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Old 11-20-2011, 01:31 PM   #8
thstone
Certified Boxster Addict
 
Join Date: Nov 2010
Location: Los Angeles
Posts: 7,664
Yes, the 225/45/17 on the front is the way to go. This combination of increased width and lower profile maintains the stock tire diameter of 25.0". If the diameter changes, then your speedo will be off and it might affect the ABS system.

Now, let's look at the rear tires:

255/40/17 = 25.0" (stock rear size has same diameter as the fronts)
265/40/17 = 25.3" (too big)
265/35/17 = 24.3" (too small)

To keep the diameter the same, the next matching size tire is a 285/35/17 (= 24.9" which is close enough). However, a 285 is a bit too large for the stock rear rim.

Thus, we are all kind of stuck with the stock rear tire sizing unless you go to aftermarket wheels.

Here is a handy tire size calculator: Tire size calculator
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1997 Spec Boxster BSR #254
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