Hydroplaning: what speed, which tyres, what to do

In short. Hydroplaning (called aquaplaning in Britain and Australia) happens when a tyre cannot push water out of its contact patch fast enough, so a wedge of water lifts the tread off the road and steering and braking almost disappear. NASA's classic formula puts the speed for a full lift-off at about 10.35 × √(tyre pressure in psi) mph, which gives 56 to 66 mph (90 to 106 km/h) at common car pressures, but Germany's ADAC measures new tyres starting to aquaplane at 75 to 85 km/h (47 to 53 mph) in 7 mm of water, and says the risk rises clearly from about 80 km/h (50 mph). Worn tread, low pressure, wide tyres and deep water all bring that speed down; if the steering goes light, lift off the accelerator, keep the wheel straight and let the car slow down.

What hydroplaning is, and when it occurs

Hydroplaning occurs when water on the road is deeper than the tread can clear at the speed you are driving. As the tyre rolls, water builds up in front of it; if it cannot escape through the grooves or out to the sides, it forms a wedge that pushes under the front of the contact patch. NASA's engineers described a tyre in that state as detached from the pavement, its ability to brake or corner "almost completely lost" (NASA TN D-2056, November 1963).

It is a matter of degree. Michelin UK defines it as the separation between the tyre and the road created by a layer of water, which builds up gradually as speed or the volume of water rises; most of the time only part of each tyre loses contact. Michelin puts road conditions with a risk of total aquaplaning at 0.01% of cases when driving in rain (Michelin UK). Partial aquaplaning is far more common, and it is enough to lengthen braking and make the steering vague.

Three things decide whether it happens:

• Water depth. NASA found that tyres will not hydroplane below a minimum depth, and that this depth varies with the tread and the road surface: from about 0.1 to 0.4 inch (2.5 to 10 mm). For a rib-tread car tyre on a concrete test runway it measured 0.2 to 0.3 inch (5 to 7.6 mm). Ruts, dips and poor drainage are where that depth is reached.
• Speed. The water's lifting force grows with the square of speed, which is why a car that is stable at 40 mph can float at 60.
• The tyre. Pressure, tread depth, tread pattern and the shape of the contact patch, covered below.

Hydroplaning speed: NASA's formula at real tyre pressures

In 1963 Walter Horne and Robert Dreher of NASA's Langley Research Center simplified their equation to Vp = 9 √p knots, or Vp = 10.35 √p statute miles per hour, with p the tyre inflation pressure in pounds per square inch. They noted that most American cars of the time ran 16 to 30 psi, which put total hydroplaning below the 60 to 70 mph speed limits, while trucks and buses at 50 to 90 psi were less exposed. Here is that formula applied to today's pressures (our calculation; 1 bar = 14.5038 psi):

Two things the table tells you. First, pressure matters, but through a square root: a tyre 20% under its pressure loses about 10.6% of its hydroplaning speed (1 − √0.8), and a tyre at 1.8 bar instead of 2.4 bar loses 13%. ADAC adds that both too much and too little pressure favour aquaplaning; the pressure to use is the car maker's, on the door pillar or in the handbook (tyre pressure guide).

Second, do not read these numbers as a safe limit. NASA says its formula assumes three things: the average bearing pressure under the tyre equals the inflation pressure, the fluid has the density of water, and the lift coefficient is about 0.7. It also says the speeds are valid for smooth or closed-pattern tyres, or for ribbed tyres when the water is deeper than the grooves, and that little data existed for shallower water. On real cars, ADAC's tests in 7 mm of water record aquaplaning speeds of about 75 to 85 km/h for tyres with their original tread of about 8 mm, and only narrow new tyres (155 mm) can go above 90 km/h (ADAC, 16 October 2025, in German). At 2.4 to 2.8 bar the formula says 98 to 106 km/h: in our comparison the measurement comes in roughly 15 to 30 km/h lower. ADAC's page does not say exactly which criterion it uses to call the onset, so the comparison is ours and approximate, but the direction is clear. ADAC also notes that puddles on real roads are often much deeper than 7 mm, and that a tyre braking at 100 km/h can aquaplane even on a road that is only damp when its tread is down to about 3 mm.

NASA also reported a hysteresis, measured on aircraft tyres: a tyre that had spun down on the water needed a ground speed up to 13 knots (15 mph) lower before it spun up again. Once you are floating, you have to slow down further than the speed at which it started.

