Aquaplaning (also water smoothness ) refers to the floating of the tire on the film of water a wet road. In this case, a wedge of water pushes under the tire contact area and thus leads to loss of adhesion. At the moment of aquaplaning no guiding and braking forces can be transmitted to the road. The vehicle can then go into a skid.
- 4.1 Preventive Measures
- 4.2 Countermeasures to aquaplaning
- 4.3 Common Misconceptions
- 4.4 Effects on other types of vehicles
Hydroplaning is a - in comparison to the history of the automobile - relatively young concept. Hydroplaning was not discovered until the early 1960s when the development work in the tire industry. As a result, the physical principles have been researched and developed countermeasures. Through magazines, TV commercials ( The seventh sense) and other media of the first exotic technical term has been increasingly known to the general public. Today, the knowledge and the prevention of aquaplaning important components of driving education are. As a frequent cause of accidents hydroplaning has an important role in the accident research.
The following sections relate to - if not expressly described otherwise - on passenger cars on the road.
The most common hydroplaning occurs in passenger cars on the road.
Physical and conceptual delimitation
Hydroplaning is not to be confused with the lower friction on wet surfaces, in which the road " slippery " or " smooth " may seem like a dry road surface. Have tires on a wet road in principle a lower friction coefficient than on a dry road, which makes, for example, in the extension of the braking distance noticeable and affects all types of road vehicles.
Due to the lower friction in wet conditions, the maximum possible lateral acceleration decreases (curve speed limit ).
The synonym water smoothness is misleading insofar as the other types of slippery roads, such as packed snow or frost smoothness are characteristics of the road, while hydroplaning is more of a driving condition, which only occurs in the combination of several factors.
Hydroplaning occurs when the displaced from the oncoming tire water on the road can not drain fast enough. The standing water like a wedge slides under the tire and separates it completely from the road. Upon occurrence of hydroplaning, the friction between tire and road is very low, thus steering or braking forces can hardly be transferred to the road.
Physically act here the inertia of the effluent water and lack of drainage in the tire ( negative profile outrageous or too low for the speed ) together.
In a vehicle with two axles, the following cases can be distinguished mainly:
- A single wheel floats on: In general, a yaw moment about the vertical axis, which the driver can control by braking occurs. The control of the vehicle is maintained. However, the vehicle is in the physical limits, so that further disturbances (eg, strong crosswinds, evasive maneuvers ) can lead to a complete loss of control over the vehicle.
- Both front wheels first float on: This case is most easily controlled, because the vehicle is traveling straight on the one hand and the longitudinal axis of the vehicle is supported by the rear axle in the direction of travel. Once the phase of aquaplaning ends, the driver regains control of the vehicle.
- All wheels swim simultaneously: Here it is from the center of gravity and the uniform distribution of wheel forces depends on how the vehicle behaves. Equal forces and an emphasis on the longitudinal axis of the vehicle lead to the same behavior as with floating front wheels.
- Both rear wheels first swim on: Here the vehicle begins to spin immediately. Even if hydroplaning is over, the vehicle is suspected in a situation in which the driver can hardly regain control.
In addition to the recommendation, in principle, reduce the speed in the wet, the result of the dynamic driving point of the recommendation to drive on the rear axle the tires with the best profile. If surprising hydroplaning occurs, it begins at the front axle and the driver can be adjusted to best meet the dangers.
Various factors are involved in the development of hydroplaning:
- Speed : The higher the vehicle speed, the greater the risk of aquaplaning; the vehicle velocity is the only factor which can be influenced by the driver of the danger of aquaplaning immediately.
- Thickness of the water film: With increasing height of the water film increases the risk of aquaplaning. The height of the water film on the road is the result of the dynamic equilibrium between of falling water amount (precipitation ) with the amount of water that can flow from the roadway.
- Type of roadway: The nature and construction of the road influence, for example by the slope and curvature of the roadway drainage of water. In lowering or turning points of S- curves water can collect, track damage as ruts or depressions lead to a locally strongly varying thickness of the water film. Lane roads lead to increased construction of the water film.
- Roadbed: By the choice of the building material of the outer layer and the drainage cavities can be affected. In impervious surfaces increase the risk of aquaplaning Little drainage. This aspect is taken into account in the planning and construction of roads.
- Tire tread depth: With the negative profile and greater tread depth of the tire decreases the risk of aquaplaning. The negative profile is influenced mainly by the tire manufacturer and tread depth the state of wear of the tire.
- Tyre Width: Wide tires tend somewhat more likely to hydroplaning than normal or narrow tires. Sophisticated tread geometries have managed the tire manufacturers to keep even with the wider tires aquaplaning within reasonable limits. But this is true only for " ordinary " tread depth. Very critical if wide tires be driven with low tread depth.
