986

Has anyone mounted 285/30R18 (R6 or BFG R1) on 9" rims?

Both companies say their 275/25 fits 9" rims, but their 285/30 are for 10-11" widths.

Thanks!

mdrums

I've always been told and practiced...it's always best to mount tires on the widest rim possible. This keeps sidewall movement in check on turn in. When wide tires are mounted on narrow rims the sidewall movement side to side increases.
I was reading in Grassroots magazine a couple of years ago about some guys doing what you are trying to do and they found they actually had faster lap times on the slightly narrower tire on a max width rims than by just going to a wider tire.

986

Thanks. All else is not equal though... Class Rule dictates how wide a rim can be used, and 285/30 has better gearing than 275/35 (unless I go down to BFG 265/35). Hence the question.

Thanks!

Paddy

Toby, I've always used a 265/35 on the 18X9 wheel.

utkinpol

i saw some scca boxsters with 285 A6 tires on 9" rims but those were AX cars, i have no idea of what advantage it may/will give on a track where dynamics are a bit different.

ps. they were most likely 9.5" rims so I am probably wrong.

flatsics

You should look at the Hoosier 255/35/18. They are a 245/35/18 with a one inch splice added to the tire. They really measure out as a 270/35/18 and they are shorter than a 285/30/18. They were designed for cars that are required to use 9" wheels by SCCA.

986

Thanks. This is very helpful.


I think you are actually right. SCCA "AX Stock" 986 Boxster S' run with 9" rear wheels. Thanks!

mark kibort

9s or 9.5s fit 275s best. Ive run up to a 285 on a 9.5" once and it was a decent, but tight fit.
I currently run a 305 on a 10" rim, which is this kind of fit. sure, 10.5 or 11 would be better, but it is safe and works.
I wouldnt worry about the difference in terms of gearing. that can work for or against you as far as an optimal change. gearing doesnt give hp, it only optimizes the hp you have for a specific track or speed range.

bobt993

Check with CCW. They are pretty firm about why this does not work very well. I am running 10's up front with 275s and 12s in the rear with 315s. Tire combo works extremely well.

Gary R.

I would do what Doug says...

Ile

Hey 986 -

I know this thread has been long dead but I figured I would ask - Did you ever go through with this? If so, how did you like the setup? If not, what did you go with?