Ray,
I'll add just a bit to what has already been said (and most of which you already know but some new to the sport might not). If you need to know what brake length is needed for a particular frame, put in the chosen wheel and measure from the center of the rim to the center of the brake hole. This distance for the front and back often do not exactly agree. Custom frames vary in how particular they were with brake bridge placement. Now you match this measured distance with a brake that can accommodate that same reach.
In today's market, by far the most common brake reach distance is 39 to 49 mm. These numbers are often stamped on the back of the brakes. This is the measurement most common on Shimano and brands that copy Shimano. In the past (like during late on topic years) this might have been referred to as "short reach" brakes. New OT Campy brakes are a bit different in that their modern Record brakes are 40 to 50 mm and Centaur and cheaper models are 42 to 52 mm. The next most common size is 47 to 57 mm brakes. When Campy brakes first came out (about 1968), this was their standard length and are sometimes referred to as "standard reach" breaks. Later, to shorten up the down tube, 40 to 50 mm brakes took their place and the "standard length" were sometimes referred to as "long reach". Old Schwinn Paramounts used Weimann center pull brakes and these had more reach yet. I think they had something like 62 to 78mm of reach. That is why if the bike was being converted to Campy brakes, one of those "drop bolts" was needed. So you can see their is no standard as to what "long reach" brakes are since what is most common has changed to being shorter through the years and what is "long" keeps getting shorter.
Doug Fattic Niles, Michigan
Ray wrote:
"I am looking for a clear, understandable definition of long reach brake calipers. I need some kind of hint that will allow me to identify long from short quickly without mounting on a bike. Here is my issue, I have a bike that I am building up that I have what were called long reach calipers installed. With the pads in place they just barely reach the 700 rim and they are bottomed out on the arms. Perhaps the bike is meant for 27 rims and that is my problem. Any hints would be helpful."
Thanks
Ray Homiski
Elizabeth, NJ