Aquaplaning
Riding on water rather than road, when the tyres cannot clear standing water fast enough.
A tyre works by pushing water out through its tread so the rubber can touch the road. Above a certain speed, in deep enough water, it cannot shift it quickly enough and a wedge of water lifts the tyre clear of the surface. At that point steering and braking do almost nothing, because nothing is in contact with the road.
The signs are a sudden lightness in the steering and the engine note rising as the wheels speed up. The response is to do nothing abrupt: ease off the accelerator, hold the wheel straight, and let the speed fall until the tread bites again. Braking or steering hard while aquaplaning is what turns it into a spin.
Worn tyres bring it on at far lower speeds, because tread depth is exactly the capacity to move water. This is the practical reason behind the minimum legal tread depth, rather than it being an arbitrary number.
8 practice questions on this
Each one shows the answer, and our note on why every other option is not it.
Lorry & Bus (LGV/PCV)
- You're driving in heavy rain. What should you do if your steering suddenly feels very light? The road
- What's the greatest risk to your safety when you're overtaking on a motorway in very wet weather? The road
- You're driving a large vehicle in heavy rain on a motorway. You slow down to reduce the risk of aquaplaning. For what other reason should you slow down? The road
Driving Instructor (ADI Part 1)
- Why should you teach your pupils to test their brakes after driving through a ford? Band 2 traffic signs and signals, car control, pedestrians, mechanical knowledge
- What happens if your vehicle starts to aquaplane? Band 2 traffic signs and signals, car control, pedestrians, mechanical knowledge
- You're driving in heavy rain. What should you do if your steering suddenly feels very light? Band 2 traffic signs and signals, car control, pedestrians, mechanical knowledge