There are a range of factors that can affect your cycling speed. Obviously fitness is one of them, however, weather conditions and the varying gradients of the road play a huge part too. The most advanced way of measuring how these factors affect your performance speed is with the aerodynamic Wireless Polar CS speed sensor.
Measures your current, average and maximum speeds
Track your average speed to see your progress and performance improve
Light yet tough, and easy to attach
Buy Polar CS500 Bike Mount and CS Speed Sensor Set from Chain Reaction Cycles, the world's largest online bicycle store.