I want to run a slightly taller tire in the rear. Its .6 inches bigger in diameter. Wonder if Porsche Stability Mgmt, traction control or ABS will have a fit? Appreciate thoughts but really would value someone who knows or has done it . thanks gents.
I have a '01 TT and would like to run 305/30 x 19 (26.3") rears and 225/40 x 19 frts (26.1"). Second question is do I have clearance with a 26.1' diameter frt tire, rears will be no problem.
Also someone mentioned a 3% rule or you'll kill your viscous 4x4 coupling GUARANTIED.

 

The rolling diameter of your tires is in spec. I can't say if they fit though.

 

I would love to know answer as well. Want to run Hossiers on 19 insch wheels. But the rolling diamater is 26 inches (measured on 10.5 inch wheel, so probably less on an 11 inch wheel). Too expensive of an experiment. Car is lowered as well.

 

I run 225/40/19 on the front, the measured circumference is 83". When turning to full lock the tyre just brushes the forward plastic louvered liner.
A larger diameter tyre would rub the liner.

The rears are 295/30/19 and the measured circumference is 83". There is plenty of clearance here.

Incidentally, the calculated revolutions per mile is 763 for both front and rear tyres.

 

X50, is my '01 TT suspension different than yours? Are the X50 clearences more than the '01 TT? I too would like to run 225/40 x19 on the frt, but my finger check indicates this larger tire would rub the fender liner and possibly the upper strut spring base. I'm currently running 235/35 x19 that have a 25.5" diameter vs 26.1" for the 225/40x19(according to TireRack that would be 798 rev per mile).

 

X50, is your car dropped or stock suspension height?

 

kennyPride - z99

my x50 has standard 996 Turbo suspension and clearances [and let's not delve into the "how can you tell an x50 turbo", thread.] It's not lowered.

Your finger test is correct, the 225/40/19 tyre is near the liner; with the wheels straight there is 1" clearance at the for'd side and more than 1" at the aft side. When the wheels are turned to full lock, the corner of the tyre just brushes the liner but to no ill effect.

Depending on the wheel off set, there may be interference with the suspension. I use 15mm spacers in the fronts but this is to give more clearance between the spokes and the brake calipers and bring out the wheel a bit for looks. Without the spacers there was only about 2mm clearance, I ran like that but was not happy. Depending on your rims you may or may not need spacers. I expect that if you have the oe rims you would not need spacers and the 225/40/19 tyre would be ok - but may depend on the tyre you select.

The liners are plastic, it may be possible with judicial use of a heat gun to reform the plastic a little to give more clearance.

the TireRack revs/mile of 798 i expect is a calculation and correct. My figure of 763 was calculated from actual circumferential measurements of the tyres i have on my car - Vredestein Ultrac Sessanta. I believe the measured circumference of properly inflated tyres varies by a small amount from tyre manufacturer to manufacturer for the same claimed tyre size. Even a small variation can produce a notable difference in revs/mile.

 

Revolutions per Mile.

For what it's worth -- Just checked the TireRack revs/mile for the 224/40/19 tyre, i calculate 772.8 not 798 quoted above.
This is only 10 r/m more than I calculated for my tyres using the actual tyre circumference - as opposed to 25 for TireRack.

 

Correction - above should read 225 - not 224.
Incidentally, I do have the 2 front Vredestein Ultrac Sessanta 235/35/ZR19 tyres I had on the car and changed them after less than 500 miles to the 225/40/19 for a better revs/mile match with the rears. They are speed rated up to 186 mph.
They are $160 the pair plus shipping from 70056.Attachment 457492

 

x50, thank you. Having the same stock suspension set-up and wheel/tire size I would like gives me some hope, but you're right the wheel offset can and will make a difference as the tire swings around in a turn. I may have to modify my fender liners, but my main concern is the strut towers (funny on the left/frt I have ample room but the right/frt is tight (maybe a 1/4" clearance with finger test with 235/35 x 19 at the tire and lower spring support. Is yours like that too?

 

KennyPride

You are right, the left strut tower is about 1/4" away while the left is more - maybe 5/8" - 3/4".
That is with the 15mm spacers. However, there is no indication of rubbing on the strut tower, but as far as i remember there was no rubbing without the spacers................................!
Do you have spacers in there?

 

Correction. the above should read............................

You are correct, the right strut tower is about 1/4" away while the left is more - maybe 5/8" - 3/4"

 

x50, no spacer but my wheels might have a little more offset as there is ample clearance by the brake calipers. I'm running 8.5x19 frt and 11.5x19 rear (3 piece Kinesis forged wheels).