I am fitting 15mm spacers on the rear for track days.Which is the strongest type: [a]spacer with longer bolts or [b] bolt on spacer with studs and nuts?I am not worried about locking bolt/nut for the short time that they will be on.Any suggestions?Ian

 

why are you adding spacers for track use?
it's preferable to have correctly offset wheels so you dont have to use spacers. and if you must, 5mm is the most you should use on track.

if you need wider track, you need custom offset wheels not spacers. and even if you use custom offset, when the center of the wheel is too far off the hub face, you will have problems.

 

Mooty,the standard GT2 wheels[18x12 rear]rub the tires against the inner plastic wheel well liner on a fast turn with bumps on it.I don't think 5mm would be enough to stop the problem.Ian

 

i dont understand.
if you have oem GT2 wheels on a GT2, there will be no rub, no matter how bumpy the road is or how fast you drive.

something is not right in your description.

and if you run 15mm spacer, you may very well rub the wheel arch lip.

 

Mooty,just took off the back wheels and sat them side by side with track wheels.On identical rims[OEM18x12 ET45]the Pirelli P zero corsa track tires have a slightly squarer profile than the Michelin Pilot Sport road tires.Being new the pirelli set up sits about 8mm higher when side by side.Back on the car I can get my index finger up to the nuckle between the tire shoulder and the plastic with the michelin.With the pirelli I can only get it in to the finger nail.I would say 6 to 8 mm difference.The plastic liner is hard against the hose coming out of the intercooler and won't move back at all.
I now think that a 7-10mm spacer will fix the problem[you are correct -15mm will make it rub the outer lip].I don't think that scrubbing tread off the tires will help as the part that rubs is on the shoulder just where the tread ends.

 

7-10mm spacer is ok, but more than that really isn't good.
sounds like your P0 is very wide: stock size?

 

Mooty,Yes,everything is stock.I have ordered 10mm spacers from Fabryce at GMG.