Has anyone attempted this recently?
What did you run for tires? How did they perform? Did you find an optimal tire pressure?
Would you do it again?
These questions are a perpetual plague on people who prefer stock wheel sizes...I'm not sure if the question has been asked recently or in this way. Any insights are welcome.
Remind me what size tires you're running again?
It really depends on two things- 1- what size rims you have and the tire sizes you're running, and 2- how serious/competitive you're planning on being
With 15" rims it's not so much the sidewall flex that hurts you, it's the lack of available tire sizes and compounds. Sure the taller sidewalls flex more, but that's a pretty minor deal compared to not being able to run a decent compound. There really aren't a lot of options, especially if you're running wider tires. And if you're planning on a single set of tires- as in, you're running the same tires on the street and on the track, well good luck. More than likely you'll either have to run 400 tread wear tires on the track, or track only tires on the street.
If the goal is just to go have some fun autoX'ing, then just run your BFG T/A's or Cooper Cobra's and have a good time. It'll be fun, you'll just slide all over the place and guys with better tires will be faster. On a road track you'll have to be more careful, as the speeds increase the lack of grip can cause bigger issues. But again, if you're just looking to have some fun then carefully figure out what your street tires can handle and have a good time.
Tire pressures depend a lot on the track, the weather, how your car is set up for suspension, how your tire size relates to your rim size, what alignment you've set, etc. What works for one person's car may not be ideal for yours. It's something you have to mess around with. When I was doing trackdays with my motorcycle a lot of days the track provider's staff would give some suggestions on tire pressures, but they were just general guidelines. Some of it is just driver preference too.
I have run 15's autoX'ing, but that was on my '56 Healey 100 and you could get decent tires back then. That car also used a much shorter tire, which is a big deal. If you go down to ~24" tall tires you can still get R888's, Proxes RA1's, Pirelli's, etc for a 15" rim. Can probably thank all the spec Miata guys for that. But go over 25" tall on the tire height and there's basically nothing now.
If you're looking to get serious/competitive, I would suggest getting a set of 17" or 18" Bullits or something similar so you can have a track set up. Nice thing about the Bullits is you can get them as take off's locally for cheap usually.
I'm also interested in this topic as this is something I'm contemplating (I like the look of the old/older school 15" wheels/tires combo), but if autocross is something I'm into I think the answer is large rims and lower profile tires with stiff sidewalls (there is also more sticker tire options with 17/18" wheels). I think the answer may be keep the 15's for the look and swap for larger rims with stickier tires at the track for performance, but I'll await the more experienced member to chime in.
Exactly. Try it out, have some fun, if you decide autoX is something you want to do frequently then I would wager you'll be looking for a set of 17/18" rims in short order. The tire selection at 15" just keeps getting worse. If you run sizes that are generally right for these cars, you're pretty much running BFG T/A's or Cooper Cobra's. Maybe a Nitto if you're running the right size.
IMO it would come down to the tires available in 15 inch sizes. Without an A/B
lap time comparison of 15 vs 17 or larger tires who really knows. I do know smaller
lighter is faster than bigger heavier (wheel tire combo)
Yes, but smaller is not always lighter and bigger is not always heavier. The 275/35/18's on 18x9's that I run are lighter than the 225/60/15's on 15x7's that I took off. For that matter, the 295's in the back were lighter too.
