Aquaplaning, also called hydroplaning, happens when a layer of water builds between the road surface and your tyres (RAC). With water instead of rubber on the road, the tyres can't grip, so steering and braking stop responding the way you expect. The Highway Code puts it simply: "if the steering becomes unresponsive, it probably means that water is preventing the tyres from gripping the road. Ease off the accelerator and slow down gradually" (Highway Code, rule 227).
Three things decide how likely it is: how much water is on the road, how fast you're going and how well your tyres can clear the water, which comes down to tread depth and pressure. This guide covers what aquaplaning feels like, exactly what to do if it happens, how tread depth and speed change the risk, and how to prevent it.
What is aquaplaning?
Aquaplaning is a loss of grip caused by water that your tyres can't clear quickly enough. A tyre's tread grooves channel water away from the patch of rubber touching the road. The RAC notes that "in heavy rain, each tyre can shift one gallon of water every second" (RAC). When there's more water than the tread can move, or the tyre reaches it too fast to clear it, the water builds up in front of the tyre and lifts it off the surface.
Continental lists the main factors as speed, tread depth, tyre pressure, the amount of standing water and the road surface (Continental). You control the first three. The fourth is why the classic danger spots are ruts, dips, lane edges and poorly drained stretches after heavy rain.
Aquaplaning can affect the front tyres, the rear tyres or all four. When the front tyres lose grip, the steering goes light. When the rear tyres lose grip, the back of the car can feel loose or start to slide.
Signs you're aquaplaning
The first sign is usually steering that suddenly feels light, as if the wheel has come loose from the road. The RAC and Continental describe these warning signs (RAC, Continental):
- Light or unresponsive steering. Turning the wheel changes little.
- Engine revs rising without the car speeding up, a feeling the RAC compares to dropping a gear at speed.
- A louder engine note or a rushing water noise from under the car.
- The back of the car drifting or starting to fishtail.
- The traction control warning flashing on the dashboard.
What to do if you aquaplane
Ease off the accelerator, keep the steering straight and don't brake hard. Let the tyres regain grip, then slow down gently. Step by step:
- Don't panic, and don't brake hard. The RAC advises resisting braking or hard acceleration. Continental says to brake only if a collision is about to happen.
- Take your foot off the accelerator gently. This is the Highway Code's instruction in rule 227: "ease off the accelerator and slow down gradually".
- Hold the steering straight. Michelin's advice is to keep the steering wheel as straight as possible and let the car cross the water. Sharp steering while the tyres have no grip can send the car off line when grip returns.
- Turn off cruise control if it's on, so the car isn't adding power (RAC).
- In a manual car, press the clutch to take drive away from the wheels, as Continental suggests.
- When you feel grip return, brake gently to lose speed, then carry on more slowly (RAC).
Once you're safely through, slow down for the conditions. If the car has gone through deep water rather than surface water, the Highway Code says your brakes may be less effective: "Test them at the first safe opportunity by pushing gently on the brake pedal to make sure that they work" (Highway Code, rule 121).
How tread depth affects aquaplaning
The less tread a tyre has, the less water it can clear, so the risk of aquaplaning rises as the tread wears. TyreSafe says that "the risk of aquaplaning increases as a tyre's tread depth is reduced as there is insufficient tread to clear the water properly", and cites testing by MIRA which found that "cars with 1.6mm tread had up to 44% longer braking distances in the wet than those with 3mm" (TyreSafe).
| Tread depth | What it means | Source |
|---|---|---|
| 7mm to 9mm | Typical tread depth of a new tyre | TyreSafe |
| 3mm | The minimum commonly advised by tyre and safety experts | TyreSafe |
| 2mm | TyreSafe says the tyre should be replaced by this point | TyreSafe |
| 1.6mm | Legal minimum for cars, "across the central three-quarters of the breadth of the tread and around the entire circumference" | Highway Code |
| Below 1.6mm | Illegal, with fines and three penalty points possible per tyre | TyreSafe |
The gap between 3mm and 1.6mm is where drivers get caught out. The tyre is still legal, but it's clearing noticeably less water, right through autumn and winter when the roads are wettest. Check your tread with the 20p test, and see UK tread depth law for the legal detail.
