Cal Club Autocross Forums

read something about maintaining the diameter ratio front to back to avoid TC and AH issues, but I turn that completely off anyway so not sure if it matters.

It will matter if your driving to events on them. You'll have to turn the traction control off for street use. The computer can't handle more than about 5% difference in diameters. I don't know if that is measured as a difference between the front and back or just a pre-computed expected diameter. I believe if the rears are substantially shorter than stock the traction control will think they are spinning and will cause activation of the TC.

Kristoffer Gjevre wrote:

Gary Thomason wrote:...
The 305 pretty much solves this issue. I just wish it was shorter!
...

So what is considered the ideal max speed in 2nd?

There isn't a (legal) tire short enough to get the GT3, C6 Z06, or Viper down to their "ideal" 2nd gear max speed in Solo, if there were such a thing. They're all 10-15mph too tall for SCCA National-approved courses.

Gary Thomason wrote:
Because of the huge rear weight bias, putting power down is never a problem even with the rear bar at full hard - unless (ironically) the too small 285 rear tires are overheated. This happens within about 35 seconds on a normal Socal day on a 285. The 305 pretty much solves this issue. I just wish it was shorter!

In SP, I would definitely run the largest tire and wheel that will fit under the front fender, and like the Evo, 285 is really the limit there.

i was leaning more towards a 245 being too small rather than a 315 being too big.

so if you can put down all your power all the time, why the big fear of AWD? }:)

Marshall Grice wrote:so if you can put down all your power all the time, why the big fear of AWD? }:)

Don't make me bust out the thrust graph again Marshall..

Jason, do you 315, 325 or 345 on Viper? That's a good example of a long geared car and the tire choice.

Rad_ Delgado_ wrote:Jason, do you 315, 325 or 345 on Viper? That's a good example of a long geared car and the tire choice.

On Kumho V710 I run 315front/335 rear
On A6 I've run 315front/345rear and 335front/345 rear
Stock is 18" 275 front and 19" 345 rear

I don't really have any gearing choices to make, the way the GT3 does between the 285 and 305 or 315. Hoosier used to make a really tall 315-19 that would make first gear (which I use about 60% of run duration on concrete) good for a few more mph, but I don't think the width tradeoff would be worth it for so heavy a car. They don't make that tire any more so it's moot.

A 355/20-19 would be great on the back of the car. Instead of 89mph in 2nd, it'd only do like 83...

Well the consensus (after talking to a few GT3 owners) is 255/315.

To prove the point, last year at the Toledo ProSolo, a bone stock SS 996 GT3 (Randy's car) driven by alien-like Braun spanked everything but one car in ASP. Mike "Junior" Johnson stayed away from the carnage by a mere 0.2 secs, the ASP cars included Collet, Stemler and Carpenter all of them with a National Championship in either ProSolo or Solo.

The lousy 996 GT3 is the same car that blasted the SS field last year at the El Toro ProSolo, with a lead of around 1 second per side over top National Champion drivers in SS.

This specific 996 GT3 is running 255/315, around 3,060 lbs due to the special heavy full power seats, full leather interior, and steel brakes.

I wonder how the 2010 997 GT3 RS with a few ASP upgrades would do at a Pro.

In the last 4 weeks, 4 SCCA autocrossers bought 997 GT3, with more to come. Cool !

So, for the 2010 El Toro Pro, shall we hand the trophy to the guy with the GT3 and save him an axle?

Rad_ Delgado_ wrote:So, for the 2010 El Toro Pro, shall we hand the trophy to the guy with the GT3 and save him an axle?

No doubt the GT3 is the best SS car at a Pro, and Gary the best driver, but no free trophies will be handed out. Perhaps if the rest of SS is lucky, we can talk him into finding a Z06 to drive instead...

Why the interest in SS Rad? Are you putting together a SS GT3? You may have found a consensus amongst the people you talked to, but considering the 2 SS National Championships by GT3s have not been won on that combination, I have a feeling your data set is a bit incomplete. Besides, even if there was a consensus, it wouldn't be directly applicable to anything other than a 996 GT3 in SS, certainly not a Cayman or 997 GT3.

Einstein once said, "Everything should be made as simple as possible, but no simpler." The effort to reduce these things to absolutes will only lead to frustration and confusion.

Rad_ Delgado_ wrote:So, for the 2010 El Toro Pro, shall we hand the trophy to the guy with the GT3 and save him an axle?

I happen to think this is a dandy idea :gpower:

Jason Rhoades wrote:No doubt the GT3 is the best SS car at a Pro, and Gary the best driver, but no free trophies will be handed out. Perhaps if the rest of SS is lucky, we can talk him into finding a Z06 to drive instead...

Spoken like a guy who is well aware he is likely to win at the Pro in that evil Dodge, making the guy in the GT3 force the issue at the starting line until he throws pieces out the back of the car. How 'bout doing SS a tiny favor and at least put the alignment back to where it was the first day in Nebraska?

Gary Thomason wrote:
Spoken like a guy who is well aware he is likely to win at the Pro in that evil Dodge, making the guy in the GT3 force the issue at the starting line until he throws pieces out the back of the car. How 'bout doing SS a tiny favor and at least put the alignment back to where it was the first day in Nebraska?

You just better be within .2 of ASP or Rad is gonna remind you that your tires are the wrong size...or worse }:)