COM Sports Car Club

what i have found with poeple that tend to go with over sized tires for road racing any way is that they don't come up to temp .
this is what we found with the V8 miatas with some test days at the tracks .
with the 10" front tires they could just not build the heat into them they need to bite .
at best we cound only get them up to 160 degrees when they need to be in the 190 degree range to stick .
we did get that tenp when we went to the 9" wide front wheels .
more of a foot print on the ground is not better if you can't build the heat in the tires they need to bite and stick to the track .
we were getting the heat into the rears with the 10's but again it was with a V8 powered miata so there is more power to help build the heat there .
also the V8 adds more nose weight so running a bigger tire is kind of a must as not to over heat a 7 or 8 inch wide tire .
an auto cross tire is designed to work a lower temps so that maybe why they can get away with using a 10" tire ?
way back in the day when i would do autocrossing i would not ever use a 15" wheel i would use a 14" as the rolling radius is smaller and you get better execleration from the 14 than the 15's .

I believe that these are all valid points for a road race car. Autocross, however, is a very different animal. Starting with the fact that we run Hoosier A6s, which are designed to heat up very quickly. So quickly, in fact, that on a good 80+ degree day they need to be sprayed between the runs or else they get very greasy. And we are talking 60-70 seconds per run here. More to the point, I've been running 255/40-13 (sic, 255s on 13x8.5 wheels) for at least the last 4-5 years, probably longer. For the exact reason you've mentioned - to get a little better acceleration. And the fact that wheel/tire combo clocked at 24 lbs was great too. Unfortunately, there are no wide tires in 14th. The next step is 275/15 and that's what all the faster people went to as soon as this size A6s became available. They've been tried to 8", 9" and 10" wheels and have been found consistently fastest on 15x10. They also don't wear out nearly as fast as they do on 15x10s.

In either event, Scott at FastTrack has been cutting and beating on the car for the last two days (I want to extend my public and very heartfelt THANK YOU! to Scott and FastTrack for being... well, being good people and a good business). We'll see what happens at the event this Sunday, whether there's any serious rubbing.

paultg wrote:Are you setting the car up for autox or track? Is it stock power?
Be cool to see it with 15x10s.

I only run 15x7 with a 205 at track on the NA. Until I'm running spec Miata or better lap times I don't see a need for more tire.

Paul, this a purely and autocross car. If you want to see it, I should be at Fort Devens on Sunday. Swing by, it'll be interesting

the setup are totaly different as the type of racing is different .
back in the day when i used to race in autocrosses we did not want tire temps any thing over 140 degrees were we would shoot for the 125 degrees range . the tire temps you want to get there as soon as you could as the runs for the most part are very very short .
we in no way would try and cool the tires as we would try and keep them at there run temps of 125 or so because the run were so short .
we would also add in some more negitive caster to quicken the steering and change the tow .

Well, as a little feedback, the car ran today without any rubbing that I can see or feel. Rears were pulled and hammered, not cut.

Again, my hearty thanks to Scott at FastTrack for getting this done and getting it done right before the weekend autocross. Great job and great pleasure. Hope you had a good race weekend, Scott!