Tachometers, which measure the rpm, or revolutions per minute of a car's engine, provide useful information as to how fast and hard a car engine is working. What follows is a brief list of what tachometers measure and how they provide a window into a car's running engine.
A tachometer measures how many times a car's engine crankshaft spins, the part that is responsible for moving the engine pistons up and down in a car's engine cylinders. One crankshaft revolution is equal to one rpm (revolution per minute).
A tachometer compliments a speedometer, which measures the miles per hour that a car travels. As a rule, engine rpms increase as miles per hour increase, but rpm's are extremely volatile, with the ability to go up and down dramatically within seconds depending on how a car's engine is accelerated and/or revved up.
Tachometers are most useful in cars that have manual transmissions, which enable drivers great leeway in terms of how and when they shift the car's transmissions. To maximize fuel efficiency and engine performance, manual transmission vehicles should be shifted within certain rpm ranges; tachometers provide this information.
The faster an engine crankshaft spins, which translates into a faster-moving engine, the more stress and strain an engine experiences. All tachometers have orange and red zones on their dials, colors that represent engine work rate danger zones.
The faster a car engine spins, the more friction and heat get generated in the engine. Although tachometers don't directly measure an engine's operating temperature, they give a general idea as to how hot a car's engine is running.
