Bicycle speedometers are small computers that attach to your bicycle to measure the rotation of your tires. The computer takes information from sensors located on your bicycle tire and calculates your speed. These computers often provide other information such as your distance, the time, your heart rate or the altitude. Installing a speedometer is simple even if you are not a bike mechanic, but you must program your computer properly to obtain an accurate speed from the sensors. If you are not confident in your ability to install a bicycle computer, take your bike and computer to a bike shop.
Attach the computer sensor to the fork opposite your brakes on the front wheel mount. You can attach the sensor at any point along the fork, so choose a location that will be easy for you to access. If your sensor did not include any specific attachments, secure the sensor in place with a cable tie.
Run the wire from the sensor up the back and outer part of your shock absorber. This location will protect the wire from branches or undergrowth that you may bike through while also keeping the wire away from the wheel in motion.
Attach the computer mount to your handlebars in a location that is easy for you to see. The computer's display will go in this mount, so it must be in a location that is easily visible. Every computer mount includes slightly different hardware, so secure the mount in accordance with your computer's design.
Secure the wire that connects the sensor and the computer mount to your bike frame with cable ties. Add a cable tie to any location where it looks like the wire may dangle or bow out from the frame. Leave enough slack in the wire so your front wheel and handlebars can turn freely.
Clip the included magnet to the spokes of your front tire in a place where it will pass by the sensor each time your tire rotates. The sensor knows your tire has made one complete revolution each time it senses the magnet, so it is vital the magnet passes within about 1/4 inch of the sensor.
Enter the diameter of your front bicycle tire into the computer. This information is usually printed on the tire itself or will appear in your bicycle's user manual. Your computer must know the tire diameter in order to calculate your speed accurately.
Turn the tire to ensure the computer sensor is detecting the magnet as it goes by. Your computer display will show a nonzero speed value if the sensor is working correctly.
Test the accuracy of your speedometer by cycling next to someone who is also using a bike computer. Your speeds should roughly equal the speeds the computer displays. If the information is substantially different, you may have made an error when inputting the diameter of your tire.