GOOD MOTORING
Tyre care
H. Kishie Singh

A valve stem assembly (left) and a tyre pressure gauge.

THERE are so many different theories about tyres and inflation pressure — measured in per square inch (PSI) — that they sound like myths.

Today tubeless tyres are all the rage, and they behave in a different way than the regular tyres. They hold the car to the road, and provide cushioning on a bumpy road. They also provide efficient braking and roadholding.

They may, however, fail to do all this if the tyre pressure is incorrect. In summer, the pressure increases and it becomes important to maintain the correct tyre pressure. If you are not sure of the correct pressure for your tyre, call the tyre manufacturer or dealer for details.

Some tyres have the maximum tyre pressure printed on the sidewall. This is not always correct. For example, the same tyre can fit a Gypsy and a Tatamobile 207. Since the Gypsy is a passenger vehicle, and the 207 is a pick-up truck, the same tyre pressure won’t do for both the vehicles.

Lots of people fit 13-inch tyres on to Maruti 800s, which come with 12-inch tyres. This is not recommended, for you end up raising the centre of gravity and altering the handling dynamics of the car. The car could be quite unsafe. So the tyre pressure recommended on the sidewall could be misleading. In any case, never exceed the maximum pressure mentioned on the sidewall.

It is wrong to assume that an overinflated tyre is more likely to burst than an underinflated one. An underinflated tyre will face more rolling resistance and consequently, friction. This will build up heat. An underinflated tyre is more likely to burst. It is the leading cause of tyre failure.

Changes in the air temperature also affects the tyre pressure. This is more pronounced in hot weather. A change of 2-3`B0C could change tyre pressure by 2 psi.

Tyre pressure should be checked regularly for better fuel consumption. Don’t forget to check the pressure of the spare wheel.

Never "bleed" a hot tyre to reduce air pressure. All nozzles should have a cap to protect the valve from dust and water.

Earlier it was a common practice to change tyres but carry on with the old tube. Today, if you get a new set of tubeless tyres, make sure you replace the valve stem assembly. Over the years, the valve stem gets subjected to heat, dust and water. If the valve stem collapses, the air will escape in seconds. This means you could run on an absolutely flat tyre. For sure, your steel rim will cut the tyre to ribbons. It’s cheaper to replace the valve stem assembly than a tyre. The valve is the only inlet and, consequently, outlet for the air in your tyre. A new valve stem assembly costs about Rs 35 to Rs 50.

Here’s another recommendation for longer tyre life, better fuel average and safety. A tyre pressure gauge allows you to check the tyre pressure at home, easily and regularly. The pressure gauges at service station are misused and may give an inaccurate reading.

This gauge will also allow you to check air pressure when the tyre is cold. If the tyre pressure is higher, bleed it. If low, record the underinflation amount. For instance, if it should have been 24 psi but was 22 psi, the difference is of 2psi. Now at the service station inflate to the recommended 24 psi, by adding 2 psi. This helpful hint comes from the Tyre Industry’s Safety Council, USA.

Happy motoring.

This feature was published on October 2, 2004