Water Skidding 101: What is Hydroplaning?

If you haven't noticed, we humans evolved into almost the perfect organism. Not only can we make some amazing things with our genius brains, like, for example, cars, but we can also drive them pretty successfully on any path and during every weather.

Put accent on "pretty," because although we are good at driving in various conditions, we are not perfect at it. But that is not an inherent problem to "Homo Sapiens." Thinking about it, modern self-driving systems with gazillions of bits of computer data are still much worse drivers than us simply because road conditions are so varied.

Drivers shouldn't only care about accelerating, turning, and braking. You should also take care of other (jerk) drivers and various road conditions. One occurrence that still scares most drivers today is hydroplaning, which happens mostly during heavy rain, mixed rain, snow precipitation, and melted snow on the road.

But what is hydroplaning, and why do publications like us often mention it in tire reviews? Well, the simple answer is that it is standing water that prevents the tire from remaining in contact with the road. However, like with all things automotive, the full answer is much deeper.

So, buckle up and join me on a journey where we will find answers on how to minimize skidding on water and explain the science of hydroplaning. Let's dive in!

Understanding Hydroplaning

Hydroplaning also referred to as aquaplaning in some English-speaking countries, is a phenomenon that occurs when a layer of water builds between the tires of a vehicle and the road surface, leading to the loss of traction that prevents the vehicle from responding to control inputs like steering, braking, or accelerating.

Most drivers are sadly not versed in the phenomenon. You can see them driving at high speeds when it pours outside, only then to lose control of their car and cause a big accident. It is an issue that still plagues road safety today – 10% of all car accidents are caused by rain alone. Also, 6,000 people were killed and over 445,000 injured (according to the NHTSA) due to weather-related accidents.

So, understanding the hydroplaning phenomenon is crucial for every driver, as it can lead to potentially dangerous situations if not properly managed. If you aren't sure what hydroplaning is, I suggest paying close attention, as there are many factors involved.

1. The Science Behind Hydroplaning

Hydroplaning essentially happens due to a struggle between the tire tread and water depth. As your vehicle moves, its tires must displace the water beneath them in order to maintain contact with the road surface.

To be able to channel that water out of the contact point with the surface, modern tires have carefully designed tread patterns. These include large circumferential grooves connected to lateral grooves, which channel the water out of the tread and keep the tire in contact with the road.

Still, the tread pattern has a finite displacement property, i.e., it can't displace infinite amounts of water. Even the best rain tire will hydroplane eventually – it is just a matter of the amount of water, the speed you are traveling, the weight of your car, and the state of the tire (pressure, tread depth, and width).

What I learned in the past two decades trying all sorts of cars on very wet surfaces is that when a car hydroplanes, it essentially becomes akin to an uncontrolled sled. The tires lose almost all contact with the road, making it extremely difficult to maintain or regain control of the vehicle.

Hydroplaning is a nightmare for even the best racing drivers. If you watched Formula One, you would know that when it rains, drivers start to skid and uncontrollably, often hitting the barriers. And all of that happens while they are driving much more slowly than on a dry track.

Furthermore, this phenomenon doesn't just occur with standing water – slushy conditions from partially melted snow can also lead to hydroplaning. In fact, in these conditions, the partially melted snow might make things even worse and keep the tires from touching the road at much lower speeds.

Hydroplaning is largely a matter of physics. The speed at which a vehicle will hydroplane can be roughly calculated by the formula: 9 times the square root of the tire pressure in psi (pounds per square inch).

For example, for a standard passenger vehicle tire with a pressure of 32 psi (2.2 bar), hydroplaning may begin at approximately 51 mph (82 km/h). This is not a hard and fast rule, as other factors such as tire wear, water depth, and vehicle weight will affect this, but it gives an approximate guideline.

2. What Triggers Hydroplaning?

Several factors contribute to the onset of hydroplaning. I will list them in no particular order, as depending on the vehicle and tire combo, each one will have a different effect on the phenomenon.

