How To - Calipers Reach
Reach is the effective length of the arms of a caliper brake. This is measured from the centerline of the center bolt diagonally down to the middle of the brake shoe. Reach is commonly expressed as a range (allowing for the fact that the brake shoes are adjustable, typically 10-15 mm).
Reach dimensions can run anywhere from 39-108 mm. There has been a historical trend toward shorter-reach brakes, as newer bicycles, particularly racing-style road bikes, are designed for use with narrow tires and without clearance for fenders.
The reach required for a particular installation depends on the frame construction (how low the brake mounting holes are) and the rim diameter. Generally, shorter-reach brakes work better, due to the reduced potential for flex and the higher mechanical advantage. Long-reach brakes must be of especially stout construction and have long arm extension between the pivot and to the cable attachment to overcome these problems. Cantilever brakes and disk brakes avoid these problems, though they have other problems.
The images below show how to measure the reach you require
|This caliper has a reach range of 39-49 mm. As shown, with the brake shoe adjusted all the way up, it measures 39 mm from the center of the bolt to the center of the brake pad.||This fork and rim combination call for a brake caliper that can be adjusted to provide a 45 mm reach. The caliper shown would fit.|