A bicycle designer uses maths to work out the frame angles, and the gearing. The number of teeth on the chainwheels, sprockets (cassette), chain length, and so on, all depend on maths.

If you are talking about a kind of human-powered, pedal-driven bicycle, it's a bicycle made first and foremost to be able to be ridden fast on good roads. Drop bar handlebars, skinny, high pressure tires, high gearing.

An example of simple gears is the chain, chain-wheel and free-wheel sprocket as used on a single geared bicycle. More complicated gearing is the modern bicycle's derailleur system of multiply chain-wheels, a cluster of sprockets, a chain, and gear changer mechanism.

What is gearing up in cars?

The top speed for a bicycle depends on the rider (strength, stamina, coordination, muscle speed), the gearing of the bicycle, and the terrain it is being ridden over. The current record speed is 268.831 km/h - which was set on a specially designed bicycle ridden behind a dragster (to eliminate most of the air drag) on October 3, 1995 on the Bonneville Salt Flats in Utah, USA.