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A cyclocomputer is a device mounted on a bicycle that calculates and displays trip information, similar to the instruments in the dashboard of a car. The computer with display, or head unit, usually is attached to the handlebar for easy viewing.

Contents 1 Basic operation 1.1 The head 1.2 The sensor 1.3 Transmission 2 Calibration 3 Additional information 3.1 Gearing 3.2 Performance 3.3 Environment

A basic cyclocomputer may display the current speed, maximum speed, trip distance, trip time, total distance traveled, and the current time. More advanced models also may display altitude, incline (inclinometer), and temperature as well as offer additional functions such as average speed, pedaling cadence, and a stopwatch. They have become useful accessories in bicycling as a sport and as a recreational activity.

A magnet is attached to a spoke of either the front or rear wheel. A Hall effect sensor is attached to the fork or the rear of the frame. The sensor detects when the magnet passes once per rotation of the wheel. Alternatively, a sensor may be attached to the wheel hub. Distance is determined by counting the number of rotations, which translates into the number of wheel circumferences passed. Speed is calculated from distance against lapsed time period. To measure cadence, a magnet is mounted to the crankarm, and a sensor mounted to the frame.

Some models use a wired connection between the sensor and the head unit. Other cyclocomputers, e.g. used by competitive cyclists, transmit the data wirelessly from the sensor/transmitter to the head unit.

Once a new computer is installed, it usually requires proper configuration. This normally includes selecting distance units (kilometers vs. miles) and the circumference of the wheel. Since the sensor measures wheel rotation, different wheel sizes will equate to different measures of speed and distance.

Besides variables calculated from the rotating wheels or crank, cyclocomputers can display other information

For integrated shifters on racing bicycles, the gear can be read by the computer: Shimano's Flight Deck and Campagnolo's ErgoBrain work with their respective systems to detect the gearing. This allows indirect measurement of cadence. These systems do not have sensors on the crankset or cassette to determine what gear the bicycle is in. They work exclusively with the shifters, which may result in misleading information. Instead of knowing what gear the bicycle is in, they rely on sensing when the cyclist changes gears using sensors in the shifters. If the gear change doesn't actually happen, or the computer's sensors are too sensitive (eg: when braking with STI-style shifters), the information displayed is not accurate.

With additional sensors, other performance measurements are available:

• A heart rate monitor can be integrated into the computer, using a chest strap sensor.
• A power meter measures power output in watts, using a torque sensor in the bottom bracket or rear hub.

Some models also have sensors built right into the head that measure and display environmental parameters such as temperature and altitude.