what tire diameter difference is ok between the front and rears. i'm considering a front: 25.5" with a rear: 26.3". will that be ok for the awd system - in general what is the biggest difference recommended?

cheers,
boris

 

Generally you dont want to run anything off by more than half an inch. Some guys on this forum say its ok, some have had problems. I believe the manual says something about 4% also. You might want to look into that. If i were you, i'd just run "safe" sizes and stay within a half and inch difference. Good luck!

 

that seems like a bit much

 

.8 inches rolling diameter isnt much, but I wouldnt recommend it.

 

Absolutely not OK. Stock is 0.1", max I have read on multiple sources should be 0.3"

 

Is running 235 in front and 315/30/18's in the rear okay? I saw a 295/30 next to a 315/30 today and the diffence seemed to be no more than a 1/4".

 

Use this : http://www.miata.net/garage/tirecalc.html

 

I've been told by several sources that running GT2 sizes front and rear is fine.

 

I run 235/40 front and 315/30 rear (Ie GT2 sizes) and everything (AWD, PSM etc) works just fine.

Cheers,

Beej

 

It's 3.1%. According to Porsche stay within 4%. It's "legal", but I would not do it. Is the car lowered? If so it'll probably rub. Other factors such as wheel offset and fender lip rolling will likely come into play. Keep both ends as close to 25.5" tall as you can.