Transmission
This domain covers clutch operation, manual gearboxes, synchronisers, automatic transmissions, CVTs and the gear ratios that multiply engine torque. Questions often ask why a gearbox is needed, how a clutch releases drive, and how overall ratio affects road speed and tractive effort.
Core rules
A clutch transmits torque through friction between flywheel, disc and pressure plate; the release bearing acts on the diaphragm spring to unload the disc. Manual gearboxes use sliding hubs and baulk-ring synchronisers to equalise shaft speeds before engagement. A simple gear pair changes torque and speed inversely: a larger driven gear reduces speed and increases torque. Overall ratio equals gearbox ratio multiplied by final-drive ratio. Automatic transmissions use planetary gearsets, clutches and brakes; CVTs vary pulley diameter and belt contact radius.
Worked example
A car has first gear 3.40:1, final drive 4.10:1 and a tyre rolling radius of 0.30 m. Overall ratio is 3.40 x 4.10 = 13.94:1. At 3000 rpm engine speed, wheel speed is 3000 / 13.94 = 215 rpm. Road speed is 2 x pi x 0.30 x 215 x 60 / 1000 = 24.3 km/h. Wheel torque for 180 Nm engine torque is 180 x 13.94 = 2509 Nm, before losses.
Traps
Inverting the ratio when calculating speed; using tyre diameter instead of rolling radius; confusing clutch slip with a worn release bearing; and assuming an automatic transmission has no mechanical clutches.