Tread depth: what worn tyres change

The grooves are the escape route. Continental UK says new tyres can disperse up to 30 litres of water a second at 50 mph, and that this capacity falls as the tread wears. Its wet braking test at the Contidrom found stopping distances 2.2 metres longer at 3 mm of tread and 6.8 metres longer at the 1.6 mm legal minimum, against new tyres with 8 mm (Continental UK, aquaplaning). The page gives the extra distance but not the test speed.

The legal minimums are not the same everywhere, and none of them is set for aquaplaning:

So a tyre can be legal and still aquaplane at motorway speed in standing water. ADAC advises replacing worn summer tyres early, especially below 3.5 mm; the tread wear indicators, small bars moulded into the main grooves, show where 1.6 mm sits. Our guide to legal tread depth in the UK, US, Australia and Canada shows how to measure it.

Tyre width and bigger wheels

ADAC states it plainly: wide tyres tend to aquaplane more than narrow ones, because the wider the tyre, the more water it has to push aside and the longer the paths that water must travel; under otherwise equal conditions, wider tyres tend to have lower aquaplaning speeds. Continental UK lists wide, low-profile tyres among the factors that raise the risk.

NASA's formula cannot show this, because width is not in it: only pressure is. Our reading of why width still matters, as an illustration with invented numbers: NASA assumes the load on a tyre is carried at roughly the inflation pressure, so the contact area is close to load divided by pressure. With 400 kg on a wheel at 2.4 bar, that is 3,924 N / 240 kPa, about 164 cm². If a narrower tyre puts down a patch 150 mm wide, the patch is about 10.9 cm long; if a wider one puts down 200 mm, it is about 8.2 cm long. Same area, but the wider patch meets a broader front of water and has less length in which to channel it away through the grooves and out to the sides. Continental adds that lighter vehicles may aquaplane more easily because they press less on the tyres; NASA, for its part, found the vertical load had only a small effect on hydroplaning speed, because the footprint grows with the load. On weight, the two sources do not agree.

What a bigger wheel changes is usually the tyre that goes with it. Keeping the overall diameter the same on a larger rim means a lower sidewall, and an upsize often comes with a wider section. The wheel's diameter is not named as a factor by any source we read; the tyre's width and profile are. Our guides to tyre sizes for 19-inch wheels and reading a tyre size show what each figure on the sidewall means, and the tyre size calculator compares two sizes. Onyx Forged does not recommend a size or an offset: the sizes listed for your car are in its handbook and its registration documents.

The EU tyre label does not settle it either. Its wet grip class, A to E, comes from a wet grip index measured under UN Regulation No. 117, with A for a C1 car tyre at G ≥ 1.55 and E at G ≤ 1.09 (Regulation (EU) 2020/740, Annex I). The European Commission describes it as a proxy for braking distance on wet asphalt, worth 3 to 6 metres between classes (European Commission, tyres). It is a braking test on a wetted surface, not an aquaplaning test in standing water, and it is measured on new tyres.

How to avoid hydroplaning

1. Slow down in heavy rain and standing water. ADAC suggests a speed well below 80 km/h (50 mph) in difficult conditions. The Highway Code (rule 227, page updated 22 October 2025) says that in wet weather stopping distances will be at least double those on dry roads, because tyres have less grip, and asks you to keep well back. Rule 126 says the two-second gap should be at least doubled on wet roads (Highway Code, rules 103 to 158; see our guide to stopping distances in the wet). NASA's own advice to drivers in 1963 was at least three times the normal spacing.
2. Switch off cruise control in heavy rain, as Michelin UK advises, so that you control the throttle.
3. Read the road. Look far ahead for puddles; avoid ruts, where water collects, and the edge of the road, where it drains to.
4. Check pressures monthly and before a long trip, at the car maker's figures (how to check).
5. Watch the tread, especially below 3 to 3.5 mm, where ADAC and Continental place the change in behaviour.
6. Avoid sudden inputs on wet roads: Continental names hard braking and accelerating as triggers.

A tyre's season matters too: the guide to winter tyres in the UK covers when each type works best.

