What a bike computer actually does
A bike computer is a small display, usually fixed to the handlebar or stem, that shows numbers about your ride. At its simplest it shows current speed, distance travelled and elapsed time. More capable units add average speed, cadence, heart rate, elevation, a recorded map of where you went, and turn-by-turn directions.
The numbers are only useful if they change what you do. Speed and distance help you judge how far you have gone. Time helps you decide when to turn back. Cadence and heart rate help you pace yourself. None of them is a reason to take your attention off the road.
Two ways a computer gets its data
Basic units rely on a sensor attached to the bike. A small magnet on a wheel spoke passes a sensor on the fork, and the computer counts wheel turns. If it knows the wheel size, it can work out speed and distance. These units are simple, light and often have long battery life, but they only know what the sensor tells them.
GPS units work out position from satellite signals, so they can record a track and show a map without a wheel sensor. Many units can do both, and many also pair wirelessly with extra sensors for cadence or heart rate. Connection standards vary by brand, so check that a sensor and a computer say they support the same one before buying. The pages on riding with a GPS device and on a bike computer with GPS go into those units in more detail.
Setting it up before you ride
Do the fiddly part at home, not at the roadside.
- Charge or check the battery.
- Enter the wheel size if the unit asks for it, using the manufacturer’s instructions. A wrong setting makes speed and distance wrong.
- Choose which numbers appear on the main screen. Two to four large fields are usually easier to read at a glance than a crowded page.
- Pair any sensors and confirm that they show a reading.
- Check that the mount is tight and the unit does not rattle or swing.
If a sensor magnet or mount needs adjusting, follow the manufacturer’s guide, and ask a bike shop if you are unsure. Mounts and sensors can affect how a bike feels or sounds, and a loose part is an annoyance at best.
Mounting it where a glance is enough
The best position is one where you can see the screen with a very small movement of your eyes, without dropping your head. Many riders place the unit just in front of the stem or slightly above the bars, so it sits near the line of sight to the road.
Some practical points:
- Keep it clear of brake and gear cables, and make sure turning the bars to full lock does not snag anything.
- Avoid a position where your knee or a handlebar bag can hit it.
- Tilt the screen slightly toward you to reduce glare from the sun.
- Check the screen is readable in your usual light, including bright sun.
Bike lights, a bell or a phone mount may want the same bar space, so lay everything out before tightening anything. Lighting matters if you ride in low light, as the article on riding after dark explains.
Keeping your eyes on the road
A bike computer is a tool for the stretches where nothing is happening, not for busy moments. A few habits help.
- Glance, do not stare. A look that takes a moment is fine on a quiet, straight section. Anything longer should wait for a stop.
- Look up first. Before checking the screen, scan ahead, then look down briefly, then scan again. Good reading the road habits do not switch off just because a number is changing.
- Change settings only when stopped. Scrolling pages, changing a route or starting a workout while moving is a common way to drift or miss a hazard.
- Silence what you do not need. Alerts for every lap or zone can become a distraction. Turn off notifications you will not act on.
- In traffic, in a group or on rough ground, ignore the screen entirely. Keeping a steady line and watching what is around you matters more than any reading.
If you notice you are chasing the numbers rather than watching the road, that is a sign to simplify the display.
Reading the numbers sensibly
Treat the data as rough guidance. Speed varies with wind, hills and surface, so a lower number on a windy day does not mean you rode worse. Average speed is better for comparing similar rides than a single peak reading. Distance from a wheel sensor depends on the wheel size setting, while GPS distance can vary slightly with signal quality, for example under trees or between tall buildings.
Cadence, the number of pedal turns per minute, links to how you use your gears. The article on pedalling cadence explains the idea, and a cadence sensor is the usual way to measure it. Heart rate shows how hard your body is working, though it is affected by heat, tiredness, caffeine and many other things. If you have a health condition, or any concern about exercise and your heart, speak to a doctor before using numbers to push harder.
Looking after it
Wipe the screen and mount after wet rides, and keep the unit charged. Check the mount now and then as part of your regular pre-ride bike check, because vibration can loosen bolts and straps. Remember that a computer is also a theft target; many riders take it off when they lock the bike, and a locked bike is safer with a visible gadget removed.
Start simple: speed, time and distance. Add one measure at a time, and only keep the ones that help you ride more calmly and steadily.