Abstract: A roller dynamometer is provided, having at least one supporting carriage having a rotatable roller and a dynamometer linked to the roller for measuring torque output of a vehicle. The carriages are rollable on a substrate for positioning under a vehicle. In one aspect, multiple dynamometer and roller units are provided, for engagement with multiple vehicle wheels, with the units being linked electronically for common control by a control unit that simulates either straight line or curved driving conditions. In a further aspect, the dynamometer is supported on the carriage by a rotary mount. In a further aspect, the rollers have a generally hourglass shape to permit vehicle wheel self-centering.