How to set up a bike computer: wheel, sensors, and the first entry

FATRACING · Updated October 9, 2026

For a simple bike computer, first set the wheel circumference and units. For a GPS model, add sensors, bike profile, and recording order. Check the result with a short ride: numbers on the screen don't necessarily mean that the activity has been saved.

Magnetic computer or GPS

The magnetic system counts wheel rotations: the magnet passes near the sensor, and the computer multiplies the number of rotations by the given circumference. The sensor installation, gap, and magnet direction must follow the model's instructions.

The GPS computer can determine the speed by satellites and use a separate speed sensor. A modern sensor on a bushing often works without an external magnet. Check which source is active and whether manual wheel size is required.

Don't use button combinations from a similar model: a reset can delete records. First, find the manual for the exact model name on the case.

How to measure the circumference of a wheel

Pump the installed tire to the operating pressure.
On a level surface, mark the position of the nipple near the floor.
Roll the wheel exactly one revolution with normal load. An assistant can hold the bike and make a second mark.
Measure the distance between the marks, repeat the measurement and record the units.

Rolling measurement is described in Cateye Padrone Smart manual. It takes into account your tire and load better than the single designation '29 inches'.

Training result: 2.18 m is 2180 mm or 218 cm. Enter the value that the field of your model requires. If the field expects millimeters, the number 218 will be an error of ten times. This is an example of recalculation, not the circumference of all 700C wheels.

Where to specify size and units

In the manual, find wheel size or tire circumference. Some models offer a tire chart, others — the circumference number. For Cateye Padrone Smart, the input refers to the selected speed sensor: the setup procedure. Other devices can automatically calibrate the sensor using GPS.

Check kilometers or miles, time format, and the selected bicycle profile. With multiple sensors, the size should relate to the desired wheel. The outer diameter of the wheel and the rim diameter ETRTO are different parameters.

For rim and tire sizes, there is Wheel and tire tool. It helps with compatibility and wheel calculations, but does not replace rolling measurement for the computer.

How to check sensors

Wake up the sensor by rotating the wheel or pedals according to the instructions.
Connect it in the computer menu, check the identifier and purpose: speed, cadence, heart rate, or power.
Check that the data changes when your sensor moves, not the neighboring bicycle.
If there is no data, check the battery, installation, and protocol compatibility before resetting the device again.

A speed sensor does not have to show cadence: these are different measurements. On the first screen, leave the fields you need and check them before a long ride. The menu names and ANT+/Bluetooth capabilities are determined by the model.

GPS, route and trip recording

On the street, wait for the position to be determined according to the device's instructions. A loaded route and activity recording are different things: the presence of a line on the map does not prove that the computer is recording the ride.

Before going out, check the route, battery, and available fields. Press the designated start recording button, and after the ride, press the stop and save button. Export or sync the activity and open the result.

Route preparation is described in GPX guide, and the transfer of records is in the instructions Wahoo and COROS. Check the path of your model, and don't expect all manufacturers to have the same buttons.

If the speed or distance is incorrect

Consistent error in one direction: For the speed sensor, check the circumference, units, and profile. If the tutorial example enters 2100 mm instead of the measured 2180 mm, the distance will be approximately 3.7% less with a correct count of rotations.
The readings disappear: Check the battery, installation, and connection. For the magnetic system, separately check the gap and passage of the magnet according to the instructions.
GPS and sensor give different numbers: Check the active speed source and reception conditions. Do not change the circumference just to match a short section with weak GPS.

On a test ride, compare the duration and distance traveled, then open the saved record. Cateye instructions were checked on October 9, 2026. The numbers above are training calculations; readings from a real sensor were not measured within the article.