Shorter tire means less distance traveled per a given RPM, as you note with the final drive statement. That means less speed for a given RPM, which means lower speed with shorter tires at redline. You're both saying the same thing, in different ways, I think.

But yes, I'd love to find a 255/45 or even a 255/50 if it had REALLY stiff sidewalls. I think the Z could use the torque reduction given the low overall grip of street tires, not to mention a couple more MPH for any given rev limit.

The low hp/light weight cars (S2K, miata) usually look to find something shorter to help them overcome their lack of low-end torque. I don't think we need that. I can spin the wheels at 30mph in second as it is coming out of a hard turn.

 

Everyone has a traction control device built into their cars. its called the "Gas Pedal." Intentionally reducing the available torque is not a good idea. What's needed is thinking out side the box.

Maybe a stiff sidewall 255/35-18 up front and a soft sidewall 255/45-17 out back? A focus on lateral grip and response up front and longitudinal grip and forgiving slip angles in back?

Remember, any of these tires you choose need to be shaved to 4/32nds to even be close to competitive. None of you guys are thinking about competing at a Divisional or National level on full tread depth tires right?

 

That's the commonly accepted wisdom, but a few tests ive seen show faster times with full tread depth tires, notably one from sportscar mag a while back. Of course you can only take tests for what they're worth, but they're worth something.

I would test both on MY car before going to nats. Hopefully I'll be able to get that done early in the season next year and go from there. I'll be running full depth tires locally though just because they are pretty fast and good for several hundred runs that way, and our local lot isn't high enough grip for the difference (especiAlly in transitions) to matter. For that matter, I doubt the XSs in general are stiff enough in the sidewall to be able to tell shaved vs full depth on feel alone.

 

Also, re the gas pedal; you're limiting applied torque either way. Building it in to the car makes the car easier to drive, and that means more consistent results. That's important when you only get 3 looks at a course.

Gaining more mph in first and second (on top of a raised limiter) also adds another advantage that more precise pedal modulation doesn't.

 

This is generally true if the driver is more comfortable with larger slip angles from the tires. This gives the driver more confidence and let's them push harder, which results in better lap times. But, all data acquisition I've ever seen regarding shaved vs. non-shaved (full tread depth) shows quicker response, more lateral grip, and less dropoff if the tire is shaved. The question is whether the driver can consistently (corner after corner, lap after lap) take advantage of that.

 

shaved tires are much quicker than non shaved. i drove on both this year driving other cars and to me, the difference between shaved and not shaved was very noticeable

 

Which tires? I'm curious to know in part because I've only driven the new XSs out of the 'fast' crop of street tires. Well, I drove the Dunlops for a couple runs in the wet on an under-prepped 95 M3, but that's my only reference point.

The XSs seem pretty 'mushy' in transitional feel whether full depth or not to me, both on my car and on an uber-prepped 97 M3 sedan I've driven a bit.

I'd be interested to know about the others (RE-11s, 'Kooks, Yoks, etc) if you have experience with them.

 

Hell I did that test and I know it was bunk. Any number of anomalies may have caused that - and we said so in the story - the surface we were on (likely), or the fact it was done with a stock class car. Full tread may be OK for local stuff, but you are nuts if you try to run them at a big event.

The Dunlops that were on my STX car at this years Solo Nationals were shaved to 3/32nds, that was worth a 2.5lb weight loss per tire, right there is reason enough to shave them. Shaved tires also resist overheating much better than full tread.

 

Also very good points, and I know you have the experience to back them up.

With my ongoing weight savings extravaganza, that 10lb savings in rotational mass alone (at the furthest point on the radius) is pretty awesome, indeed.

I guess I'll have to play with some shaved Dunlops next season, unless the money tree starts producing and I can afford to spend a week testing them all at Lincoln.