Bicycle gearing

A modern racing bicycles is often equipped with a double-chainring crankset at the front and a 9-speed or 10-speed cassette at the back. Since wheel size is standardized, the gearing system is often described by stating the number of teeth in the chainrings and cogs. For example, the front chainring gearing is denoted "53/39", meaning that it has 53- and 39-tooth chainrings on the crankset. The rear cassette is denoted by its smallest and its largest. For example, a "12-25" means that the smallest has 12 teeth, and the largest has 25 teeth. Nowadays 9- and 10-speed cassettes are commonplace, which make the choice of intermediate gears less important than when there were only 5 cogs available in a cassette. These cassettes typically have a 7% step on the top 6 or 7 gears, and an 11% step on the lower gears.