What is a Gearbox / Transmission?
Lets the engine spin at its happy speed no matter how fast the bike is actually travelling.
Simplified animation — not to scale.
In plain English
Inside the gearbox, sets of gears of different sizes let you trade engine speed for road speed — low gears for pulling away and hills, tall gears for cruising efficiently.
“Like a bicycle's gears, but shifted with your foot instead of your hand, and doing far more work.”
How it works
Each gear ratio pairs a different-sized gear on the input shaft with one on the output shaft. Moving the gear lever slides a selector drum that engages the chosen pair, while the clutch briefly interrupts drive so the swap happens smoothly. The output shaft then drives the final drive, chain, belt or shaft, to the rear wheel.
Signs of trouble
- ⚠Gears feeling notchy, hard to select, or false-neutrals appearing
- ⚠Gear popping back out under load
- ⚠Grinding noise on gear changes
- ⚠Unusual noise in a specific gear
£200–£1,200
Always get a written quote. Prices vary by bike, region, and parts brand.