Gears are used to increase the force or speed and gear ratio is a unit of bike gearing. To calculate the gear ratio, divide the number of teeth on the front chainring by the number of teeth in a rear sprocket: gear ratio = (number of teeth in front chainring) / (number of teeth in rear sprocket)

So, one revolution of the pedals at a gear ratio of 39/28 will take you 3.23 meters (2.31 x 1.4). If you multiply this figure by your cadence – let’s say 100 rpm in this case – you can calculate the speed. In this example, the bike would be traveling at 19.4 km/h (3.23 m x 100 rpm x 60 minutes).