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Bare with me here, I'm working on my new autox Track Day build. I come from 5 years of racing a miata in STR. I'm building my 02 SS for STP. so 200tw is requred
I plan on using a square setup 18x10.5 wheels. I'm debating between 285 or 295 wide tire to wrap them in, specifically the Hankook R-S4.
On the miata, it was best to run a 225 on a 15x9 wheel, that way there was a little bit of a stretch to the sidewall. Is a little stretch still good for the heavy Fbody? Or should I try and oversize the tire to the wheel and have a pinch?
Hell, I could cram a 315 Rival-s on this wheel and get one hell of a pinch. Should I?
Pinching the street tires doesn't really pay off. It can work on Hoosiers but I wouldn't put a street tire bigger than a 305 on them. Doesn't seem to be much info on the RS4 yet. I wold also consider the newest BFG Rival and the Nexen SUR4G.
Thank you for the input.
I would agree, my experience says pinching a street tire is not good. But I had to ask bc I see countless fbody that stuff huge street tires on "track day cars".
18X 10.5 square with 315/30/18 BRG Rival S (200tw)
i came from a square 285 RS3s setup on my camaro (18x 9.5)
and in comparison these are AWESOME
wheels and tires.
Square setup 4x
18 x 10.5
315/30/18 Rival S
unfortunatly they wouldnt clear my calipers. bought some 1/4" spacers first but those were only enough for the rear. the front needed 12mm spacers. Both hub centric. also picked up some extended shank lugs to grab more threads lost from the spacers.
A Rival S is going to be much better than the RS3 out of the box even without going wider, not really a good comparison. Especially on a stick axle car you are just going to eat that outside shoulder.
Going from 18x10.5 and 315 Hoosiers to 17x11 and 315s was a significant upgrade. Street tires would benefit even more from the extra wheel.
Another you might consider is Yokohama AD08R in a 295/30-18. That is what I used for a week long event. Different track every day with commutes. Seemed to not fall off over 15-20 heats minutes on track. A video of them.
I've walked around the paddock at several competitions at Road America, Gingerman, etc, and most of the production based cars I saw ran 275-wide square setups at the largest. Some exceptions obviously (vette, viper, etc), but I wonder if 275 is good enough for these gonzo fast competition cars, is there really a benefit to going wider?
I've walked around the paddock at several competitions at Road America, Gingerman, etc, and most of the production based cars I saw ran 275-wide square setups at the largest. Some exceptions obviously (vette, viper, etc), but I wonder if 275 is good enough for these gonzo fast competition cars, is there really a benefit to going wider?
Are those cars actually built to go fast or look good? Every serious autocross-er I know that runs a heavy, higher HP car puts the biggest tire in the best compound on the biggest wheel they can get on the car. Sometimes a smaller tire in a better compound will be faster than a bigger tire in a slow compound, but given the same compound and the proper wheel to support it, wider is better in my opinion (at least for autocross).
The only way to know for sure is to test, but when I see Miatas that weigh 2300 lbs running around on 245's, I don't see how an f-body could be fastest on only a 275. C6 Z06's in A Street that are winning are running 335's out back.
Road course tire requirements are different than autocross tire requirements. DSP BMWs that make 250whp and weigh under 3000lbs are significantly quicker on 315s instead of 295s. Don't see an Fbody hitting that upper limit until ~335 Hoosier territory.
How temperature sensitive are the Rival S? My R888's drive completely different between my first and last runs which makes it hard to be consistent.
Originally Posted by 1981TA
I've walked around the paddock at several competitions at Road America, Gingerman, etc, and most of the production based cars I saw ran 275-wide square setups at the largest. Some exceptions obviously (vette, viper, etc), but I wonder if 275 is good enough for these gonzo fast competition cars, is there really a benefit to going wider?
My understanding was for autocross and other "lower speed" events the more rubber you can fit the better. But for higher speed road courses the added weight of a bigger tire can negate the benefits of additional mechanical grip. Would love to see a comparison using the same compounds.
Good discussion and all good stuff to know or consider.
FWIW: For the longest time, I ran a 245 square setup until a brake upgrade forced me into larger wheels. 17x9.5's were a pretty common upgrade path, but tire selection for that size is getting a little slim. I bumped up to 18x9/Hoosier R comps this year for road race, and C5 (17x8.5, 18x9.5)/Bridgestone RE71Rs for street/autox. The car is way more capable than I am at this point :-)
How temperature sensitive are the Rival S? My R888's drive completely different between my first and last runs which makes it hard to be consistent.
My understanding was for autocross and other "lower speed" events the more rubber you can fit the better. But for higher speed road courses the added weight of a bigger tire can negate the benefits of additional mechanical grip. Would love to see a comparison using the same compounds.
I can't speak to the Rival comment but I have also heard the same thing about running big meats at road racing. Autocross seems to be "stuff the biggest tire you can" while road racing you need to be more conservative and smart about it...and that's not even getting into autox/road racing compounds. Tire warmers and or a tire that heats up faster would help you.
Originally Posted by 1981TA
Good discussion and all good stuff to know or consider.
FWIW: For the longest time, I ran a 245 square setup until a brake upgrade forced me into larger wheels. 17x9.5's were a pretty common upgrade path, but tire selection for that size is getting a little slim. I bumped up to 18x9/Hoosier R comps this year for road race, and C5 (17x8.5, 18x9.5)/Bridgestone RE71Rs for street/autox. The car is way more capable than I am at this point :-)
Interesting you are running a diameter and width difference front to back.
Interesting you are running a diameter and width difference front to back.
I scored some stock c5 wheels cheap, and these were the sizes they came in. I figured it was worth a shot to play with them while I await delivery of custom forged 18s. I've never really had traction issues in front. They've always been in back, due to trail braking or trying to over power corners.
04-27-2017, 11:07 AM
autox / Track Day tire for 18x10.5 = 285 or 295 
