The studs are pressed through the rotor and into the hub. The spacer bolt then goes through the spacer, the hub and threads into the rotor.
I'm thinking that without the spacer bolts nothing is going to move once the wheel is bolted down.
I'm thinking Gregg is correct. It's to keep from losing it. I know people run front drums un-riveted. Are discs really so much stronger we need to bolt the spacer?
