When rear-leaf springs control axle windup during acceleration, this system is referred to as what?

The correct choice refers to a system known as the Hotchkiss drive, which incorporates traditional leaf spring designs that control axle movement during acceleration. In this type of system, the leaf springs are positioned longitudinally and are secured to the axle at one end while the other end is attached to the vehicle's frame.

When the vehicle accelerates, the torque generated by the engine causes the axle to attempt to rotate around its connection to the leaf springs. The design of the Hotchkiss drive effectively resists this rotational movement – commonly referred to as axle windup – allowing the vehicle to maintain better traction and stability. This is particularly important in rear-wheel drive applications, where managing forces transmitted through the suspension is crucial for performance.

Other systems listed, such as the trailing arm and semi-trailing arm, have different configurations and functions, primarily focused on lateral location stability rather than managing axle windup. The torque arm is designed to limit the axle's rotation, but it works more in conjunction with other types of suspensions rather than being the primary method of addressing axle windup in a leaf spring setup. Therefore, in the context of controlling axle windup specifically in a rear-leaf spring configuration, the Hotchkiss drive is the most accurate description.