I'm considering upgrading from Avid BB5 to BB7 mechanical disk brakes on my fat-bike and upgrading to Avid Speed Dial 7 levers. While I'm at it I can easily move up a size or two from the existing 160mm rotors. The mounts are 51mm IS front and rear and there are no clearance issues apparent with the front fork -- it looks to be parallel well past the point that even 203mm rotors would sweep past.
Avid's come with adapters and am I correct in assuming that the adapters included for a 180mm rotor would correctly space the calipers out from the 51mm IS mounts?
Going from 160mm to 180mm would effectively increase the radius 10mm; going from 160 to 203mm would increase radius about 20mm. Is there any issue with rigidity or or alignment going with much larger adapters?