Aquaplaning, also called hydroplaning, is one of the most unnerving things that can happen in heavy rain. It is when a tyre rides up on a film of water and loses contact with the road, taking grip, steering and braking with it until the tyre meets the surface again.
What happens
A tyre's tread grooves work hard in the wet, channelling water out from under the contact patch so the rubber can still touch the road. When water arrives faster than the tread can clear it, a wedge of water builds up at the front of the tyre and lifts it clear of the surface. At that point the tyre is effectively skating on water: the steering goes light and vague, and braking has little effect, because there is no firm contact to work against.
What raises the risk
Three factors dominate:
- Speed. The faster the car, the less time the tread has to clear the water. Speed is the single biggest factor, and the one most within the driver's control.
- Water depth. Standing water and heavy downpours overwhelm the tread far sooner than a damp road.
- Tread depth. Worn tread clears much less water. A tyre near the 1.6mm limit aquaplanes far more readily than one with deep grooves, long before it is illegal.
Under-inflation adds to the risk by distorting the contact patch, so correct pressures matter here too.
How to recover
The instinct is to brake and steer, and both make it worse. The correct response is calm and gentle:
- Ease off the accelerator smoothly to let the car slow
- Do not brake hard: heavy braking on water invites a skid
- Keep the steering straight and avoid sudden inputs
- As the car slows, the tread regains contact and grip returns; carry on at a reduced speed
Holding still and letting speed bleed off is what brings the tyre back into contact with the road. Sharp movements while the tyre is floating are what turn aquaplaning into a loss of control.
How to prevent it
The defences are simple and all sit with the tyres and the driver: keep good tread depth, since it is the tread that clears the water; keep tyres at the correct pressure; and above all slow down in heavy rain and standing water, leaving a much larger gap to the car in front. A tyre's wet grip rating also reflects how well it resists losing grip in the wet, so a set with a strong rating is worth choosing when tyres are due, which is easy when you buy online, since the wet-grip grade is printed on each tyre's label at Tyres.co.uk.
Aquaplaning is a vivid reminder of how much rests on the tread, and why wet grip falls away as tyres wear, the same reason worn tyres take so much longer to stop in the rain.
From the workshop: the drivers who describe a scary "floating" moment in a downpour are almost always low on tread. Deep grooves move a startling amount of water. Once they are worn down, the tyre simply runs out of places to put it.
Sources and accuracy. The mechanism, risk factors and recovery advice here reflect motoring-authority guidance at the time of writing. This is safety-critical, so confirm the recovery advice against current official sources, and treat any handling emergency with caution. If anything here looks wrong, get in touch and we will check it and put it right.
Common questions
What is aquaplaning?+
Aquaplaning, or hydroplaning, is when a layer of water builds up between the tyre and the road faster than the tread can clear it. The tyre lifts onto the water and loses contact with the surface, so grip, steering and braking all fall away until the tyre regains the road.
What should I do if my car aquaplanes?+
Ease off the accelerator gently, keep the steering straight, and do not brake hard or make sudden steering movements. Let the car slow until the tyres bite again, then carry on at a reduced speed. Hard braking or steering while aquaplaning can turn a loss of grip into a skid.
What causes aquaplaning?+
Three things mainly: speed, water depth and tread depth. Higher speed gives the tread less time to clear water; deeper standing water overwhelms it; and worn tread clears far less water than new. Under-inflation and wide tyres can add to the risk. Heavy rain combines several of these at once.
Does tread depth affect aquaplaning?+
Strongly. The tread grooves are what channel water out from under the tyre, so the deeper the tread, the more water it can clear. As tread wears, water-clearing capacity drops sharply, which is why worn tyres aquaplane far more readily than new ones, well before the legal limit.