's 335/18 rear and an appropriate front tire on the stock 18x9.5" wheels. I think the fast C6 Z/GS drivers in A-street at Nationals crammed 315/18 Rival S on the front.

All the Rival-S 18" rim diameter options are within 1/2" of each other on OD of the rubber.

The abs/esp is looking for that around 1" difference on the rubber OD, and is apparently very unhappy if it doesn't see it.

The Rival 335/30r18 OD is 25.9", and the 255/40/r17 OD is 25"..so hopefully those 2 satisfy the abs/esp computer. But, this OPTION 3 choice requires me to buy 4 new rims....sigh...

Anyone autocrossing on the the Bridgestone RE11 anymore? Or if you did use them a few years ago...were they decent, at least OK...or total crap?

Running in SSR means I gotta fight it out with 505hp z06s & +600hp zr1s on tires that can actually handle all the power. In AS, only 200tw tires are allowed...so it's more difficult to actually use ALL THE POWERZ.

Of your options originally posted, option 4 will be competitive, but will cost $$ for wheels. Option 2 is good but instead of the uncompetitive RE-11, use a 285/30/18 RE-71R on the front (comes out in 2 weeks) and use a 305/30/19 Kumho V720 in back until August. Then when Bstone brings out the 305/30/19 Re-71R in August, you hit that.

Tell that to the guy who won Nationals in a c5z, or the guy who finished 4th in the GS.

SSR or A-Street on 18" all around are the best choices. RE-11's are not competitive. And no, you don't want to wedge 315's on the 9.5".

The GS in SSR is very competitive. As mentioned one was 4th @ nationals. I had one and won a lot of events in it. I just prefer the Z06 as a car overall. The C5 is still best all around autocross Corvette IMHO.

What size did they (the top C6Z/GS AS guys) use? I thought I read that some used the 315 Rival S on the front.

275's. Some were running 315's when the first run of 275's were scrapped and they were vaporware. I opted for 275 having seen the 315 Rival S on a 9.5, and having driven the 275's on a 9.5. This is for those, on Hoosier's, I'm still on 315's.

Thanks for Posting Question
 

Thanks for posting this question. I just got an 11 GS and am planning to run a few local autocross events this year. You came up with more options than I did. It would be much easier decision if the RivalS or RE71R came in stock sizes for the GS.

I also want to thank those who responded. Great information.

I did wonder if running 18" F&R what size combo you use to maintain the F/R recommended 1" stagger or do you just turn off traction aides or is the stagger requirement overstated?

Thanks

I have to take some time to read this, I think we might be overthinking this... I'll be back.

If your not looking to win the class then there is no reason not to run the re-11's in AS. The upside is they are good in the dry and rain for the street.

That is a very good suggestion.

There are 2 small issues. First, my son and I share a 97 Miata and we ran the RE-11 a couple of years ago and I thought it was fine. Then last year we ran the RE71 and I could not believe how much better it was. Second, even when I say I'm just running to have fun, of course I want to win my class. Realistically, I'm not good enough to win most of the time, and it is still lots of fun. My son is now consistently faster than I am.

So I will probably stay up way too late a few more nights searching the forums and analyzing the options and then likely get the RE11.

I ended up going with stock sizes, re71r front and re11 in the rear. At the starting line, I try to just do a nice hairy burnout to heat up the rears so they stick.

With 1 event on this setup..the first run did feel loose in the rear, but the following 5 felt a lot better.

I'm trying for 8k to 10k miles this season on the car, with 1-2 commutes to work per week and some pleasure driving...hence the non-nationally competitive setup. I'm a casual autocrosser, not a raving hardcore nationals guy.

19" rear tires
 

I have a 2011 GS with 2 sets of stock 18/19" wheels. Has anyone tried the 305/30-19 RE-71r in the rear yet? Seems like it might be a bit small for the 12" wide wheel. I'd go with the Rival in the rear, but I don't have any 18" rear wheels. Just looking for the best option for a rear tire for SCCA AS use on a C6 Grand Sport.

The best options is likely the Rival S in 335... but it is an 18" and clearly requires you buy wheels. If you don't do that, then you on an undersized tire (by quite a lot in fact) on a car that really likes rear tire.

If you run a Rival S 335/30/18 in the rear, what size do you run in the front?
Based on Tire Rack data the Rival S 335/30/18 is 25.9" diameter and the 275/35/18 is 25.6" diameter. Based on information from other threads in this forum, the traction control and ABS systems want a ratio rear/front of 1.04 but will tolerate a range of 1.04 - 1.06. I don't know if this is correct, but it is what I read.
I would be happy to buy appropriate wheels to run the tire sizes listed above if it doesn't cause issues with the ABS or Traction Control or if there is some additional action that can eliminate issues.
Thanks

I've run a couple of events in my GS with no Traction/Active Handling issues. 335/30/18 in the rear and 315/30/18 in the front.