[trularin]

Take an edge off the lip of the fender and measure the distance from that edge to the face of the rotor ( where the studs are ). Then subtract 1/2".

I hope I got that right, it's been a while.

Goofy as this sounds, you can make a model of your tire setup with a sheet of cardboard and bolt/tape it to the rotor. Then you can see if there are clearance problems. Once you are done, you can just measure what you have.

Just my $ 0.02