Odometers are always incorporated into bicycle computers. They measure overall distance traveled and up to 20 other functions including time of day, trip distance and speed. They work by counting wheel revolutions via a small magnet attached to the wheel. The data from the wheel are transferred to a small computer attached to the bike's handlebars where they are displayed on a small screen. Problems can occur through wiring, batteries or other malfunctions.
Magnet and sensor placement is a reoccurring problem for bicycle odometers. To accurately count wheel revolutions, the magnet must pass within a few centimeters of the sensor. The sensor is placed on the bike's fork and the magnet is placed on the spokes. When the wheel revolves, the sensor registers each time the magnet passes it. Sensors are usually attached to the fork with a small plastic strap. Magnets attach to the spoke using a small clip. It's very common for the sensor or the magnet to get bumped, moving them apart just enough to interrupt the signal, causing the display to default to zero because of lack of data. If your screen goes blank, or fails to register any data, always check the magnet and sensor alignment. If it's off, just move the magnet and sensor back into place with your fingers.
Odometer display screens are made for easy removal. The display slides off the mount easily and should be removed if the bike is in transport on a bike rack, or in wet conditions. The mounting device is not always fool-proof and if the display screen is bumped or isn't clipped in properly, the screen can come off and get lost. If this happens during a ride, chances are you won't see it as it goes bouncing down the highway. Check the stability of the display screen by clicking it forward and back before you ride to ensure it is properly attached to the mount. On mountain bikes, if you are riding in branches or tall weeds, small sticks or stems can slide under the mount and pop the screen off the bike. Keep an eye on the screen if you are riding in tall brush or weeds, or take it off and put it in your bike pack or pocket.
Wired and Wireless
There are two types of bike computers -- wired and wireless. On wired odometers, the wire runs up the bike's fork to the handlebars where it attaches to the display mount. Although some people prefer the stability of hard-wired odometers, the wire can become brittle and break off. This usually happens at the point where the wire enters the mount. Another problem with wiring is slack wire getting caught on branches, clothing or other bikes. Bike odometer wiring should always be secured by tape, zip-ties or simply wrapped around handlebars or forks -- not too tight -- but just tight enough to prevent loops and slack areas that can catch and tear the wire loose.
Wireless computers work by transferring the data through the air just like other wireless equipment. Problems with wireless odometers include loss of data, similar to a dropped call on a cell phone. Some cyclists prefer hard-wired odometers and will deal with the wire problems. Others like the freedom of wireless and will deal with the dropping of data.
Most bike odometers will adapt to almost any bike, and most have a built-in formula for each size of wheel, depending on the bike. When you place the computer on a bike, you enter a code into the computer telling it which size wheel to use. The computer uses the correct formula for that wheel to get the data right. If you enter the code wrong, the data will be wrong and the mileage will be off. You might not notice it at first, but even a slight deviation in wheel size will cause problems with distance traveled. Some bike computers come coded for a specific wheel, while others do not. If your computer doesn't match other bikes or mileage that you have measured when traveling in a car, your code might be off. The codes are always printed in the owner's manual for the odometer. Check it. If it's off, re-enter the code for accurate miles traveled.
Bike computers rely on batteries to operate. These batteries are very reliable and will last for many years. But if your screen begins to fade or you can't read it in bright sunlight, your batteries may need to be changed. It's a simple procedure that can make a big difference. The problem with this, however, is that stored data are often lost and your odometer defaults back to zero, causing you to lose your accumulated mileage. There are computers that store these kinds of data when you change batteries; if this is important to you, make sure to purchase one that stores the data. If your computer doesn't have this feature, make sure to write down the mileage when you reset the odometer with a new battery so you know how far your bike has traveled over the years