dmihalevich

I have a 2007 Turbo with 19 wheels. I have a buddy that has a GT3 RS and has switched to a different set of tires from the cup tires that came standard with them. I would like to use them for track tires but am not sure they will work on my car. I had a 996 turbo and there was forum after forum explaining how careful you had to be running different sizes to achieve a 1:1 rotation but I cannot find any info on the 997 alternate sizing. In addition I have read that the 997.1 is not as sensitive to a 1:1 but wanted to confim.

Stock 997.1 tires 19" sizing 235/35/19 front 305/30/19 rear

GT3 RS 19" Sizing 245/35/19 front 325/30/19 rear


DM

Igooz

245/35X19 = 25.75" height
325/30X19 = 26.67" height
3.57% difference

235/35X19 = 25.47" height
305/30X19 = 26.2" height
2.87% difference

The rule of thumb used to be stay within +/-3% difference to not over work the diff. But this topic has come up multiple times and no one really knows the right answer.

I am also assuming you are using the GT3RS wheels? If you are using the stock turbo wheels with these tires, the turbo rear wheel is narrower than the GT3RS rear wheel and thus with 325 you will get further "ballooning" and the difference will go up in the wrong direction.

**check my math**

dmihalevich

I am putting them on OZ racing Wheels, I believe the fitment is 19 X 11 in the rear. This would likely throw it off in the wrong direction. I may have to talk to the dealer. Thanks

DM

4ocious

I replaced my OEM 07 TT 19's with stock GT3 RS wheels. They fit fine and I had no problem/s.

Igooz

This is exactly right, they fit and they look really really nice...I agree...In fact, I have been fancying a set of those wheels for my 7TT.
What I just don't know are the affects of the extra front to rear height bias. Ask someone "techy". Maybe PM "gtgears"...

550bryan

Regarding the tire height difference I'm calculating a 1.1% difference on the fronts (.28 divided by 25.47) and a 1.8% difference on the rears (.47 divided by 26.2). This difference should be insignificant in terms of vehicle dynamics. I'm thinking about putting a set of this larger size PSS's on my stock 19" Cl's. I realize the tires will be slightly more bulgy but that's Ok with me and I think they may very slightly fill up the wheel well more fully. I sure would like to hear form someone who's actually done it though to confirm my suspicion.

dmihalevich

I dropped a PM to "GTGEARS" to ask. To be clear I am not using GT3 RS Wheels, just the tires. The wheels would be the OZ Racing 19 X 11's. I believe stock rears on GT3 RS is 19 X 12. I appreciate the feedback, thanks much.

jem7v

Could someone put GT3/2 RS wheels and tires on a 997.2 turbo S and be fine?

CincyScott

Yes

Igooz

Bryan...you are doing the wrong calculation. You want to see the difference in height between front height vs rear height on the same same of tires This tells you the front to rear speed difference.

Please post the answer...the question is what would be the front to rear (percentage) limit of tire height. I would love to know the facts too...

CincyScott

Just my opinion, but I think a 325 will be awful big on an 11" rim. A 305 MPSS looks awful big on an 11" rim, I can't imagine an almost extra inch to contend with.

Igooz

Yes, I agree with that...I would not put 325 on 11" wheels. I think that I said that before.
(Nevertheless, I may want to do the same tire sizes on 9" and 12" wheels...so I am still curious about the answer front to rear maximum allowable difference)

CincyScott

I just ordered those sizes for the 19 x 9 and 12 setup I'm putting on my car. Checked with Damon at tirerack and he said that was the right way to go.

Not sure if that helps, but it's another data point

CincyScott

Just a quick heads up, there's a nationwide back order status on 325/30/19 MPSS right now for at least 45 days. Mine are on hold

eurotom

I agree with the input that has already been provided. Tire manufacturers do not recomment a 325 on a 11 wheel. I belive minium width is 11.5.

@Cincycott- I agree a MPSS 305 with its large rim protector looks wide on on a 11" wheel but again I tend to follow MFG recommendations like not tuning my car, not lowering, not changing exhaust, sway bars, engine mounts shifters fluids etc

OP- there are plenty of guys who run a 325 rear on 11" wheel, how it looks is subjective however what the tire was designed to do is a different story.