• Tire tread depth: new tires with full-depth grooves will have a lower risk of hydroplaning. Thus, as the tread wears down, your tires will be more susceptible to the issue, with hydroplaning appearing at lower speeds and less standing water. Of course, regular tire inspections and replacements can help mitigate this risk.
• Vehicle speed: the speed you are traveling at is directly proportionate to the risk of hydroplaning. In other words, the faster a vehicle travels, the harder it is for the tires to disperse the water beneath them, increasing the chance of water building up under the tires. Thus, I highly recommend slowing down when it rains, as it will dramatically lower the chance of hydroplaning happening.
• Water depth: hydroplaning is most likely to occur when driving through deep puddles of water, i.e., when there is more water than the tire can displace at that certain speed. Heavy rainfall, melting snow, poor road drainage, or uneven tarmac can create conditions ripe for hydroplaning.
• Tire pressure: underinflated tires have a higher risk of hydroplaning. There are a few factors that come into play here. For starters, the tire loses its regular shape, reducing the effectiveness of some of the grooves. However, underinflation also makes the contact patch larger, which disperses the weight of the vehicle on a larger area. This also leads to hydroplaning because the tire won't "cut" through the water as easily.
• Tire (tread) width: the tread width of the tire (the first number in tire dimensions) can also affect hydroplaning, with wider tires being more susceptible to the issue. This happens because the weight of the vehicle is dispersed on a larger area, which leads to flotation. Moreover, the increased surface area has to displace more water, and if the water can't be channeled away quickly enough by the tire treads, it can lead to an increased risk of hydroplaning.
• Vehicle weight: as the previous two factors probably taught you, weight plays a big role in hydroplaning, with lighter cars being much more susceptible to the issue. This happens because they don't press down on the road surface as much, making it harder for the tires to displace water effectively.

Hydroplaning and Tire Performance

The occurrence of hydroplaning has a significant impact on the overall performance of a vehicle. When hydroplaning takes place, the tire loses contact with the road surface, which reduces traction drastically. As a result, you may completely lose control of your vehicle, i.e., you won't be able to turn, brake, or accelerate.

1. How Tire Tread Affects Hydroplaning

The most important role of the tread on modern tires is to reduce hydroplaning. Hence, every tire comes with numerous grooves designed to channel water out of the tire's contact patch with the road. Some tires are obviously better than others, but every modern tire can channel a significant amount of water from the contact patch.

With that said, new tires with deep grooves will reduce the likelihood of hydroplaning. Therefore, if you live in an area where it rains frequently, it's crucial to replace your tires once the tread reaches a certain depth.

Authorities require replacing the tires at 2/32 inches (1.6 mm) of tread depth (the depth indicators are flush with the tread) because that is deemed enough for successful hydroplaning. However, if you care about your safety, I suggest replacing the tires much sooner, like, for example, when the tread depth reaches 4/32 inches (3.2 mm).

2. The Role of Tire Pressure in Hydroplaning

Tire pressure is another crucial factor in hydroplaning. A properly inflated tire can help prevent hydroplaning as it ensures that the tire maintains an optimal shape and surface contact, allowing the tread to work effectively.

Meanwhile, underinflated tires are much more likely to hydroplane. Namely, an underinflated tire will distort its shape, which might cause some of the grooves to close down, i.e., become smaller. This would make them less effective at channeling water, thus increasing the chances of hydroplaning. Also, underinflated tires won't cut through the water as easily because they disperse the weight of the vehicle on a larger area (just like wider tires).

But overinflated tires are also not as good in rainy conditions, although they might reduce the chances of hydroplaning. Namely, an overinflated tire will concentrate the weight of the vehicle on a smaller area but will have lower overall traction due to the smaller contact patch.

The manufacturer-recommended tire pressure on your car will provide the optimal balance between hydroplaning resistance and wet grip. Therefore, it is crucial to keep your tires properly inflated at all times or near the recommended pressure. I suggest checking the pressure at least once every month or before a longer journey.

3. Tire Width and Hydroplaning

Wider tires provide a larger contact patch with the road, which improves grip. However, this is also detrimental when it rains, especially during heavy rain.

Namely, wider tires will disperse the weight of the vehicle on a larger area, essentially introducing floating. In other words, they won't cut through the water as easily. However, to keep a wider tire in contact with the road, the tread needs to displace much more water, which further increases the chances of hydroplaning occurring on wider tires.

