| Transmission Basics |
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The first cars didn’t have transmissions so they couldn’t go very fast. Today’s cars have as many as five gears; first gear is for starting and the last gear is for highway driving. Try starting a car out in fourth or fifth gear and you’ll appreciate the function of the transmission. Tech Tip The highest transmission gear for most cars is about 1:1 (one to one), meaning that every revolution of the engine’s crankshaft results in a revolution of the driving wheels. Here’s the gear ration for a newer Volkswagen Beetle:
Changing from one gear to another can be difficult without the clutch. A clutch is a simple device that engages and disengages the transmission from the engine to make the transition between gears smoother. For many years, all automotive transmissions required some guesswork by the driver. At what speed should the driver change from first to second or third to fourth? The majority of today’s cars use an automatic transmission that automatically changes gears as needed. The “clutch” for an automatic transmission is called a torque converter.
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A transmission transmits. That is, it takes the rotation power from the engine’s flywheel and sends it on its way toward the wheels. Sure, the engine’s rotation could be sent directly to the wheels, but a car’s speed would be limited to about 20 miles an hour. That’s not practical. So, just like gears on a 10-speed bicycle, the transmission uses the car’s momentum to change gears and extend the power available to the wheels.
