I have recently bought new wheels for street use from wheel enhancement and squeezed 315/30 and 235/40-18 Michelin Pilot Sport Ps2 tires in. Wheels are Silver 8x18" ET45 and 11x18" ET36 Victor Equipment Innsbruck rotary forged 1-piece.
The fit is likely perfect after I raise my relatively low 2001 996 Turbo slightly as the rears do not hit the fenders, but do hit the fender liners inside and outside on bumps.

I use the stock wheels on the track and am now buying Hoosier R6 to try to put the Evo GT 660 power down better on the track. Does anyone have experience what Hosier R6 sizes can be fit? I am thinking of going 315/30 rear and 255/35-18 front. Diameter difference is just over 3%. Can I, helped by the slightly smaller diameter, get the wider front tires under stock fenders and would you be concerned with the 3% diameter difference?

 

The 255's are wide but very short. You should be ok. Of course it may depend on alignment. More negative camber is good. You might need some hubcentric spacers though. I run 19mm.

 

Thank you, heavychevy.

Has anyone actually squeezed 255/35-18's in there? Hoosiers? Again, I am using stock rims (8"x50mm offset) and wonder if they will fit.

 

I run 245/40/18 with stock suspension and stock height with no problems..

 

Yes, they fit fine on my TT, but my car is aggressive so I can't say for sure if they will fit on yours.

 

I have 255/35/18 r888's on a 9.5 inch wheel with a 7mm spacer up front... Not one regret.

 

i own a 255/35 and its my everytime favorite among all the other stuffs

 

255's are just a tenth wider than a 275 but shorter. Best fit is 8.5-10" wide wheel.

 

Some feedback:
Fronts 245/40-18 Hoosier R6 on stock 8" wheels required increased room in front of the tire. We moved the corner radiators a little and flattened the fenderliners. I believe this would still be an issue if the car was not lowered. No rubbing after hard driving on Sebring.
Rear 315/49-18 Hoosier on stock 11" wheels. As the car is significantly lowered we are fighting to create the space for these wheels. With very little fender clearance, and hitting the fender liner inside and outside we will work on the liner some, and possibly raise the verly low car some. Also, the right rear hits the rear left fender liner on the inside low down by the turbo hose when the car goes airborne. Some moreadjustments, mainly of the fender liners, needed to improve the situatiion.

 

On a bumpy track like Sebring you will have to ride like a 4x4 not to touch the fender wells. That or put some super stiff springs and coilovers on.

 

I have PSS9 coilovers and adjust the shocks fairly soft on Sebring compared to outher tracks.
Clearance issues in the front were noticed and corrected before I went to the track so no problem there. The rear is hitting so evenly inside and outside. I may be able to reshape the fenderliners, or just raise the rear a few millimeters more.