Meanwhile, narrower tires, with their smaller contact patch, have less water to displace, which allows them to maintain better contact with the road surface. Also, because they concentrate the weight of the vehicle on a smaller area, they will cut through the water more easily, thus resisting hydroplaning.

With that said, while wider tires are generally more prone to hydroplaning, they will still perform better on damp roads and on roads where there is no standing water. In those circumstances, the wider contact patch reigns supreme and provides a higher grip than a narrower tire.

4. Hydroplaning: Radial vs. Bias Ply Tires

The type of tire construction can also influence the propensity to hydroplane. Radial tires, with their flexible sidewalls, tend to maintain better road contact under different conditions, including wet surfaces. This can help reduce the risk of hydroplaning compared to bias ply tires, which are much stiffer overall.

Fortunately, most tires designed for highway use, i.e., driving at higher speeds, have a radial construction. Today, bias-ply tires are only used on special agriculture and construction vehicles and on some ATVs and UTVs.

Vehicle Factors in Hydroplaning

Although they play the biggest role, your tires aren't the sole contributor to hydroplaning – the vehicle also plays a big role. Namely, certain characteristics of your vehicle, like its weight, suspension system, and speed, also affect hydroplaning.

1. How Vehicle Weight Impacts Hydroplaning

Vehicle weight definitely affects hydroplaning, but not as much as you'd think. Indeed, a heavier vehicle can press the tires more firmly against the road, theoretically increasing traction. Thanks to the added weight, the tires will also cut through the water more easily, which assists with water dispersion.

However, it can also induce more water pressure at the tire-road interface, increasing hydroplaning risk. This is common on heavy cars with very wide tires, especially when the tires aren't inflated properly.

2. The Influence of Speed on Hydroplaning

Speed is a crucial factor in hydroplaning. At low speeds, tires have more time to displace the water they encounter, thus maintaining contact with the road surface.

However, as the speed increases, the tires won't have enough time to move the water out of the contact patch, which raises the chances of a water layer standing between the tire and the road.

For those reasons, it is crucial that you always slow down when it rains. That is because hydroplaning can destabilize your car in an instant – everything will be fine up to the moment your car skids out of control.

3. Vehicle Suspension and Hydroplaning

The health of your car's suspension also plays a crucial role in hydroplaning. For instance, worn-down dampers can cause the wheel to jump uncontrollably over the road, thus preventing it from keeping firm contact with the road. If the tarmac is wet, this could introduce hydroplaning and lead to a loss of control. Therefore, it is crucial to maintain the suspension and check for issues regularly.

Summer vs. All-Season vs. Winter Tires When It Comes to Hydroplaning

Not all tire types provide the same hydroplaning resistance. Due to their different designs and constructions, summer, all-season, and winter tires bring different attributes to the table, influencing the likelihood of hydroplaning. So, which tires are the best choice to alleviate the issue?

1. Summer Tires

Although this surprises many drivers, summer tires actually provide the best hydroplaning resistance. This is especially true for grand-touring and max-performance summer tires, which are not designed with track use in mind, i.e., they have wider and deeper grooves. Track-focused summer tires, though, sacrifice hydroplaning resistance to maximize dry grip and have fewer grooves on the tread.

With that said, the tread pattern on grand-touring and max-performance summer tires is specifically engineered to prevent hydroplaning by efficiently channeling water away from the tire's contact patch. These tires have very wide circumferential grooves connected to lateral grooves for a successful water evacuation.

Moreover, the softer rubber compound on summer tires helps them maintain a grip on the road, further enhancing wet traction.

As a result, summer tires deliver superior hydroplaning resistance in rainy conditions compared to other types of tires.

2. All-Season Tires

All-season tires look like they can handle quite a lot of water, and indeed they can. However, they can't compare to summer tires when it comes to hydroplaning resistance because their treads are also designed to tackle snow with smaller sipes across the tread blocks. In addition, all-season tires usually have smaller longitudinal grooves, which makes them slightly more prone to hydroplaning.

Other than that, the rubber compounds of all-season tires are harder, which may slightly decrease grip in extremely wet conditions compared to summer tires.

3. Winter Tires

Winter tires are crafted with a special rubber compound that remains flexible in extremely cold temperatures, ensuring optimal grip on snowy and icy surfaces.

