Keep on climbing
Join Date: Apr 2004
Location: Marlborough, Massachusetts
Bikes: 2004 Calfee Tetra Pro
Bike computers are simply devices that display your current speed, distance traveled, etc. They're basically a combination odometer / speedometer for your bike. Most have the same basic features: current speed, average speed, maximum speed, distance traveled, time ridden. The more you spend, the more features you get: i.e., some will display temperature, altitude, cadence, heart rate... -- you name it, you can find it.
They consist of three parts: there's a magnet that's mounted to your front wheel, there's a magnet sensor that's mounted to your fork, and there's a display that's mounted to your handlebars. The computer is tracking how many times the wheel is going around (courtesy of the magnet), and then through a little math, it can then display how fast you're going.