- Tire pressure: Inadequate tire pressure increases the risk of aquaplaning. At low tire pressure increases the contact area of the tire with the road, thereby reduces the " pressure " ( force per unit area ) of the tire to the road - a wedge of water can slide easily under the tire contact patch. Low tire pressure has another adverse effect: The tire contact area is slightly curved inwards from. The lateral displacement of the water is difficult and the risk of aquaplaning increases.
- Tire make and type (summer / winter) tire tests show that the various tire manufacturers and -finished products cut quite different during aquaplaning. Here, the described - or - wet performance as above, the rubber composition has little effect, but rather the profile shape and the portion of the negative profile.
- Shocks: Worn shock absorbers can increase the risk of aquaplaning. Functioning shock absorbers ensure that the force with which a tire is pressed onto the road in all driving situations remains as evenly as possible. If this is not fulfilled, ie, if this force is also only briefly reduces, hydroplaning can occur.
- Vehicle weight: The effect of the vehicle weight on the risk of aquaplaning is relatively low. The unnecessary increase in vehicle weight is not a meaningful measure to reduce the risk of aquaplaning represents a fully occupied and loaded car has only a slightly lower risk of aquaplaning when the tire pressure was increased accordingly.
Hydroplaning can be avoided by the driver in an actual driving situation by driving style and speed. Regardless of a specific driving situation can be prevented mainly by the tire tread.
As stated in the dynamics section, the tires with the best drainage should (ie with the lowest profile in the same tires) are mounted on the rear axle:
- Especially for front-wheel drive car with the same tire sizes on front and rear axle can be combine efficiency and safety when changing tires, two new tires mounted on the rear axle, and the existing tires of the rear axle to be changed to the front axle.
- For vehicles with uneven tire wear between front and rear axle should try the first set of tires by axle- frequent tire replacement, tire to drive with less remaining tread on the front and then to pursue the said tire change strategy drives the front.
Experience has shown that narrower tires are more resistant to aquaplaning and cost-effective, especially in winter operation may occur due to narrower tires further advantages.
Countermeasures against aquaplaning
If hydroplaning occurs, hazards can be mitigated through various measures:
- Avoid Brakes: A braked wheel can block while of floating. The wheel can no longer roll over the wedge of water, whereby the aquaplaning phase and thus the loss of control may extend beyond the vehicle itself. Gets the locked wheel after hydroplaning back ground contact, can lead to a unilateral aquaplaning yaw moment and cause lateral skidding.
- Avoid strong counter-steering during aquaplaning phase. Once the wheels get back ground contact, the vehicle could take in another direction journey, which will be answered intuitively by the driver fixes and so leads to skidding of the vehicle.
- Foot off the gas and disconnect the power flow as possible ( clutch pedal, automatic in N ), wait until the end of aquaplaning.
- Steering wheel straight and hold for lateral drift only slightly counter-steering.
- " ABS, ESP and four-wheel drive help against hydroplaning. " It is true that ABS and four-wheel drive can not prevent aquaplaning. If the vehicle is floating, the ESP can help only insofar as it lowers the engine's power, even against the will of the driver. After the end of the hydroplaning ESP can help to retain the driving stability, and to recover.
- " For a motorcycle is no risk of aquaplaning. " It is true that one can have with the bike hydroplaning and that this inevitably leads to a fall.
- "One should always be oriented in heavy rain at the speed of other road users. " It is true that the speed at which hydroplaning occurs, it can be very different from vehicle to vehicle.
- " Hydroplaning only occurs at speeds above 80 km / hr. " It is true that the combination of several unfavorable factors also significantly below 80 km / h already hydroplaning can occur.
- " The best tires on the front axle must. " Occasionally, more widespread in the tire trade advice and especially the owners of front drives recommended. The right thing to always be fitted to the rear axle in terms of traction and drainage best tire.
Effects on other types of vehicles
- Trucks and buses: In several sources it is stated that there could be no aquaplaning due to the high weight for heavy truck. The main reason is the low speed compared to cars For coaches, the speed limits are higher, so that the risk of aquaplaning increases.
- Motorcycles: On a motorcycle, there are two features that reduce the risk of aquaplaning: The opposite lower car tire width and tire cross section of the round - thus the water can be easily dissipated to the side. But motorcycles also have properties that increase the risk of aquaplaning: The vehicle weight is much lower than for passenger cars. In addition, the front wheel is more vulnerable to hydroplaning than the rear wheel.
- Aircraft: Because of the high speed when landing on wet runways hydroplaning can occur.