Saturday, July 31, 2004



GOOD MOTORING

Tyre trouble
H. Kishie Singh

Tubeless radial tyres can cause blowouts because of their weak side walls
Tubeless radial tyres can cause blowouts because of their weak side walls

SO much has been said in favour of tubeless radial tyres and the fact that punctures donít really bother motorists any more. Since the tyre is tougher than a tube, it takes a long time for the air to escape from it when it is pierced by something sharp. The tread portion of the tyre is tough, but the side wall of a radial tyre is notoriously weak. The tyre wonít suffer a puncture, but what about a blowout?

To answer that I will share a personal experience with you. It happened on the Ring Road in Delhi which is strewn with debris because of the flyover being constructed.

I have four Bridgestone Potenza G.III tyres on my car. They are tubeless and unindirectional. I gather a piece of concrete or steel grazed the sidewall of the front right tyre. The cut went right through the sidewall and the air escaped. It was a blowout! The tyre was useless. The car was sitting on the rim. So much for tyres that donít suffer from punctures.

That was the first lesson to be learnt that day. The next 30 km and one hour were just as informative and educative. First I had to find a place to park and change wheels. And, that is not easy on the Ring Road. The tyre which had burst had been a unindirectional one. It was replaced with a multi-directional tyre. Now I had two different tyres on the front axle. In any other country this would have been illegal. The law requires that the two tyres on the same axle be identical. The same brand, same tread, and the same size. A very sound rule, as I was to find out. Immediately, the car started to pull to the left. The left tyre was providing more traction and rip on the tarmac, so the steering was favouring the left tyre. Constant correction was necessary to keep the car in a straight line. This was not a problem as it was stop-and-go driving along the Ring Road, using the first and second gear. Gentle breaking would swing the car to the left. After Azadpur, the road opens up. Since I was having a brand new experience, I decided to see how the car would behave at higher speeds. Badly. Very badly, I found out. The car had no stability in a straight line. Braking and cornering were non-existent even on a dry road.

Normally, this car, a Toyota Corolla, rides on the best tyres, Bridgestone Potenza G III. They provide one of the smoothest rides, combined with superb road holding, straight line tracking, braking and cornering. That day the drive was disastrous and all because of one tyre.

A simulated panic stop left me cold. I visualised a cow jumping onto the road from the centre median in front of the car. I stood on the brakes. The car came to a halt out only after describing an arc and pulling the car into the left-hand lane. Had I been in the left-hand lane, I would have ended up in the rough. Another problem. With the brakes locked, leaving tarmac and going into the gravel, would have further destabilised the car. There are thousands of eucalyptus trees along N. H. 1 which would happily stop you in case your brakes donít.

A few more tests of this very odd and bad combination of tyres and my first impression was confirmed. Avoid such a mix and match at all costs.

There was only one thing to do, change rear wheel to front since I had no spare wheel. For this, I needed two jacks, which I also did not have. So I was obliged to drive till the first tyre-walla. We jacked up the right hand side and moved tyres front to rear. Now there were identical tyres on the front axle. The odd tyre was on the right rear.

And what a change there was in the handling of the car immediately. The steering was responsive, the straight-line tracking was perfect, braking almost normal.

Happy motoring.

This feature was published on July 24, 2004

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