Originally Posted by
jimc101
It's much easier to go larger than smaller, if the frame / forks have a post mount, you are most likely limited to 160mm smallest, 203mm largest via Post to Post adaptor.
Post mount is becoming the standard mount, it already is for forks, and is slowly going that way for frames, all disc calipers are now post mount, and use adaptors to go IS.
What is the need for going down to 140mm? this is almost a dead size, Shimano only ever did it in XTR, and Avid still persist with the BB series, but road disc when they come out will most likly be F180mm/R160 for modulation, killing 140mm forever.
i just got my crux with 140mm rotor on the rear the other day. already dislike it. not enough power combined with the long full length housing run. frame has no clearance for 160mm. the front 160mm is fine for road duty. i like my brakes powerful with low hand effort