Maybe someone should reiterate the basics.
Short reach: 39-49mm
Medium reach: 47-57mm
Long reach: 57+ mm
Short reach could vary. Some early aero brakes were more like 36 - 42 or something like that.
Medium reach was also called
standard reach or
normal reach. It's specs would also vary. For example the Weinmann 610 which unsurprisingly goes up to 61. Often incorrectly called long reach nowadays.
Long reach was sort of a catchall for anything bigger. Weinmann 750 was a ubiquitous and typical example.
WRT why long reach in the back? The only explanation I've ever heard was that the lower mechanical advantage of the rear brake made the brakes feel more balanced between front and rear. Maybe. I wonder if the actual explanation is more boneheaded, like to get more mud clearance, or maybe it was to make room for a bigger tire in back for traction. People used to think that way.
Originally Posted by
T-Mar
You measure perpendicular to the mounting bolt axis because that is how manufacturers measure and report their brake reach dimensions.
That is how I've always done it, and it was also my understanding that that's how manufacturers did it. Thanks for verifying I'm not nuts or gaslit.