How speed affects aquaplaning
Speed is the factor you control most directly: the faster you go, the less time each tyre has to clear the water in front of it. Continental lists speed first among the causes, because higher speeds leave tyres less time to disperse water, and the RAC says driving faster significantly increases the danger (Continental, RAC).
Speed also multiplies the consequences. The Highway Code says that "in wet weather, stopping distances will be at least double those required for stopping on dry roads" (rule 227), and rule 126 says the two-second gap to the vehicle in front "should be at least doubled on wet roads" (Highway Code, rule 126). A speed limit is a maximum, not a target, and in heavy rain or standing water the right speed is well below it.
There's no single speed at which a car starts to aquaplane. It depends on how deep the water is and on the condition and pressure of the tyres, which is why worn or soft tyres can lose grip at speeds that feel perfectly normal.
Does tyre pressure affect aquaplaning?
An under-inflated tyre is more likely to aquaplane, and a correctly inflated one is less likely to. Continental names under-inflation as a cause of aquaplaning (Continental), and TyreSafe lists "less likelihood of aquaplaning" among the benefits of a properly inflated tyre (TyreSafe).
- Check pressures at least once a month and before long journeys, as TyreSafe recommends, with the tyres cold.
- Use the car's own figure from the handbook, fuel filler flap or door sill, and the higher full-load figure when the car is loaded.
- Don't add or release air "for the rain". There's no wet-weather setting; the correct pressure is the car maker's figure.
If one tyre keeps losing pressure, find out why rather than topping it up. Our tyre pressure guide explains how to check and what under-inflated tyres do.
How to prevent aquaplaning
Prevent aquaplaning by keeping good tread and correct pressures, and by slowing down when there's water on the road. The advice from Michelin, the RAC and Continental comes down to these habits:
- Replace tyres before they're worn out. Don't wait for 1.6mm; 3mm is the minimum commonly advised.
- Keep pressures right and check them monthly.
- Slow down in heavy rain and when you see standing water ahead.
- Leave a bigger gap, at least double your dry-road gap, as rule 126 advises.
- Turn off cruise control in the wet so you control the speed yourself (Michelin).
- Look well ahead for puddles and standing water, and avoid them where it's safe to do so.
- Steer, brake and accelerate smoothly. Sudden inputs are what turn a brief loss of grip into a slide.
- Compare wet grip when buying tyres. The wet grip grade on the tyre label is a like-for-like comparison between tyres; see the tyre label explained .
Standing water and floods
If you can't tell how deep water on the road is, don't drive into it. Aquaplaning is the main risk in shallow surface water at speed. Deeper water brings other dangers, including water getting into the engine and hidden potholes or kerbs.
- Slow right down before a sheet of water and keep the steering straight as you cross it.
- Don't assume it's safe because another car got through. A taller vehicle tells you nothing about your car's clearance.
- Test your brakes gently afterwards, as Highway Code rule 121 advises.
- Check your tyres and wheels once you're parked. Water can hide kerbs and potholes, and damage may only show up as a slow leak or a bulge later.
Before a journey in very wet weather, you can check for flood warnings on GOV.UK.
Worried about your tyres in the wet?
If your tread is getting low heading into the wettest months, replace the tyres before they reach the legal limit. Rescue Tyres is a mobile tyre service working from one base at Brent Cross, NW2; London and the Home Counties are closest, and for anywhere further out we tell you on the call whether we can take the job. We fit budget, mid-range and premium tyres, including all-season tyres, at your home, your workplace or a safe place off the road, sourced to your car's size, with the tyre label grades available so you can compare wet grip.
The price is confirmed on the call before any work, and a realistic arrival time is agreed on the call. We also work evenings, nights and weekends when the diary allows, at the same price as a weekday job. Call or WhatsApp 07473 720871, see mobile tyre fitting, or book online.
Sources
- GOV.UK Highway Code, Rules 226 to 237: driving in adverse weather conditions
- GOV.UK Highway Code, Rules 103 to 158, including rules 121 and 126
- GOV.UK Highway Code, Annex 6: vehicle maintenance, safety and security
- RAC, Understanding aquaplaning
- RAC, Checking tyre tread
- TyreSafe, Tread depth
- TyreSafe, The checks
- TyreSafe, Tyre pressure
- Continental, Aquaplaning
- Michelin, Aquaplaning
