How do I drive safely in heavy rain, and what is aquaplaning?
What tread depth is really doing in the wet, the warning signs that the tyres are about to lose contact with the road, and the one response that works when they do.
- Difficulty
- beginner
- Time
- 12 min
- Read
- 4 min
- Safety
- warning
Short answer
Aquaplaning is the tyre riding on a film of water instead of the road, and the sensation is the steering going suddenly light while the engine note rises. Do not brake and do not turn — ease off the accelerator, hold the wheel straight and wait for the tyres to bite again. Prevention is tread depth, correct pressures and slowing down, in that order.
A tyre in the wet is not gripping the road so much as clearing a path to it. The tread pattern's job is to pump water out from under the contact patch fast enough that rubber can touch tarmac, and there is a rate above which it simply cannot. That rate depends on how much water is on the road, how fast you are going, how much tread depth you have left, and how hard the tyre is pressed down. When it is exceeded, the tyre floats. Everything about wet driving follows from that one mechanism.
Safety
Step by step
- Slow down before the standing water, not in it.Speed is the variable you control moment to moment, and it has the largest effect on whether a tyre can clear the water. Ease off early rather than braking as you reach a puddle.
- Check tread depth honestly.The legal minimum in Great Britain is 1.6 mm across the central three-quarters of the tread, but wet performance falls off well before that. Aquaplaning resistance and wet braking both deteriorate markedly below around 3 mm, which is why many drivers replace tyres well above the legal limit.
- Keep pressures correct.An underinflated tyre flexes and its contact patch changes shape, which reduces how effectively the tread channels can evacuate water. This is one of the ways an unchecked tyre pressure becomes a wet-road handling problem.
- Recognise the warning signs.The steering goes light and vague, the engine note rises slightly as the wheels speed up with less resistance, and road noise changes. Some drivers describe it as the car feeling like it is floating, which is exactly what is happening.
- Do the one right thing if it happens.Ease off the accelerator smoothly. Do not brake, do not accelerate, and hold the steering wheel where it is. If the wheels are pointing straight, the car will settle straight when grip returns. If you have turned the wheel while floating, grip returns with the wheels pointing somewhere you did not intend.
- Leave a much bigger gap.Two seconds is the dry rule and four seconds is the sensible wet one. It also keeps you out of the spray from the vehicle ahead, which is a visibility problem in its own right.
- Avoid the ruts.Water collects in the wheel tracks worn into an old road surface, and driving slightly off them where it is safe to do so genuinely reduces the depth you are driving through.
- Use headlights, and know the wiper rule.Rule 226 requires headlights when visibility is seriously reduced, and heavy rain qualifies. As a working rule, if the wipers are on continuously, the headlights should be on too.
Common mistakes
- Braking when the car starts to aquaplane — Braking with no grip either does nothing or locks a wheel, and when grip returns it returns unevenly. Easing off is the whole technique.
- Trusting cruise control in heavy rain — Cruise control holds speed by adding power, which is the last thing you want when a tyre is starting to lose contact. Switch it off when it is genuinely wet.
If it doesn't work
Steering suddenly feels light on a motorway in rain
Cause: Partial aquaplaning — Fix: Ease off, hold the wheel straight, and slow down once grip returns. Then check tread depth and pressures at the next stop, because it means you are close to the limit.
Car pulls sideways when hitting a puddle
Cause: One side aquaplaning or dragging in deeper water — Fix: Hold the wheel firmly and ease off. This is a strong argument for slowing before puddles rather than after.
Windows misting up badly in the rain
Cause: Damp clothes and passengers, plus cold glass — Fix: Air conditioning with the demister, and avoid recirculation. Wet coats and a full car put a lot of moisture into the air.
Wipers judder or smear
Cause: Worn blades, or a screen contaminated with traffic film — Fix: Replace blades — they are cheap and are a genuine safety item. Clean the glass properly with a screen cleaner, because polish and traffic film cause more smearing than the blades do.
Spray from lorries blinding you
Cause: Following too close in the spray zone — Fix: Drop back further than feels necessary, or pass decisively when it is safe. Sitting in spray is one of the most under-rated risks on a wet motorway.
Questions people ask
Do stopping distances really double in the wet?
The Highway Code's typical stopping distances are stated for a dry road, and it notes that they can be at least doubled on a wet one. On ice it is far worse again. The practical consequence is the gap you leave, which is the only part of it you control.
Does ABS prevent aquaplaning?
No. ABS stops a wheel locking under braking; it cannot create grip that is not there. On a fully aquaplaning tyre there is nothing for the brake to act against.
Are wider tyres worse in the rain?
All else being equal, a wider tyre has more water to clear across its width, so it can be marginally more prone. In practice tread pattern, compound and depth matter far more than width, and fitting the size the car was designed for is the right answer.