Which type of dyno consists only of rollers and does not use a power absorber?

• A. Eddy current
• B. Inertia
• C. Waterbrake
• D. Hydraulic

Answer: (B)

The key idea is measuring engine power by storing energy in a rotating mass rather than dissipating it with a brake. An inertia dynamometer uses only rollers to couple the engine to a heavy flywheel or inertial mass. The engine’s torque accelerates this inertia, so energy goes into increasing the flywheel’s kinetic energy rather than being absorbed as heat. By observing how quickly the inertia speeds up (or slows down when the engine isn’t supplying heat-dissipating loads), you can calculate the engine’s power from the torque and the rate of acceleration. This means there’s no distinct power absorber converting energy to heat or fluid resistance, which is why it’s the roller-only type.

In contrast, the other approaches rely on a brake or absorber (electromagnetic, water, or hydraulic) to dissipate the engine’s power as heat, providing a steady resisting load. That makes them different from the roller-and-inertia setup.