The difference between a wheel-sensor unit and GPS
A basic bike computer counts wheel turns with a sensor and a magnet. It is simple, and it works anywhere because it needs no outside signal. It cannot tell you where you are, though, and it cannot save a map of your ride.
A computer with built-in GPS receives signals from satellites and uses them to estimate position several times a second. From that it works out speed, distance, and the path you took. Some GPS units also include a barometer to estimate climbing from changes in air pressure, which can be steadier than satellite height alone, but this depends on the model.
The sections below cover what changes in practice.
Recorded tracks
The most noticeable change is that the ride is recorded as a line on a map. After you finish, you can see the route you took, how far you went and how long each section took. Many people find this the best part: it makes it easy to repeat a good ride, share one with a friend, or work out where you took a wrong turn.
Things to know:
- The unit needs a moment to find satellites at the start. Wait for it before you roll.
- Accuracy dips between tall buildings, in tunnels and under dense tree cover, so the track can look jagged or cut corners.
- Distance may differ slightly from a wheel sensor. Neither is perfect, and a wheel sensor depends on the wheel size setting being correct.
- Saving a ride at the end is usually a button press. Check you have done it before you switch off.
Turn prompts and following a route
Many GPS computers can follow a loaded route and give a prompt before a turn, with a beep, a message or an arrow on the screen. Some show a simple line to follow, and others offer a full map. This can be a relief on unfamiliar roads, because you do not need to stop to check a phone.
A few sensible habits:
- Load and check the route before leaving, not at the roadside. Look for roads that suit your bike and confidence. The article on planning a route covers choosing sensible roads.
- Treat prompts as help, not orders. If a turn takes you onto a road that looks unsafe, a private way, or a path your bike is not suited to, stop somewhere safe and decide for yourself.
- If the unit offers a re-route option, use it when stopped rather than while moving.
- Keep glances brief. A short look at the next arrow is fine; reading a full map is a job for a stop.
The deeper subject of planning and following routes has its own article, so this one keeps to the basics of what the hardware does.
Battery use
GPS units use more power than a wheel-sensor unit because the receiver and a bright screen are working constantly. Battery life varies widely between models and is shown in the manufacturer’s specifications, but it is generally shorter in cold weather and when the backlight is bright or sensors are paired.
To get through a long ride:
- Charge fully the night before.
- Reduce screen brightness or the time the backlight stays on where you can.
- Switch off sensors and features you are not using.
- Carry a small battery pack and cable if your unit can charge on the move and you ride long distances.
- Know what you will do if the unit dies: a printed note of the route, a phone map or someone who knows your plan.
A wheel-sensor unit’s small battery often lasts a long time, so it makes a sound backup for tracking basic speed and distance.
Mounting and handling
Because GPS units are larger and often heavier than simple computers, a solid mount matters. Use the mount that comes with it or a well-made one made for your unit, tighten it according to the instructions and check it is secure before each ride. Put it where you can see it with a quick glance, away from cables and not where a knee could hit it. The pillar article on riding with a bike computer covers positioning.
Choosing between them
A wheel-sensor computer suits someone who only wants speed, distance and time and values low cost and long battery life. A GPS computer suits someone who wants maps, recorded rides and turn prompts, and who is happy to charge it regularly. Neither is better in every case. If you are unsure, start with the simpler option and upgrade when you know what you want to track.
Whichever you choose, the same rule applies: the screen is a helper. Your attention belongs on the road, particularly in traffic, junctions and rough surfaces.