i noticed the new 997 tt comes with the following tires. my question is - how does the car run with the tire diameter differential of 25.5 to 26.3? isn't that too big of a differential?

235/35ZR19
Overall Diameter: 25.5"
Revs/hr 817


305/30ZR19
Overall Diameter: 26.3"
Revs/hr 788

 

Good point fly!!

Stock Tire - 235/35R19 >Search Tires Tire 1 - 305/30R19 >Search Tires Section Width:9.25 in235 mmSection Width:12.00 in305 mmRim Diameter:19 in482.6 mmRim Diameter:19 in482.6 mmRim Width Range:8 - 9.5 inRim Width Range:10.5 - 11.5 inOverall Diameter:25.47 in646.93 mmOverall Diameter:26.20 in665.48 mmSidewall Height:3.23 in82.042 mmSidewall Height:3.60 in91.44 mmRadius:12.73 in323.34 mmRadius:13.10 in332.74 mmCircumference:80.01 in2032.2 mmCircumference:82.30 in2090.4 mmRevs per Mile:816.6Revs per Mile:793.8Actual Speed:60 mph100 km/hSpeedometer1:58.3 mph97.2 km/hSpeedometer Difference: -Speedometer Difference: 2.872% too slowDiameter Difference: -Diameter Difference: 2.79%

 

what brand and model are the 997tt tires?

 

I believe that the are the michellin ps2

 

I'd say that if the 997s brain is set up to recognize a 4% differential (or whatever) as normal or reference.......then all would be fine

 

so can you run that setup on a 996tt???

 

I realize ideal for the 996TT is as close to 0% difference as possible but does anyone know what max % allowable diameter difference is? Given the 997TT currently allows 3%.

 

I'm with Gregg.

PLUS the 997 has an electronic AWD activation mechanism, so no viscous coupling to overheat. Basivcally it's 100% RWD until AWD is engaged.

The 996 Is 99% RWD until AWD is engaged, and even then not much torque makes to the front. Enough to make difference, but you will NEVER get the front tires spinning on a 996 in the dry.

 

So here's what I want to do... I want to keep my 225/40/18's up front and replace my rear 295/30's with 315/30's I just picked up from "paulycw" today. I calculated %difference and it comes out to be 1.4%. Based on everything I've read this is acceptable. Has anyone done the same?

 

should be fine. get 235s in front if you can later.

I have a set of 255/35s mounted on stock fronts in the garage that I have never tried for fit. Should really help the understeer.

 

I currently run 265 front and 335's rear on 18's

 

Ari, well as soon as saw your reply back I got them put on and the 315's look awesome... I drove the car just now to LA and back to Irvine and it feels pretty good no noticeable ride changes. I'll be looking to replace my 225-40's for some 235-40 Pirelli PZero Rosso's to match the rears. %Difference will then be 0.15% per the GT2 setup. Will keep an eye out in the forums and tirerack closeouts.

 

Tom did you have to roll your fenders for the front? On what wheels?

 

Tom, what aspect ratio? I assume 265-40's and 335-30's. Is this correct? That would be a 1.67% difference in tire diameters.

 

The difference in height should be less than 2% from OEM and less then 2% front to rear