If the vehicle is towing a trailer (in British English a caravan) the weight distribution of the trailer is critical. If too much of the trailer's weight, called "tongue weight", presses down on the vehicle's tow hitch (more than 15 percent) it can cause the vehicle to go out of control. Too little tongue weight (less than 10 percent) can cause the trailer to sway from side to side. this in turn can make the vehicle difficult or even impossible to control. The shorter the wheelbase the more quickly these forces can cause a loss of control. A longer wheelbase vehicle is generally more desirable for towing. Each vehicle has a tow rating showing how much weight it can tow safely.