However, winter tires don't provide the best hydroplaning resistance because their tread design is more focused on biting into snow and ice rather than displacing water.

Furthermore, the softer and more flexible compound of winter tires can become too soft above the freezing point. This distorts the tire's shape and closes the grooves, which increases the chances of hydroplaning (similar to an underinflated tire).

Environmental Conditions Leading to Hydroplaning

The environment is the biggest factor that contributes to hydroplaning simply because the issue is inherently a weather-related phenomenon. With that said, various factors can influence the chances of hydroplaning occurring, so let's have a closer look at that.

1. The Effect of Rainfall on Hydroplaning

The amount of rain is directly correlated to the likelihood of hydroplaning because the more it rains, the more water accumulates on the road. Of course, this all depends on road drainage – in some places, even light rain can lead to hydroplaning.

With that said, while hydroplaning might not be an issue after the first few minutes of rainfall, traction will be the lowest during that time. That is because the first rain mixes with oil residue and other debris on the road, which creates an especially slippery surface.

After the initial phase, the rain essentially cleans the roads from oil and other residue (provided there is good drainage), which increases traction but also increases the chances of hydroplaning occurring.

2. How Road Conditions Contribute to Hydroplaning

As everybody knows, not all roads are the same. Some roads with poor drainage, for instance, can increase the risk of hydroplaning. Moreover, roads with large irregularities, like deep depressions and potholes, allow for the water to pool, creating ripe conditions for hydroplaning.

Overall, roads with a convex design are best at reducing hydroplaning because they drain the water successfully by design. Moreover, rough tarmac provides much better traction in wet conditions than smooth tarmac, especially during the first few minutes after it starts raining. So, keep that in mind the next time you are driving down a rough road, and you protest how loud it is.

Regular road maintenance and effective drainage systems can, therefore, play a significant role in mitigating the risk of hydroplaning.

Preventing Hydroplaning: Safety Measures and Best Practices

Of course, you cannot control weather or road conditions, though, for the latter, it is crucial to always vote for politicians that promise regular road maintenance. Still, you can maintain your vehicle and adjust your driving style, both of which can significantly reduce the likelihood of hydroplaning occurring.

1. Regular Tire Maintenance to Prevent Hydroplaning

Tires that aren't maintained or replaced regularly are much more likely to hydroplane. And all of this starts by choosing the right type of tires for the weather conditions in your area. So, if you live in an area without any snow during the winter, it is probably wise to invest in summer tires and not in all-season tires.

Furthermore, ensuring that your tires are correctly inflated can significantly reduce hydroplaning. Underinflated tires have a larger contact area with the road and closed-down tread grooves, both of which increase the likelihood of hydroplaning. Meanwhile, overinflated tires reduce the contact area and can cause tires to ride on the center tread, which can also increase the hydroplaning risk.

But the age of the tire also plays a huge role. For instance, tires without sufficient tread depth will hydroplane much more easily, which is why you should replace your tires once they reach the lowest legal tread depth (2/32 inches or 1.6 mm).

Moreover, the rubber compound on all tires changes its chemical structure as it ages in a process called dry rotting. This makes the compound harder and less sticky, thus directly affecting its traction properties, particularly over wet and snowy surfaces. Therefore, even if your tires have enough tread depth left, you should replace them after 6-8 years (depending on the model).

2. Safe Driving Techniques to Minimize Hydroplaning Risk

Apart from making sure your tires are up to the task, you should also self-evaluate as a driver and make sure you are ready to tackle heavy rain. Fortunately, this doesn't require some superior driving knowledge or experience – all you need is to follow these simple steps, and the likelihood of hydroplaning occurring will be much lower.

For starters, you should always adjust your speed when it rains, i.e., slow down. This is something that many drivers forget, only to find themselves in very dangerous situations. Furthermore, you should try to avoid puddles of standing water on the road, which present a higher risk of hydroplaning.

But, contrary to popular opinion, you shouldn't avoid the puddle at all costs, i.e., you shouldn't suddenly turn the steering wheel. Smooth application of the brakes, accelerator pedal, and steering wheel ensures that your vehicle doesn't lose traction or hydroplane.

In addition, you should always keep a safe distance from the car in front of you, which is particularly true when it rains or snows. This gives you more time to react to changes in the road condition or other drivers' actions.

