Saturday, September 26, 2009

Front-wheel drive and hydroplaning safety

With so much water everywhere, it is a good time to warn people about the physics and dangers involved in front-wheel drive vehicles when they run into water puddles.

The drive shaft for the powered wheels (i.e., the ones providing the push) must have a differential that allows the wheels to spin at different rates. For example, when turning, the outside wheel must roll faster than the inside wheel.

The front wheels are the ones in front! Obvious, but that means they are the ones which hit the water puddles first. When wheels hit water, they have a tendency to hydroplane, i.e., float on the surface of the water, rather than clinging to the road's surface. Most roads are built up in the center, so water runs off to the edges. This means that water puddles are likely to be on the right hand side of the road as you drive forwards.

If the right wheel hits the water and begins to hydroplane while the left wheel is still on the pavement, the differential allows (actually causes) the right wheel to start spinning rapidly, because there is no friction on that wheel while it is floating. It only takes a second for the wheel to start spinning extremely fast, especially if the accelerator pedal is being pressed.

Now, consider what happens when you have landed on the other side of the puddle and your right front wheel is spinning at high speed. It will force the vehicle to veer to the left, directly into the on-coming traffic lane. If someone is there, a head-on collision would be unavoidable. Otherwise, it is likely you could spin out of control, especially if you overcompensated and turned the wheel to the right to avoid the collision. If you turn too far to the right too fast, you will skid, and the car will keep going in the direction you were trying to avoid.

Safe driving tips: When your car hydroplanes, remove your foot from the accelerator, and let the vehicle get on the other side of the water before you try to get back up to speed. If you find yourself hydroplaning, in addition to removing your foot from the accelerator, grasp your steering wheel tightly and keep it pointed in your original direction. If you are prepared for the lunge to the left, a steady grip can keep your car under control.

General rule: slow down when there is water standing on the roadway. It is when you are trying to accelerate that the danger is worst.