What to do if your car aquaplanes

The signs, from Continental UK: steering that feels light or stops responding, the engine revving without the car speeding up, a whooshing sound, and traction or stability warnings. The Highway Code says that if the steering becomes unresponsive, water is probably preventing the tyres from gripping, and tells you to ease off the accelerator and slow down gradually. Beyond that, the sources differ:

The common ground is clear: no sudden steering, lift off the accelerator, keep the wheels pointing where you want to go. On braking, Continental and ADAC differ: Continental says to brake hard at once only if a collision is imminent; outside that case, every source asks you to wait for the grip to come back. ADAC and Michelin both insist on keeping the wheel straight until it does; our reading is that a wheel left turned at that moment can send the car off in the direction it points.

After driving through deep water, the Highway Code's rule 121 asks you to test the brakes gently at the first safe opportunity and to dry them with light pressure while driving slowly. If the car pulled, vibrated or hit something hard while you were in the water, have it checked before you get back on the road.

Frequently asked questions

What speed does hydroplaning happen at?

There is no single speed. NASA's formula gives about 10.35 × √(psi) mph: 56 mph at 2.0 bar, 61 mph at 2.4 bar. ADAC's tests on cars give 75 to 85 km/h (47 to 53 mph) for new tyres in 7 mm of water, and ADAC says the risk rises clearly from about 80 km/h (50 mph). Deeper water, worn tread and low pressure lower it.

Hydroplaning occurs when what happens?

When a layer of water builds up between the tyre and the road faster than the tread can clear it, and the water pressure under the front of the contact patch lifts the tyre. It needs enough water depth, enough speed, and a tyre that cannot evacuate the water.

Is hydroplaning the same as aquaplaning?

Yes. "Hydroplaning" is the usual word in the United States and Canada, and in NASA's papers; "aquaplaning" is used in Britain, Australia and in the tyre makers' European pages.

Do wider tyres hydroplane more?

ADAC and Continental say so: wide tyres, and wide low-profile tyres, aquaplane more readily, and in ADAC's tests only narrow 155 mm tyres could go above 90 km/h. ADAC's explanation: a wider tyre has more water to push aside, along longer paths. NASA's formula does not include width.

At what tread depth does aquaplaning get worse?

ADAC says it becomes especially critical below 3.5 mm and that from about 3 mm it can occur even on a damp road at 100 km/h when braking. The legal minimum is 1.6 mm in the UK, 1.5 mm in Queensland, and 2/32 inch in most US states according to Michelin.

Does tyre pressure affect hydroplaning?

Yes. In NASA's formula the speed rises with the square root of pressure, so a tyre 20% under pressure loses about a tenth of its hydroplaning speed. ADAC warns that over-inflation also favours aquaplaning. Use the car maker's pressures.

Should I brake when aquaplaning?

Not as a first reaction: the Highway Code, ADAC and Michelin say to ease off and let the car slow down with the wheel straight. Continental adds that if a collision is imminent you should brake hard at once.

Can heavy cars and trucks hydroplane?

Yes, though NASA found that the higher pressures of truck and bus tyres put their hydroplaning speeds higher than those of cars. Continental says heavier vehicles are not immune when tyres are worn or the water is deep.

Wheels from Onyx Forged

Onyx Forged is a French brand of made-to-order forged wheels, designed to JWL/VIA standards. The tyre on the rim decides how the car behaves in water; the wheel decides which tyre sizes can be fitted. If you are planning a set, see how a set is customised and check the sizes against your car's documents and your tyre fitter.

Sources

• NASA Technical Note D-2056, Phenomena of Pneumatic Tire Hydroplaning, Horne and Dreher, Langley Research Center, November 1963.
• ADAC, Aquaplaning, 16 October 2025 (in German).
• Tyre makers: Continental UK, aquaplaning; Continental UK, tread depth; Michelin UK, aquaplaning, 15 May 2025, updated 3 June 2025; Michelin North America, the truth about worn tires.
• The Highway Code, rules 226 to 237 and rules 103 to 158, updated 22 October 2025.
• GOV.UK, MOT inspection manual, section 5.2.3.
• Regulation (EU) 2020/740, Annex I, wet grip classes and European Commission, tyres.
• eCFR, 49 CFR 393.75, Tires.
• Queensland Government, Vehicle Standards Information 16, October 2021.

All pages were read on 16 October 2026. We could not read NHTSA's tyre pages or a Canadian provincial text for this guide.

The Onyx Forged design office.