The transmission matches engine speed to road speed. An engine has a narrow power band. The wheels need to turn slowly for a start and quickly for a highway cruise. Gears bridge that gap.

Manual transmissions use a clutch and a lever. Automatic transmissions use a torque converter and planetary gearsets. Continuously variable transmissions use a belt and pulleys to provide infinite ratios. Dual-clutch transmissions use two clutches to shift without interrupting power. Each design trades off cost, efficiency, and driving feel.

Transmission types at a glance

• Manual: cheap, durable, driver-controlled.
• Torque-converter automatic: smooth, common, improving.
• CVT: efficient, drone-prone, popular in small cars.
• Dual-clutch: fast shifts, complex, performance-oriented.

The transmission is one of the most expensive components in a car. Fluid changes extend its life, especially on automatic and CVT units. Towing without a transmission cooler overheats the fluid and shortens life. A slipping transmission, delayed engagement, or shudder under acceleration all point to trouble. Rebuilding or replacing one can cost more than the car is worth, so maintenance is worth the effort.