Porsche413

Hi all,

I purchased a 2004 C4S 4 months ago with 4 brand new Pirelli P zero Rosso from a Porsche Dearlership (they had installed the tires). I have already logged in 5000 miles as it is my daily driver.

Today I just realized that I don't have the correct tires on the rear... Car came with front 225/40/18 on 18*8 wheels and rear 285/30/18 on 18*10 wheels.
If I am correct I should have 295/30/18 on the back (the good news is the wheels will fit my winter setup of 225/40/18 and 265/35/18)

So my first question is:
Am I harming the 4S differential with those tires in the rear knowing that there is a -1.41% diameter variance and that with 295's there would only be a -0.47%? I can already see that the rear tires have more wear than the front ones.

And my second question is if I have to change the rear tires can I install the 295 on the 10" width wheels? If I look at tire rack for the same Pirelli P zero Rosso it says the width rim range is 10"-11" but measures rim width is 10.5".... and do I have to change the front with brand new ones too?

Thank you for your help!

wildbilly32

Your reg wheels are 18 x 10? My 2005 996 C4S(actually produced in July 2004) has stock 18 x 11 wheels. Are these after market wheels? Fronts are the same as yours 18 x 8.

Book says for mine 225/40 front and 295/30 rear.

I don't know about range of diameter mismatch for front diff problems, but someone will pop in with that knowledge.

It is not unusual for rears to wear quicker than fronts. Having said that do you know if car was aligned by dealer after tires installed. If so, how did the readings look?

Porsche413

Hi, thanks for your answer, yes the back wheels should be 18*11 but mine came with 18*10 which I know should be 11", but they are stock Porsche wheels (might have pertain to a C2)... and yes alignment was done.

Dennis C