Wheel chocks are defined as any wedge-shaped object placed in front or behind a tire to prevent the vehicle from rolling. The chocks are a safety item used whenever working on a vehicle or wherever there is concern of the vehicle rolling. Typical use of a chock is during maintenance that requires the vehicle to be raised on one end or when parking a larger vehicle on an incline. The exact size of chocks you may need depend upon your vehicle and your needs.
Measure the height of your tire. A wheel chock is best sized according to the size of the tire and should be approximately 1/4th the height of the tire. If your tire is 36 inches in height, your wheel chock should be around 9 inches high and fit snugly beneath the tire.
Look at the grade of the terrain the vehicle is to be placed upon. Grade refers to the angle of the ground. While a chock needs to be approximately 1/4th the height of the tire, you may require more than one chock. If you are on a 30 percent grade--which is approximately the angle of stairs, you will want your chocks to be sufficiently large enough to hold your vehicle while in neutral and you will want a minimum of two chocks.
Look at your owner's manual. For larger vehicles such as RVs and tractor-trailers, the vehicle's manual may describe a need to chock both the front and rear of the tires for reasons of potential brake failure. Even if you are parked on level ground, there is still danger of a vehicle rolling.
