BlueJay73

Have 2011 997 C2S.
9x18, 12x18 wheels
Open lapping, DE's.
Tire manufacturer websites (Toyo, Yoko, Nitto, etc) all say 295's, 305's, 315's all should be installed on a 11 or11.5 inch rim max. None of them recommend putting these tires on a 12 inch rim.
What do you knowledgeable track gurus do? Is it safe to stretch these tires on a 12 inch rim?
Many thanks for advice.

utkinpol

I run 275 nt01 in front and 335 ra1 on those rims.
You definitely can run any 245/305 combo on those rims. Toyo R888 makes 305 that fits fine on 12" rim.
Pretty much any tire that says max rim size 11.5 will go fine on 12" rim. Do not worry.
Only parameter you need to keep an eye for is to have rear tires diameter bigger than fronts. Otherwise some say psm/abs may give a cel, but it is unproven.
If you can - test if 245 / 315 NT01 nittos work fine on this car. 315 is slightly smaller than 245 and no one knows if it works OK or not.

seapar

I was told by Damon of tire rack that 245 40 18 F and 305 35 18 R will work on those rims. Pretty much toyo R888, though.
check that the OD are pretty close. A 335 30 18 may work or may be a bit tight depending on fitment.

Lugs H

'06 C2S... Track wheels are 9x18 with 245/35x18 & 12x18 with 315/30x18 Hoosier R6 tires.

mdrums

on 9x18 and 12x18 these 2 fitments work with out any fender or tricky suspension mods:

245/40/18 front
305/35/18 rear

or

255/35/18 front
315/30/18 rear

I ran these fitments on same sized wheels using Toyo RA1 then R888...no issues fitting at all.