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Tyred and tested

We looked at tyres some time ago, and we learned that rubber is treated with sulphur (or “vulcanised”) so that it doesn’t melt when it’s hot and get brittle when cold

india Updated: Aug 27, 2009 16:05 IST
Grease Monkey

We looked at tyres some time ago, and we learned that rubber is treated with sulphur (or “vulcanised”) so that it doesn’t melt when it’s hot and get brittle when cold. If it did, it would be easier to use chocolate.

Radial tyres get protection in the form of steel, polyester, nylon or even kevlar belts to lend strength to the tread, the part that’s in contact with the road. Crossply tyres are made of textile weave under rubber, but they’re as useful to today’s cars as an abacus is to a computer programmer.

Go tall to weather shock...
The ‘aspect ratio’ of a tyre is the ratio of the height of its sidewall to its width in percentage. Crossply tyres have an aspect ratio of 100, which means that the height of the sidewall and the width of the tread are identical. They can be different in radial tyres — an SUV’s tyres are not too wide but certainly have really tall sidewalls. On the other hand, a low-slung sportscar will have tyres that look like nothing more than rubber bands stretched over the wheel rims.

A tall tyre will cushion shock easily. That’s why racing cars from Formula One have really tall tyres. These tyres do a lot of bump absorption so that the suspension doesn’t undergo too much stress. Off-roading vehicles also have similarly tall tyres, which help the car stay higher off the ground to avoid rocks and the such.

...and squat to stay grounded
Road-going supercars and tin-top racers, on the other hand, have really low tyres with really low aspect ratios, as this gives better road-holding ability and feedback through the steering wheel. The taller the tyre’s sidewall, the more it will bend if the driver goes fast through a corner, which is not desirable if he wants to place the car accurately, or make quick changes of direction.

The downside of low profile tyres is that they don’t absorb bumps that well, so they might not be such a good idea on our roads.

Don’t make a splash
The designs you see on your tyre’s tread aren’t there to make the tyre look good. What they do is prevent ‘aquaplaning’, also known as ‘hydroplaning’. We’ve all skipped stones on water at some point during our childhood. The stones skip over the water due to water’s ‘surface tension’ — the very same force that makes droplets of water drip from a tap when it isn’t shut properly, instead of letting it form a continuous stream.

If you drive too fast over standing water, the car will slide over the top of the water because the grooves in the tread will not be able to channel the water through them and let the rubber itself connect with the road beneath.

Think of the car as the skipping stone, only it isn’t as much fun for those in the car, since the driver will have no control until the car slows down enough for the tread to work effectively, or until dry road reappears.

This is a very good reason to slow down before you hit a puddle — leave the splashing through puddles to children.

Inspect your tyres regularly — if a single tyre looks less inflated than the others, it might have an air leak or a puncture. If the tread isn’t worn regularly, it might indicate suspension trouble. that is best nipped in the bud.

Your tyres keep your car glued to the ground, so take good care of them. They’re an oft-neglected but vital part of your car.

If you have questions or comments for Grease Monkey,
email him at carsnbikes@hindustantimes.com with Auto Tech 101 in the subject line