Belt final drive

A belt final drive does the same job as a chain, linking a front pulley on the gearbox or motor to a large pulley on the rear wheel, but with a toothed belt instead of metal links. The belt is a flat rubber band with moulded teeth on the inside face that mesh with teeth on both pulleys, so, unlike a V-belt, it cannot slip. Inside the rubber run cords of carbon fibre or aramid that carry the pull and keep the belt from stretching.

• The front pulley turns, its teeth push on the belt teeth, and the belt turns the rear pulley.
• The reduction is set by the pulley tooth counts, just as with sprockets.
• The belt is tensioned once at the axle adjusters and then largely left alone; because the cords do not stretch, it holds its tension for tens of thousands of kilometres.
• Nothing needs oil. A rinse with water and an occasional check for cuts or embedded stones is the whole service routine.

Belts are wider than chains and need a clean, straight run, so they appear where there is room and the rider values quiet: Harley-Davidson's cruisers and touring bikes, and electric scooters such as the Ather 450 series, whose mid-mounted motor drives the rear wheel through a belt. Many hub-motor scooters have no final drive at all.

What you notice: silence and smoothness, no oily rear wheel and no adjustment chores. The trade-offs are that a belt cannot be shortened or joined by the roadside, a stone trapped between belt and pulley can cut it, and changing the gearing means new pulleys, not a cheap sprocket.