Effects of underinflation
Remember, underinflation is one of the greatest killers of tyres. Tyres running at less than optimum pressures can suffer a 25% loss in tread life due to increased shoulder wear. They are also dangerous.

The worst thing is, you won’t even know your tyres are nearly flat (i.e. running at pressures as low as 10 psi or 70 kPa) until it’s too late. Most motorists believe that a discerning driver would know when his tyres are underinflated because he would feel the drag produced by the deflating or flat tyre.

But that’s not the case.

In reality, the drag effect can’t felt, thanks to the greatly advanced designs in modern vehicle suspension. In particular, it’s almost impossible to tell a rear tyre is underinflated.

By the time you find out about the flat tyre, its sidewalls would have fallen apart.

Effects of overinflation
Don’t pump too much air into your tyres either.

Gross overinflation causes your tyre to bulge out at the centre. Which means that the centre of the tread will come into greater contact with road surfaces than any other part of the tread. So, the tread centre wears out earlier.

Because an overinflated tyre has a smaller surface area in contact with the road than properly inflated tyres, it suffers from reduced traction.

Overinflation of tyres also increases the risk of bruise damage. That happens when your tyre hits an object but you can’t really tell.

Tyres which are grossly overinflated also create undue strain on your car’s suspension.

So what’s the correct pressure?
You’ll have to check your car owner’s manual for the appropriate air pressure.