One issue with this system is that the factory 18 inch Bullitt wheels have insufficient backspace for the monster Brembo calipers. I knew of this before I started and was faced with the choice of replacing all the wheels (and indeed, I have a set of GT500 wheels ready to go, but that meant 4 new tyres and pressure sensors etc. - that and I prefer the style of the Bullitts!) or using spacers. Now, some people are uncomfortable with using wheel spacers, but providing they are of good quality, hub centric and securely attached, there's no problem. The set I bought was from Driftworks in the USA. They are 1 inch (25mm) spacers which use the original hub studs to attach to the hub, then a new set of studs to attach the wheel. The wheel spacers I bought were a perfect fit, really snug on the hubs (they are hub centric, so they centre correctly on the original hub) and indeed, had to be snugged up with the mounting nuts. To be safe, I used blue locktite on them too as I have little intention of removing them again. The only issue is that the original hub studs are about 5mm too long to fit into the pockets in the back of the Bullitts. The solution? Well, out with the hacksaw/angle grinder and carefully take 5mm off each stud. The wheel then fits perfectly but man, it's CLOSE! Close to the extent that you may need to remove/replace/move the wheel balance weights as they may rub on the calipers. Cue lots of filing of mine (and the factory Bullitts seem to have LOADS of weights on them) until the wheels rotated with no interference.