good motoring
Tyre size does matter
H. Kishie Singh

ONE sees a lot of cars on the road where the owner has fitted oversized tyres on the car. One can use a tyre that is only marginally larger than the one manufacturer has given.

However, big tyres jutting out from the wheel arches, mounted on expensive mag wheel ruins are often seen. The only good these wheels do is for your ego. It does nothing for the performance of the vehicle. On the contrary, it may adversely effect the braking and cornering of the vehicle, thereby making it unsafe. In the pre-ABS era it was an accepted fact, wide or extra-wide tyres are not recommended because the car would not then behave in the manner it was designed for. This can be downright dangerous especially if the braking and cornering abilities are compromised.

In the post-ABS area that we are in now, the manufacturer specifically states that fitting oversized tyres will effect the functioning of the computer-controlled ABS equipment on board.

The computer is programmed, say, to receive original from 165-R-60-13. It may put up with say 175-R-60-13 tyre size but if you go for 205 cm tyres, the ABS will malfunction.

Stick to what the manufacturer says because the latter knows much more than you do about the cars design, function and performance.

With each drop in temperature by 6`BAC, the pressure of the tyre, measured in pounds per square inch (PSI) falls by one PSI. This means driving a car from Delhi to Shimla and parking over night could see a change in temperature from about 20`BAC to 25`BAC in Delhi to Shimla’s near-zero or even sub-zero temperatures at night.

This would drop your PSI by two or three. If it is your front tyres that have unequal tyre pressure, it would give you a very poor ride on a hill road. Since most cars front-engine and front-wheel drive, this effects your steering. The car would turn easier in one direction. In an emergency, this could lead to a dangerous situation.

On hill roads in winter, there might be snow on the roads or pot holes, for this one needs accurate steering. Uneven tyre pressure may deny you this.

A recent survey in the United Kingdom showed that 50 per cent of cars on the road had under-inflated tyres. If this happens in an informed society, one fears statistics for India would be dismal.

Another point to keep in mind some air-gauges at petrol pumps are famous for mal-functioning. It would be a good idea to check tyre pressure at more than one petrol station.

One can buy a small tyre pressure gauge for personal use. They are not expensive and they can be accurate. The results are a better ride, a better average and a longer life for tyres.

There is another rule in force abroad regarding tyres on the same axle i.e. a pair is a must. In Sikkim the same tread, same manufacturer for the front tyres are mandatory. And they must be original i.e. no retreads. These rules have been arrived at after years of research and have been made for the purpose of safety.

If your tyres are other than what is specified in the technical specifications for your cars, you could invite a challan.

Happy Motoring.