Class rules require DOT street legal, max size 225/40R18. If there was a benefit to it I could fit something smaller, as it was an option available. Anybody want to chime in with a recommendation? Currently running on my Kumho Ecsta LE's. they're my daily driver tires, and the wear is worrisome.
You sure you need to run stock size? If you are in one of the street tire stock class, you are limited to stock size wheel(diameter and width), but you can run any size tire you can fit on that wheel....
Great Point! I do not really know enough about tire dynamics to understand whether I want taller sidewalls or shorter, wider contact patch or narrower. Can you just give me a quick sentence or two on how these variables interact?
I DD the same set of wheels and tires that I track/autoX, so I sized mine with the stock rolling diameter in mind and came to a 245/40/17, which is actually smaller rolling diameter compare to stock. If I can actually get 255/40/17 for the tires I want I'd probably get that since its the exact stock diameter. My goal is to basically not have issue with rubbing and stuff.
There is a guy on the MK6 forum that managed to fit a set of 285 Hoosiers(IIRC) on the stock 7.5" Detroit/Huff wheel, so I'd imagine thats pretty close to what the limit is.
As far as diameter goes, smaller diameter gives you an effective shorter gearing, should help with acceleration, for something like autoX where your speed is low, its mostly desirable. For me though I am just going with closest to stock as I can. Sidewall height will affect steering response to some degree, more sidewall general equates to sloppier response, as rubber tend to give more where there is more of it. But in this case we are looking for ultimately more rubber to the ground. Running the same tire pressure between wider and narrower tire gives you the same contact patch size, but wider tire at this point is stiffer wheel rate wise, so if you keep the same wheel rate, you can run lower pressure, which gives you bigger contact patch size. The biggest difference I see running wider tire also is the tire pressure, the pressure change before and after a run is much less varied on the wider tire, which should mean more consistent handling.
So if I understand you correctly, the wider contact patch, coupled with a stiffer sidewalk, is the point. If you do not mind my asking, what about 235/30 R18 or a 235/25 R18? Can we get the same effect with out stretching the tires? Narrower sidewall and wider contact patch, right?
You probably could, but for practical reason you probably don't want to. Sidewall will help with dealing with with bumps, not bang up your wheels...etc. The extra "give" in the sidewall also should give you more predictable transition between gripping and slipping. If you do want to run smaller tires, you probably want to go to the smallest wheel size that fits, but that will take you out of "stock"...