manual v. automatic transmission

A car’s transmission converts the rotational energy generated by the engine to an appropriate speed and torque, and transmits this energy to the driven wheels. In a vehicle with a manual transmission, the engine is coupled to the transmission with a clutch, and a lever is used to select different gear ratios. In an automatic transmission car, a fluid coupling called a torque converter connects the engine to the transmission. An intricate system of planetary gears, clutches, bands, and hydraulics automatically changes gear ratios based on factors including engine speed, vehicle speed, and load.

• Smoothly changing gears at the correct time on a manual transmission car takes practice and skill. An automatic transmission handles gear changes without the driver’s intervention.
• Manual transmission cars require the driver to make more decisions and movements, operating three pedals with both feet, and often taking one hand off the steering wheel to change gears. Automatics are substantially easier to operate.
• Because the driver selects the gear ratio, manual transmissions offer a greater degree of control, which can be useful for aggressive maneuvers, or when driving on slippery surfaces.
• Manual transmission cars have a clutch pedal, which automatic vehicles lack.
• Manuals have a gear lever that is moved up, down, left, and right to select gears. Automatics have a gear selector mounted on the steering column or the floor that can only be moved up or down.
• Manuals can be parked by placing the transmission in first gear (or reverse) and/or by engaging the hand brake (also called the parking brake). Automatics can be parked by selecting the ‘Park’ position on the gear selector, and/or by engaging the parking brake.
• Automatic transmissions can shift between gears much faster than a human can execute a manual gear change, during which time the engine is not delivering power to the wheels.
• Manual transmissions have fewer moving parts, and are cheaper to purchase, maintain, and repair.
• The clutch on a manual transmission rigidly links the engine to the transmission when completely engaged; an automatic transmission’s torque converter can slip somewhat.
• Manual transmissions can offer slightly better fuel economy than automatic transmissions.
• Manual transmissions weigh less than automatic transmissions.
• Manual transmissions typically have five or six gear ratios; automatic transmissions are commonly produced with four or five speeds.
• When the driver steps off the throttle in a manual transmission car, it slows down. This is not the case with an automatic transmission. Consequently, the brakes are used more and wear more quickly on automatic transmission cars.
• It’s easier for an inexperienced driver to damage the engine or transmission in cars with manual transmissions.
• Automatics require active cooling; manuals don’t.
• A vehicle with a manual transmission and a dead starter can be push started; automatic transmission vehicles can’t.

Cutaway view of a Lexus 8 speed automatic transmission.

Wikipedia on the benefits and drawbacks of manual transmissions