Wheel Chock
A wheel chock is a wedge-shaped safety element that prevents the vehicle from rolling back and forth while parked. The handbrake of a towed caravan holds only its own axle and is not considered sufficient on its own on sloping or slippery ground; on a motorhome, the park position alone is no guarantee either. Levelling jacks are under no circumstances a substitute for a chock.
A chock holds the vehicle in place by mechanically preventing the wheel from turning. Jacks, on the other hand, are designed to carry vertical load; their resistance to horizontal force depends only on the friction between them and the ground, and that friction falls quickly on slippery, wet or sloping ground.
- Width: the chock must be wider than the tyre width.
- Placement: placed both in front of and behind at least one wheel, on both sides of the vehicle.
- Order: chocks are placed before the jacks are lowered and removed after the jacks are retracted.
- Parking on a slope: the steeper the slope, the more important the chock becomes.
During levelling, part of the load on the wheels transfers to the jacks; even if the wheel keeps contact with the ground, the friction force decreases. This is the moment when the chock is needed most. Using the jacks in place of the parking brake or the chock creates the risk of the vehicle sliding off the jacks.
Context in which this term is used: Guide to automatic RV levelling