Truck

—The group of wheels and supporting framework containing the brakes, motors and driving gear of an electric railway car. There are two chief types of trucks: (a) the single truck having four wheels with a single motor on each axle, one only being used to support the car body; and (b) the double truck, each with four wheels of the same size, carrying a motor on each axle, two trucks being used per car. The maximum traction truck has two large, and two small wheels, so arranged that the weight will largely rest on the large wheels which are driven by the motor.