The term dynamometer is commonly defined as – “an instrument for measuring mechanical force”, with force being commonly defined as – “any external agent that causes a change in the motion of a free body, or that causes stress in a fixed body”.

In the case of the chassis dynamometer, the purpose at hand is to measure the rotational force of the driven wheels mounted to the vehicle under test. This is typically achieved via a series of rollers - which when coupled to a vehicle’s tyres resembles a toothless gear arrangement. In many cases, an absorption device is incorporated into the roller arrangement so as to allow for “steady state” testing.

While an engine dynamometer measures the rotational force, or torque, of a prime mover output shaft, the chassis dynamometer measures the force that reaches the contact patch on the tires. Of course, the prime mover output will have been passed through the transfer case, the transmission, the axle, and finally through the wheel and tyre.