What is the best way to drive over speed cushions?

Q. What is the best way to drive over the split type of speed humps so as not to damage the suspension and tyres? GP, Bushey, Hertfordshire

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A. There are regulations covering the shape and size of speed bumps on public roads, although not humps on private land. The split type is called a speed cushion and is designed to enable fire engines and ambulances to drive with the wheels on either side of the hump to get to an emergency quickly or to transport an injured passenger smoothly.

Generally speed bumps on public roads are designed to slow traffic to about 20mph and as long as you take them at that speed, it doesn’t really matter how you approach them — no harm will come to your car. Some people think that if you straddle the cushion the sideways slope will put your wheel out of alignment, but the sideways forces involved are much less than any cornering stresses the suspension is designed to cope with. But if you do feel more comfortable driving one wheel over the top of the cushion with the other on the road, this too will do no harm — provided nothing is coming the other way, of course.

The very narrow rubber humps you find in car parks or on private land are a different matter and are not covered by the same legal regulations. These will shake the fillings out of your teeth at anything above walking pace because that’s the speed they’re designed to slow vehicles to.

Drive over them at a pedestrian pace and your suspension, wheels and tyres will not suffer. Hit one any faster, especially at an angle, and the wheel alignment could be upset, just as if you’d driven over a pothole.

TIM’LL FIX IT
Tim Shallcross used to train AA patrols to fix cars. Now he advises the Institute of Advanced Motoring – read more from Tim here.

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