The Complete Handbook of Vehicle Wheel Chocks

Chapter 1: Understanding Vehicle Wheel Chocks

Consider a loaded tractor-trailer. It can weigh upwards of 36,000 kilograms on the trailer axles, sitting on a few square centimeters of tire contact patch. If that trailer is disconnected from the tractor on an incline and not parked, the force resisting its movement is only the static friction of the brakes. If those brakes fail, or are inadvertently released, you have an 80,000-pound projectile moving in an uncontrolled direction. A wheel chock is the backup system that prevents that from happening. It is a mechanical wedge, placed against a tire, that provides an immovable barrier to stop wheel rotation and subsequent vehicle motion. While its function is simple, its design, selection, and application bear the weight of major safety compliance and accident prevention.

A wheel chock works by physically blocking the wheel. When a vehicle begins to roll, the tire rotates and tries to climb over whatever is in front of it. The chock presents a wedge with a specific angle and height. As the tire presses against the chock, the force from the vehicle is transferred down through the chock's body and into the ground. The chock essentially converts the rotational motion of the tire into a vertical force that presses down into the pavement, where friction holds it in place.

For a chock to function, three conditions must be met. First, the chock must be in firm, continuous contact with the tire. The shape of the chock's face must match the