langg

Another tire size question:
The recommended tire size for the rear of a 2001 C4 is 265/35 ZR18. The recommended size for a 2002 C4 is 285/30 ZR18. The 285/30 specs say it is 0.5 inches smaller in OD and 0.7 inches wider section.

My question is: with the same wheels, can I fit the 285/30 without any clearance problem?

Thanks,
Lang

Sneaky Pete

Yes they will fit. I have 295's on the rear and they are fine.

Zebrex

Your car is 4wd, I would be concerned with the front and rear tires being different diameters. If the rear tires are .5 shorter then it will cover slightly less ground in one revolution than the tire that is .5 larger. I dont know if .5 is enough of a difference to upset the 4wd or not.

Long Islander

The height of 265/35 tires is 642.7 mm. Your front tires are 225/40, which are 637.2 mm, so the difference is 5.5 mm, or about a fifth of an inch higher in the rear. With 285/30's, the height is 628.2 mm, or a difference of 14.5 mm (just of over a half inch difference) in the other direction. I have 295/30 rears with the same front, and the height is 634.2 mm, and this is the recommended size for my setup. I would try to use 295/30's, but you need to make sure they will not rub with your wheels. I have Sport Techno wheels, which I believe are wider than yours. Mine are (18 x 11 with a 63 mm offset) and if you have factory original 18" wheels on a 2001, they should be 18x10 (I don't know the offset).

You should check what your wheel size and offset is. Depending on the offset, they might rub the inside of your fender wells with 295's, but that is easily remedied with spacers. Once you know what your wheel size and offset are, you can go from there and figure out if you need spacers and what size.

langg

My wheels are 18x 10 with 65mm offset in the rear. My question was the clearance of the 285/30s on a 2001 c4 since the factory size recommendation is the same for the front for both (225/40). The recommended wheel size is the same for both also (18x10 w/65mm OS).

dgjks6

Porsche has a TSB on this. Up to model year 2001 the TSB recommends rolling the fenders to get 285/30's on the rear.

langg

OK. Thanks. That is exactly what I wanted to know. The rear fender clearance changed in 02.

Lang

Peter_S03

I have 285/30/18 on my 01 C4, changed from 265/35/18, I prefer the larger size. Fit fine all around with 225/40/18 front

Dennis C

The recommendation for the AWD system is that you keep the wheel/tire construct diameter for the fronts and rears close to the same size. I believe the "acceptable" variance is 3% or less. If you go beyond that, then there could be damage to the viscous coupling in the AWD system with long-term use.

If you use the standard front size of 225/40 R18, then your overall diameter for your front wheel/tire construct is 637.2mm as mentioned above. The 285/30 R18 wheel/tire construct has an overall diameter of 628.2, for a difference of 9mm. This represents a difference of only 1.4%, which is within the recommended variance. Your bigger issue will be the potential for rubbing, as mentioned above and as mentioned in the Porsche TSB. The TSB provides the dealer or mechanic with the steps to allow for this tire combination to be used without rubbing.

Long Islander

Lang,

I too was concerned about having to roll my rear fenders when I bought my Sport Techno wheels (I have a 2001 NB). It think it depends on which wheels you have.

Use this tool to compare your 18x10 65mm offset wheels to my 18x11 63mm offset wheels.

http://www.1010tires.com/Tools/Wheel-Offset-Calculator