Quick tire question - Page 2 - 6SpeedOnline - Porsche Forum and Luxury Car Resource

Jul 16, 2016 | 11:18 AM

#16

Macster

Registered User

Joined: Jun 2009

Posts: 2,190

From: Benton County, AR

Rep Power: 147

Quote:

Originally Posted by Q..

As pointed out above, you will have a greater rolling diameter with the 295/30's
However, 295/30's will not cause an ABS / PSM fault.
I have used the 235/ 295/ combination on several 996TT's without issue.

If you want to see something a little extreme, this car

runs 245/30/20 & 305/25/20

Horribly over geared, which detracts from its acceleration, but still no ABS / PSM issues...

Stock tire chart:

Code:

Tire Size Comparison
Specification  Sidewall  Radius  Diameter  Circumference  Revs/Mile  Difference
225/40-18         3.5in  12.5in    25.1in         78.8in        804        0.0%
285/30-18         3.4in  12.4in    24.7in         77.7in        815       -1.4%

Curent tire chart:

Code:

Tire Size Comparison
Specification  Sidewall  Radius  Diameter  Circumference  Revs/Mile  Difference
245/30-20         2.9in  12.9in    25.8in         81.0in        782        0.0%
305/25-20         3.0in  13.0in    26.0in         81.7in        776        0.8%

Horribly over geared is not quite correct.

Horribly incorrectly geared due to tire size mis-match is more accurate.

With your tire selection you are not getting any AWD advantage and in fact since the front tires are making more turns per mile than the rears the front axle is acting like a brake through the viscous coupling.