Finally, here is some expert tip: if you're following another vehicle, driving in their tire tracks can help you avoid hydroplaning, as it will displace some of the water.

Hydroplaning and the Modern Vehicle

Modern vehicles are much safer than ever before, thanks to advancements in suspension design and especially driver's aids. These active safety systems work proactively to minimize the odds of the car losing control and help the driver regain control if hydroplaning occurs.

1. How Vehicle Technology Helps Prevent Hydroplaning

Almost every modern car that is on sale today is equipped with a plethora of sensors and computers that monitor how the vehicle behaves to enhance road safety. Technologies like traction control (TCS), vehicle stability control (VSC), and anti-lock braking (ABS) can detect stability issues much sooner and take immediate action to prevent the vehicle from losing control.

2. ABS, Traction Control and Vehicle Stability Control: Hydroplaning Deterrents

Anti-Lock Braking Systems (ABS), for instance, prevent the wheels from locking up during heavy braking, maintaining the driver's ability to steer while braking. It is a mandatory technology on all new cars in most markets nowadays and can be crucial during hydroplaning scenarios where the vehicle might start to skid on a waterlogged surface. This allows the driver to maintain steering control while braking, which is crucial for maneuvering away from danger.

Meanwhile, the Traction Control System mitigates wheel spin during acceleration. The system monitors a discrepancy in wheel speeds and cuts down power when necessary. During hydroplaning, various wheels can move at different speeds; hence, traction control might prove crucial in reducing hydroplaning. In those cases, the TCS will use the brakes to reduce the power to the affected wheels, thus keeping the vehicle in the desired driving line.

Finally, the VSC, or Vehicle Stability Control (referred to as Electronic Stability Control (ESC) by some car brands), ensures that the car stays stable when turning into a corner, even when hydroplaning occurs. It does that by monitoring the steering wheel's position and the direction the vehicle is moving. If it detects a disparity — say, the driver is steering to the right, but the vehicle continues to move straight ahead due to hydroplaning — the system intervenes by applying the brakes on some wheels. As a result, it can keep the vehicle in a desired line during cornering.

All of these systems add a considerable layer of defense against hydroplaning. Thus, it is safe to say that cars equipped with ABS, TCS, and VSC are much less likely to skid out of control. However, it is important to note that these systems only reduce the odds of hydroplaning – they don't eliminate it entirely. Therefore, everything we said about tire maintenance and driving more slowly still applies.

What to Do If Your Vehicle Hydroplanes

Everything we talked about up until this moment is how to prevent hydroplaning from ever happening to you. But the truth is that hydroplaning has happened to almost every driver. So, in the event it happens, how should you react? Here are some expert tips.

1. Immediate Response to Hydroplaning

Common errors that drivers make when they realize the car is hydroplaning are braking or steering slightly. This would only make things worse, as it could destabilize a car that has little to no contact with the road and hence, no traction.

Instead, you should just ease off the accelerator slightly and gradually reduce the speed. Since the standing water will provide quite a lot of resistance, the speed of your car will reduce significantly in a second or two, and you will regain control, i.e., the tires will touch the tarmac.

2. Regaining Control After a Hydroplane Incident

Once you feel you are in control, you can start steering smoothly if you need to turn or start braking if you need to stop. I would always suggest pumping the brakes lightly, though, on cars with ABS, the system will take care of the things for you. Once your tires regain traction, you can regain control and continue driving, albeit more cautiously. Remember that experiencing hydroplaning once means the conditions are right for it to happen again.

Conclusion

Was this article in-depth enough for you? If it wasn't, there is a plethora of science journals that explain the issue in more technical terms online – just Google it!

But really, the bottom line is that hydroplaning requires mindfulness from the driver. Just the thought of it, when you are driving during heavy rain, will make you feel more comfortable because you will likely slow down. Always think about the driving conditions and use your acquired knowledge to increase your own safety, but also the safety of your family and others.

Furthermore, being mindful of the state of your car and its tires can bring you safely to lots of places. You might fool others but don't fool yourself with those severely worn-down tires, as they might come back to bite you. Also, make sure your vehicle is always in tip-top shape before hitting the road, as it is your own safety we are talking about here!