6" with a 3" hole. a quad rotor is about that size but they have a big hole. a dirt bike rotor is preaty big. like 10" and have a 4" hole. what you may need is a cr80 rear disk. i think they are about 6" or 7" and have a 3" or 3.5" hole. you should be able to pick one up at the local bike shop for about $60 new. if not i can try to find one for ya /forums/images/graemlins/waytogo.gif
thanks for the link thats what i need and in the right price rangetoo. i had originally planned on finding one close enough to tap the rotor and bolt through it. till i found this guys page. notice how he connected them. i will probably weld the mounts to it instead of just bolts though.