Wheel chocks can help to increase safety by keeping trailers, cars, and aircraft from moving when parked in a stationary position. Wheel Chocks are placed for safety in addition to setting the brakes. The bottom surface is sometimes coated in rubber to enhance grip with the ground. For ease of removal, a rope may be tied to the chock or a set of two chocks. One edge of the wedge has a concave profile to contour to the wheel and increase the force necessary to overrun the chock. Most commonly, chocks are seen on aircraft and train cars.
To use, wheel chocks must be selected to match the size of the tires on the vehicle and used in pairs, as the size of the tire is designed to be proportional to the vehicle’s weight and size.
Chock height required = Grade × the diameter of the wheel. For example if the grade is 20% then the chock required is 20% the height of the wheel so long as the chock can support the mass of the wheel. For cable drums that only sit on grades of 5% or less than the chock height would only need to be 5% of the height of the cable drum. For vehicles a chock between 20% and 25% of the height of the wheel should be used.