PDA

View Full Version : ST(X) tire sizing - width vs OD



cliff96
04-24-2013, 03:13 PM
Inspired by lazyness, and not wanting to change tires at the event - I'm thinking of joining the street tire world.

By my reading of the rules, in STX the max section width allowed for RWD is a 265, and 9" rim width maximum. I'll be a little under prepped without adding an LSD, but with an alignment and DA coil-overs I should be in the ballpark.

The factory spec tire is a 225/45r17 on a 17" * 7.5" (25" diameter) or a 225/50r16 on a 16" * 7.5" (still 25" od)

Last year I ran 888's - 255/40ZR17 on a 17" * 7.5" (25.1" OD) (10.4" O-Width), but will be going with a 17*9 rim this year.


Looking at the R1R's (no 265 - so I can't max out on that) - would I be better with the shorter and slightly narrower 245's or up the OD a touch to gain an extra half inch in width?
245/40ZR17 8.0-8.5-9.5 24.7 9.8 8
255/40ZR17 8.5-9.0-10.0 25.2 10.3 8


Thanks,
Cliff

Daniel
04-24-2013, 03:50 PM
Cliff, I was in your similar situation last year. I ended up deciding on 245/40/17, also on a 9" rim and I'm very pleased with the set-up. I like the benefits of the shorter tire: little less rollover (i.e. more responsive) and slightly shorter gearing. I also think the 245's provide plenty of grip for the power than I'm putting down - I think slightly more than you, though mine may be slightly lighter. The only issue is that you'll be cruising at slightly higher revs on the highway, which isn't an issue for me as it's not my daily driver.

Something to think about

SajBT36
04-24-2013, 04:15 PM
R1R's are pretty squirmy and soft sidewalled too Cliff. Apparently MX5 guys have been gripping harder on the 245's on a 9 than the 255's on a 9 with the tire. Imagine it would go double for the bimmer.

Assuming you have some Toyo discounts/freebies to use? If not (and you're looking to stick with a contingency tire) you might be better on the Yokos.