IF you talk to any Customer wheel builder .. EX: Stockton... they will tell you that you do not need to make any CENTER WHEEL HUB to rotor contact .. the studs is what centers the wheel when bolted down to rotor face ... How much material needs to be removed to give you the clearance you need ?
To go from 2 1/4" diameter to 3" diameter, i believe they would need to take off 3/8" all away around which would remove the lip of the wheel that I've heard gives a good deal of structure and rigidity to the wheel
