Wednesday, May 11, 2011

Tires behavior : Hydroplaning

Hydroplaning is sliding of a tire on a film of water . Hydroplaning can occur when a car drives through standing water and the water cannot totally escape out from under the tire. This causes the tire to lift off the ground and slide on the water. The hydroplaning tire will have little traction and there for, the vehicle will not obey the driver’s command.

Deep grooves running from the center front edge of the footprint to the corners of the back edges, along with a wide central channel help water to escape from under the tire.

There are three type of hydroplaning; dynamic, viscous, and rubber hydroplaning. Dynamic hydroplaning occurs when standing water on a wet road is not displace from under the tire fast enough to allow the tire to make pavement contact over the total footprint. The tire ride on a wedge of water and loses its contact with the road. The speed at which hydroplaning happens is called “Hydroplaning speed (VH) ” that is estimated in knots by equation 1

VH = 9*P^0.5 -------(1)

Where P is tire inflation pressure in psi

For a matric system would be

VH = 5.5753 x 10^-2*P^0.5

Where P is tire inflation pressure in Pa

VH is in m/s

Rubber hydroplaning is generated by superheated steam at high pressure in the tire footprint, which is causes by the friction generated heat in a hard braking.

Viscous hydroplaning occurs when the wet road is covered with a layer of oil, grease, or dust. Viscous hydroplaning happens with less water depth and at a lower speed than dynamic hydroplaning.

Ref. Vehicle Dynamics: Theory and Applications , Reza N. Jazar

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