I understand, I'm both fairly intimate with the rules (I'm on the SAC) and with sway bar use. As you know, sometimes you need less bar as you go from A6s to street tires depending on the application. The 997 I drove put down power fine and slalomed well, I just wanted a bit less throttle on understeer so I think that could have been solved with less rear toe and no other changes.

Tom R

 

At present, I am running 275/35-18 ZIIs and 275/30-19 AD08s. Being a mid-engine car, the Cayman has less rear weight bias (and also less power than a 911 ... grrr), so the 275 width seems to be adequate (although I haven't actually tried a wider rear tire, so who knows?) That said, I am considering trying a 295/30-19 rear tire the next time around, although perhaps not for the reason you might think.

The Cayman has a stock tire diameter stagger of ~.9" in favor of the rear tires. Although many people are able to run same-diameter tires (i.e., 285/30-18) front and back, experience has shown that my car starts suffering ABS / PSM issues once the diameter stagger falls to .2" or less due to tire wear (because the rear tires wear twice as quickly as the front tires.) I suspect the same is likely true with your 911 as well, but don't know this for certain...

If I don't go with a wider / taller rear tire, then I will instead shave the front tires to a 6/32" tread depth and make them .25" shorter, which should be sufficient to preserve a minimum .4" of stagger down to the wear bars. So far, this issue with stagger has been limited to only the 19" wheel / tire combo, as the 18" wheel / tire combo started with slightly more stagger (.6" v. .4") and is only half-worn at this time, so the diameter stagger is still at an acceptable .4"...

 

FYI, I'm a big fan of Champion wheels -- I have two sets of 19" RG5s, one for DD use and the other for autocrossing -- and just bought a set of used 18" Champion RG5s after a year of searching (as you'll soon learn, sets built around 18x10 rear wheels instead of 18x11s are uber rare and those with a 911 offset -- ET58 -- instead of a Boxster / Cayman offset -- ET38 -- are even more rare still.)

Therefore, I am selling my anthracite-finish O.Z. Alleggeritas (18x8.5 ET53, 18x10 ET 65.) If you might be interested in them, send me a PM...

 

Don't rule out running different brands front and rear. Just mentioning the possibility will prompt a dozen internet know-it-alls to declare that that will make your car an undrivable mess, but in reality it's perfectly viable and in some cases arguably even preferable.

 

Upon reflection, when you wrote that you are planning to use an 18x8.5 front wheel, you were referring to applying the Street Class +/-1" diameter allowance to the option code XRR wheels, correct? If so, then ignore my comments above about the rarity of used 18x10 Champion wheels, as the most common 18" size I found when I was looking was 18x11.5, which is just fine for you, but much too wide for me.

 

Unless you're aiming for contingency money, in which case this is usually not allowed.

But I do agree that it can work very well indeed, as I have done it myself in the past. I haven't tested it yet with the Cayman, but it's on my list...

 

Oh yeah -- it's safe to say that you won't get contingency from either of the brands if you run mixed sets front and rear.

 

FYI, Hankook's RS-3 comes in a 255/35-18 at 25.0" tall; a 265/35-18 at 25.3" tall; and a 285/35-18 at 25.9" tall. Any combination of the first two with the last should provide enough diameter stagger to avoid any ABS / PSM issues and all of them are nominally wider than the Rival. Also, if you are willing to go with a taller-than-OEM rear tire, there is a 305/30-19 that is 26.3" tall available that you could run with 18" fronts.

 

yes, that is exactly my plan "applying the Street Class +/-1" diameter allowance to the option code XRR wheels"... my only concern is with the 11.5 rear wheel. I know that for track use, the larger 305 or even 315 width is desirable. However, I've read that some GT3 AutoX guys prefer a 285 on the rear. Not sure why it's faster, maybe a gearing advantage from less diameter or maybe it helps offset the inherent understeer issue with these cars. So, my concern is with putting such a narrow tire on that of a big wheel + the extra wheel weight. I did submit a question to the SAC asking if I can run the XRR optional 8.5 front with the stock 11 rear but I believe I already know the answer to that question...

 

GT3 gearing is astronomically high. They do it to shorten it up.

 

The problem I have with the RS-3's is it only comes in the 140 treadwear rating for those sizes. That's fine for next season, but because we have to go to UTQG 200 or greater for the following year, I'd have to switch tires again and likely start the set-up process all over. But still, 2015 is a long way away and who know what 2014 will prove out. There is so much controversy over the new rule changes I think it's reasonable to assume that more changes could happen.

 

The odds are so high that there won't be any rule changes in the next couple years other than to fix oversights as everyone involved wants stability.

There will be no RS-3 140tw soon.

 

Actually, according to Tire Rack's website, this is only true for the 255/35-18 tire; the 265/35-18 and 285/35-18 tires are both available in a TW200 version.

I understand your concern, as this is also why I haven't bought a set of AD08Rs, as I would prefer to develop the car around a TW200 tire that can be used beyond 2014 and having just released the tire earlier this year, it seems very unlikely that Yokohama will be revising it before 1/1/2015.

I believe it's a pretty safe bet that we won't be seeing any rules changes in 2014, only car reclassifications (or so I hope!)

 

I've heard ZIIs handle overtiring better than RS3 and Rivals. Anyone done any experimenting with that? I haven't had any issues with 225/45R17 ZIIs on my 17-7 front wheels, but I don't really have any points of comparison.

 

The RS3 don't like being squeezed and I have heard the Z2's don't mind. The Rivals dont mind, just need extra pressure when you do.