Porsche uses 5mm spacers on the 12 inch wheel for the GT3 - 5mm looks like this __

 

No problems with Porsche had dealer install when car was in for service. OEM Spacers and bolts so no worries. Never track car so can not comment on track performance.

 

7 front, 15 rear commonly used with no problem

 

Thanks for all the replies!

So, looks like the rear will be ok, and with further investigation the front will only be 3mm further out than a GT3 too.

Only slight doubt remaining is that the GT3 suspension is noticeably stiffer, and not sure the wheelarch clearance is ever an issue.

I've also sent the question to Porsche Germany, so will see what they come back with, but you have to assume that if Porsche fitted them to 72offsuit's car then it can't be an issue.

Thanks again.

 

Wheelarch clearance is not an issue using 7&15mm spacers. Remember the GT3 rear wheel is .5" wider on each side.