The purpose of the transmission is to transfer the power generated by the engine to the drive axle and wheels by using different gears. A car’s engine rotates within a fixed range of speeds, generally from 600 to 7,000 revolutions per minute (rpm) for most passenger vehicles. The vehicle’s wheels typically spin from 0 to 1,800 rpms, so the transmission uses different gears with specific ratios to match the most efficient use of engine power for the vehicle’s speed.
For instance, when starting from a full stop, your car’s engine is spinning much faster than the wheels so a lower-ratio gear that supplies higher amounts of torque is needed. When traveling at highway speeds, the wheels may be turning much faster than the engine, meaning a higher-ratio, low-torque gear is needed.
There are a few varieties of transmission types found in most modern vehicles: