Chassis Dynamometers
Chassis dynamometers measure an engine's torque output at the wheels of an automobile. The auto is placed on rollers, on which the tires turn, and the result is then measured. Some chassis dynamometers also work by attaching directly to the wheel hub and measuring its rotation. Chassis dynamometers may be fixed or portable units.
The horsepower measured by a chassis dynamometer is often 15 to 20 percent lower than results from an engine dynamometer, as friction and losses occur through various drivetrain components such as the gearbox or transmission. As a result, the measurements provided by chassis dynamometers are often less accurate and repeatable than those of engine dynamometers.
Chassis dynamometers are used for a number of testing purposes. For instance, semi-truck owners and owner-operators may use chassis dynamometer services to troubleshoot potential problems with their engines.