Forces & Towing

Towing a caravan or trailer affects the steering, acceleration and braking of a vehicle.

The term ‘acceleration’ is used here with the everyday meaning, i.e. speeding up.

When accelerating, there is more mass to be accelerated, so the maximum acceleration is reduced. The force that accelerates the towed vehicle is transmitted through the tow bar, which is in tension. As well as pulling forwards on the towed vehicle, the tow bar also pulls backwards on the car, reducing the resultant force that causes acceleration.

Tension in the tow bar is maintained when the car and towed vehicle are travelling at a steady speed, but now the force is reduced, being equal to the resistive force acting on the towed vehicle.

During braking, the car pushes back on the vehicle being towed, which in turn pushes forwards on the car. This reduces the car’s deceleration, so braking distances are increased. The diagram shows the forces in the tow bar when the car and vehicle being towed are accelerating and braking.