Saturday, July 3, 1999
THERE are newer tyres in the market for your car and some ofthe newer cars come with power steering. Both determine the handling characteristics of the car. These are referred to as over steer or under steer.
The tyres these days are mostly radial in construction. This means the side walls are soft. So, they are more prone to distortion while cornering when lateral forces are applied. Keep in mind that the car is glued to the road by four small patches of rubber! You could be cornering at speed and centrifugal force will try and make sure you dont come out of the corner. Centrifugal force will make the car "slip" all four tyres will have a slip angle and it will be unequal. This is due to the weight of the car, centre of gravity, condition of the tyres, tyre air pressure, and the road itself (wet or dry, smooth or (pot-holed). There are many variables here and they all play an important part in the ability of the car to go around a corner.
Ideally, a car should have a neutral steering to corner perfectly i.e. the trajectory of the car into and out of the corner should be a smooth curve keeping to the middle of the lane. This seldom happens, as there are far too many factors that could be working against you.
If a car goes wide at a corner it is said to under steer. It is entirely possible it may continue its trajectory and go in line straighter than the curve of the road. You could end in a ditch! Cars with front engine and rear-wheel drive tend to under steer.
Most cars today are front-engine, front-wheel drive. This changes the C.O G. dramatically and drastically and in turn the changes are felt in the steering. The car has a tendency to over steer. If the steer trajectory is not corrected, the car will make a loop and leave the road on the drivers side.
A car with front-engine and front-wheel drive, power steering and radial tyres will have a tendency to over steer.
Keeping this in mind, manufacturers have put in safety features into steering and suspension. The arrangement is as follows: In case of an "out-of control" situation, the driver will automatically, defensively take his foot off the accelerator. This reduces the power to the wheels and gives the tyres and chance to re-purchase a grip on the road. This is why good tyres are important.
Most drivers in the city may not notice these affectations of the steering. But drive an old Amby or Fiat and then get into a new breed with power under the bonnet, power steering and radial tyres. Instantly the difference will be felt. If the driver is careful, he will feel the car has a mind of its own during hill cornering. This can be dangerous. The driver must be in control of the car at all times, especially while cornering hard. It is at high speeds that the over steer or under steer tendencies of the car manifest themselves. A lonely road at night, no traffic would be a good time to familiarise yourself with these handling characteristics. If you are caught unawares on a crowded road the results could be nasty.
Understand your car. Get used to its handling characteristics. And most important, keep the car road -worthy. The tie rod ends, the brakes, the tyres should be in good condition. Its no use having good tyres if the tyre pressure is wrong. A small oversight can destabilise the car. Be aware of your car, road condition and traffic at all times.
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