Replacing your Tyres

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Recently, one of our colleagues was involved in a high speed car accident, which could have turned out very seriously. Fortunately, they were OK, although the car certainly wasn’t.

Why are we blogging about this? Because the accident was down to fitting a pair of new tyres incorrectly, due to a simple, and avoidable error.

So what was this error?

Fitting brand new tyres to the front of a front wheel drive car, not the rear. Doesn’t sound so bad, but the results in the video below show that it so obviously is, as they were partly to blame for the spin in the bad weather. Let me explain…

On a car, when two or more tyres loses their grip on the road, the behaviour of the car, and the direction it moves in can change dramatically, and the inputs to the steering wheel may not produce what the driver desires, resulting in a loss of control.

Generally speaking, this takes two forms:

  1. Oversteer – when the rear loses grip first and the back end of the car moves round in relation to the front, often causing a spin.
  2. Understeer – when the front loses grip first and the car has a tendency to want to plough straight on, regardless of steering angle.

In the case of sudden, unexpected oversteer, applying the brakes only makes things worse. The back of the car is already moving faster than the front, and braking transfers more weight, and therefore grip to the front and away from the rear tyres, so it actually increases the chance of a spin and the speed of that spin when it occurs.

Applying more power has the opposite effect, transferring weight rearwards. This can help the rear tyres start to regain their grip, but time, space and a great deal of skill are needed to ride out the slide and recover control. This required time and space may not always be available though.

From this it can be seen that when understeer occurs, acceleration just produces more understeer, but easing off will bring the car back under control, due to the transfer of the car’s weight in relation to the front set of wheels.

And this is why, when you replace a pair of tyres on a front wheel drive car, you should always put the new ones on the back of the car, and the worn ones at the front, then should you lose grip for whatever reason, the car is more likely to understeer, which is much easier to control and recover from.

Happy Motoring!

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