Hi,

I am new to the community and upon my searching attempts reargarding the how different wheel/tire diameter as OEM spec would have its affects on the all-wheel drive system. Excuse my newness and please point me to the right direction, I thank you in advanc.e

Points of concern:
Is keeping overall diameter for both front and rear tires a must? If not would the center differential be damaged or affected negatively?


I believe my OEM wheels are 19x8 and 19x11 with 235/30/19 and 305/30/19 respectively. I plan to run a set of wheels and tires from GT3 RS fitment. They are fikse 18x9 and 18x12 with 235/40/18 and 315/30/18 tires. Front overall diameter are on point however the rears are 3% smaller in terms of overall tire diameter and this is my main point of concern. I need to know if I can run the 18 inch wheels safeley and if the brakes would clear.

Coming from the subar background, their center differntial requires all four tires to be within 3/32 tread of each other. However I am new to the all-wheel drive system of Porsche which also came in staggered setup which confuses me even more so any help would be appreciated.

Regards,
Ethan

 

Your OEM wheels should show the rim widths and offsets on the wheels. My T4S has the Carrera Sports, which are 8.5" front and 11.5" rear rim widths, with 235/35/19 on front, and 305/30/19 on rear. I'm not sure what the tolerance is for size changes on the AWD cars.

 

Ethan....no need to excuse yourself......good to have ya here.

Starting back w/993 C4 and carrying forward to C4 996 & 996Turbo the general point of ref was 3% or less differential front to rear...these cars I know cause have & bought multiple fitments for each.
I guess I'd assume 997 to be similer (though my 1st hand experience on same won't begin til I shop for wheels for my in-bound 09). Anyone w/dif info please enlighten both Ethan and myself.
OK and ..... it's often refered to as 'rolling diameter'.....not sure why, cause it's simple circumference.

Only other word of advice I'd throw in.....my rule is 1st consider and decide what you plan to run for rubber .....then find (or have made) the appropriate fitment.
You buy alot more tires than wheels.......and in the end, the former is the larger investment......probably the more important.

Good luck to ya.

 

Welcome to the six! Post some pics of your ride-

IIRC, you want to stay within 3% or 4% of stock overall diameter.
Since the 997 base model cars ship with 18" rims standard, take a look at what size rubber they are running on the 18" rims. That sould give you a good point of reference.