I've been spending a lot of time looking into the Official Wide Tire Thread. I've found that the primary selection by all these racers is 18" Rims. 9.5 to 10.5" seems to be the most common. RPF-1s w/ +38mm offset is the gold standard.

I've been running stock width stock offset 17" for track wheels for a few years. 245s for normal street tires and 225R17s for BFG R1 and Hoosiers A7. I'm ready to move to a wider section width tire. I do 90% AutoX @ ASP and 10% Track days.

I'd like to stay in ASP, but realize that i'll easily slip into SM. I DO NOT want to cut rear fenders or do anything so dramatic that the car can not go back to stock. I'm ok with a little fender rolling, mild changes that can be done without serious bodywork.

What are the pro/cons of doing a 18x10 versus a 17x10 RPF1? Tire selection? Costs? Sidewall? Overall diameter (2nd gear top speed)?

 

I would normally immediately say yes 18s. But in your case, the 275/35/17 seems perfect for you on a set of 17x10 rpf1s. The wheels are a fair bit cheaper than the 18s and fit up front without spacers though you'll want some for clearance to the strut to max out camber.


The width is a bit narrower than the 285 but that also means less rolling and mods to make clear everything. Its also under 25" like the 285 where the 275 in a 18" wheel is 25.5" and harder to make work.

 

Oh, if you do want to go to an 18, the 255 is very close to the 275 and will fit just as easily. The 255 is kind of a cheater tire and runs much wider than 255 would suggest.

 

Interesting. Just to be clear the sizes you are quoting are for R Comp type tires?

I need to check on tire availability at 275/35R17 from my used r comp source. I feel like his 18" selection is superior.

 

Based on what I've found, availability of 18" tires is far better. Based on what I've read the 275-285 sized tires are a very tight fit with a lot of work needed. For the 255 cheater and maybe up to a 275. Is a 9.5" wide enough? I really don't want squishy sidewalls on track.

 

Go 10". Tires will always like a little wider (not stretched) and if you got to 285s eventually you will be good to go.

 

With the curvature of the OEM trailing arm, an 18" wheel has slightly more inboard clearance than a 17" wheel, so a 17" wheel probably requires a slightly lower offset. The difference is probably only a few millimeters, but it's something to keep in mind when thinking about 17x10s.

Although in ASP and SM you have a lot more freedom in terms of fender modifications or trailing arm replacement, so it's probably not an issue.