245/40 vs 255/40 on 9" rim

[Yvrbmw]

Has anyone run both for comparison? The 245 is shorter (better for acceleration, into VANOS more), 2.4 lbs lighter, and width seems more suited on 9” wheel.

Is the 10mm extra width worth it for the 255? Doesn’t seem like it now that I’m looking closer …

[spidertri]

For track or Autox?

I'd run the 255 at Autox for the extra top end in 2nd gear.

At the track probably a 245 for the reasons you listed.

[Yvrbmw]

Autox. We have really small lots here so the top end is not much of an issue. Unsprung weight savings and feel are appealing

[spidertri]

Definitely depends on your club/site, down here I'd say every other event has a course that lets me hit the top of 2nd.

If you like the feel of a 245 on a 9 more, then go for that. I think a big part of it is you having the confidence to push harder. I'll probably try that size for my next set of track tires.