dalter2
dalter2
3/7/23 6:34 a.m.

At my local autocross I am briefly running up against my rev limiter 1-2x per lap on my 245/40r17's.  I can switch to 255/40r17 to reduce my effective gearing and gain a little more top end speed and keep off the rev limiter......but will I sacrifice effective torque and therefore acceleration on the other elements and end up being slower overall?

Floating Doc (Forum Supporter)
Floating Doc (Forum Supporter) GRM+ Memberand UltimaDork
3/7/23 6:54 a.m.

How long are you on the rev limiter in total per run? If you're just touching it momentarily at one spot, that's a lot different than bouncing off of it for seconds at a time. 
 

Since you're essentially coasting while on the limiter, it's almost always better to gain a bit of tire. 
 

 

dps214
dps214 Dork
3/7/23 11:25 a.m.

With how short the stock gearing is, a bit taller is almost always better; 255s are what all the fast people are running anyway. We had 235/40s (shorter than stock IIRC...not what I would have chosen but not my car) last year and at nationals the east course was like 30% rev limiter but never in situations where shifting to third was reasonable so that kind of sucked. This year we swung way the other way with 245/45s. Haven't tried it out yet but it definitely fills the fender opening out better.

As a note, I have no idea what your setup is but if you have stock or stock offset wheels you'll need the full 7mm spacer allowance to make the 255s fit, which will require longer wheel studs. If you already have longer studs and/or lower offset wheels, then it's not an issue.

bobzilla
bobzilla MegaDork
3/7/23 11:28 a.m.

Reality is it doesn't matter. You're talking about a 1% change. At 60 mph that's 60.6. 
 

edit: if you stepped up to a 255/45 that's about 3mph (5%). 

trucke
trucke SuperDork
3/8/23 2:51 p.m.

Are you in the torque curve on the lower speed corners?  Will the taller tire still be in that range, then go with the taller tire.

bobzilla
bobzilla MegaDork
3/29/23 8:43 a.m.

In reply to trucke :

a 1% change isn't enough at autox speeds to matter. 

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