Probably a stupid question, but I was wondering if there was any difference in the calipers for difference rotor sizes or is it just a different mounting bracket. Reason I ask is that I have 185mm rotors right now, but it is overkill for the application so I would like to loose some weight and rotational mass and move down to the 160's. Also, I had a pair of BB5's on an old bike and they seemed a lot lighter than the BB7's on my current ride...this is where my first question stems from. Thanks!!!