The reason I ask is I have changed the front width wheel size on the car, but I'm a little bit concerned I have issues with different rolling diameters as I have a the Tiptronic 996 Turbo.
The new width is 8.5" compaired to 8" (rears are still same) but my new front tire size will have to be a 255/35/18 compaired to 225/40/18 does anyone know if this is ok to run alongside the stock rear size?

 

If you compare the diameter, the 255/35 will be absolutely fine with the stock 295/30 rear size. I would be worried if it rubs to fender?

 

I have 8.5" w/ 235/30/18. fine no problems.

 

I have 8.5 fronts with 245/40/18 (RA1s) which have a little taller sidewall than most. There was somve very minor rubbing when approaching lock. The seem to be 'seated' now.

I think you will rub like crazy with 255s.

Mike

 

Mike, I think I would be in transmission trouble if I run 245's as the sidewall figure works as a percentage of the width of the tire and because i'm a Tiptronic. Even if I go for a Rolling Road (Dyno) It has to be mechanical linked, running in sequence or I will burn up tranny. The correct figure (closest to stock) would be 255/35/18, dropping the sidewall height but increasing the width slightly. Agree possible rubbing issue, but don't know how much.

 

The car gives you 4-5% tollerance in OD before issues start to arrise. Stay 225 or 235 on the front. Anything wider than 235 on on 8.5" doesn't give you anything back in street performance. I can't see how a 255 will fit and not rub under any circumstance and will need at least an 8.5" rim to fit. 9"+ is more ideal.

 

Thanks Damon, think I was more concerned regarding the 4wd system especially the Tiptronic as both travelling diameters are different (but not much) currently I'm using stock Turbo Wheels with 235/40/18 front and 295/30/18 rear, the stock front is 225/40/18 do you think this would have any issues?

I have a new set of wheels which are 8.5" front with 11" rear so the choice was to either go 255/35/18 fronts to stay inline with the 295/30/18 which would be fine but possible rubbing issue, so safest option is to go 235/40/18 for fronts and increase rears to a 315/30/18, this way it should all be safe regarding rubbing and rotation.

lol, hope that all made sense, lol

 

I had 235 hoosiers on the front of my car (factory 8" wheel). No rubby.

Oak, arent the factory GT2 wheels 8.5 wide in front?

MK

 

mk, yes 8.5" rim widths shod w/ 235/40/18. not 235/30/18 that is incorrect (what I posted above.)

 

235 is fine, 255, no way at all.

 

Stevo, what are you trying to achieve? Reduced understeer? If so, perhaps there is an easier solution, like putting an adjustable GT3 sway bar on the back and tightening it up. They are pretty cheap too.