Good question for the rainy season! When most people buy new tyres, they tend to install them in the front axle. They give a number of reasons for doing so, among which are:
1. With the engine in the front, new tyres should be in the front since they are stronger and should be able to effectively support the weight of the engine.
2. New tyres will be less prone to suffer a blowout and since blowout of a front tyre is more dangerous than that of a rear tyre, it is safer to install new tyres in the front.
3. Front tyres suffer the rigours of acceleration, braking, steering and bad road conditions more, and so, wear out faster than the rear tyres. Therefore, new tyres are better installed in the front.
The foregoing reasons sound logical, but unfortunately, following that logic would land you in serious trouble. It is downright dangerous to install new tyres in the front axle, especially during the rainy season. Why? Because of a phenomenon called hydroplaning.
What is hydroplaning?
You will observe that your tyres, if not worn out, have some grooves and channels on the treaded portion that is in contact with the ground. Those grooves and channels are designed to, among other functions, help to remove water under the tyres on a wet surface so that the tyres will maintain adequate contact with the road surface for proper traction.
A situation may arise where the channels are not able to remove water fast enough or where the channels are not deep enough because the tyres have worn out. In either situation, the tyres will not maintain contact with the road surface and will simply float on the pool of water. This phenomenon of floating on water because of lack of contact with the ground is called hydroplaning. It is dangerous and may lead to loss of control and a crash. When a vehicle is hydroplaning, application of the brakes will make matters worse!
Now, let us consider the effects of hydroplaning with new tyres in (a) the front axle and (b) the back axle.
New tyres in the front axle and old tyres at back axle
New tyres, by nature, should have more tread depths than tyres in use. So, the tyres at the back – because they have less tread depths – will hydroplane before the new tyres in front. With the rear tyres hydroplaning first, a situation called OVER STEERING may occur. This is a situation where the rear tyres will lose traction before the front tyres and the rear of the vehicle begins to slide.
Oversteering is far more difficult to control, and, in addition to the initial distress felt when the rear of the car starts sliding, quickly releasing the gas pedal in an attempt to slow down, may actually make it more difficult for the driver to regain control, possibly causing a complete spinout, loss of control and a crash.
New tyres at the back axle and old tyres in front axle
When you have new tyres at the back axle, the old tyres in the front will hydroplane before the back tyres. This may lead to UNDERSTEERING. This means the vehicle will continue to move in the straight forward direction, even when you want to steer it either to the left or to the right. This is easier to control. By easing up on the gas pedal, the vehicle will slow down and make it very easy for the driver to control.
Members of The Tire Rack team had the chance to experience hydroplaning at Michelin’s Laurens Proving Grounds. Participants were allowed to drive around a large radius, wet curve in vehicles fitted with tyres of different tread depths – one vehicle with new tyres on the rear and half-worn tyres on the front, and the other with the new tyres in the front and half-worn tyres on the rear.
The ability to sense and control ‘predictable under-steer’ with the new tyres on the rear, and the helplessness in trying to control the ‘surprising over-steer’ with the new tyres on the front was emphatically proven. It is better to experience this phenomenon in the safe, controlled conditions of Michelin’s Laurens Proving Grounds rather than in traffic in a rainstorm. (Cont’d next week).