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Suspension systems

Have you ever taken a ride in a bullock-cart? It’s slow and it’s bumpy.

india Updated: Aug 27, 2009 10:01 IST
Grease Monkey

Have you ever taken a ride in a bullock-cart? It’s slow and it’s bumpy. The bumpy bit could be due to unpaved roads, but the real reason you will wish you had brought a cushion along is the lack of a suspension system on the cart.

If you look carefully at a vehicle in motion, you’ll notice the wheels keep moving up and down, following the road, while the body stays steady. This is possible because, unlike the bullock-cart, the wheels aren’t attached directly to the body.

Motorcycle suspension systems are relatively simple, since the major part of various forces act on the suspension in the vertical direction. Of course, in the case of riders who love corners, that doesn’t apply all the time. Vehicles with more than two wheels have more forces to contend with, and this makes them more complex.

All suspension systems have one thing in common — their aim is to keep the tyre in contact with the road surface as much as possible. This is necessary because the less the tyre is in contact with the road, the less it can be controlled. Racing cars do this really well, but one of the downsides is, you can feel the shape of every stone that went into the making of the road. And considering the usual state of our roads, you’d be better off in the bullock-cart.

On the other hand, if you have a comfortable, soft suspension tuned to absorb bumps, it tends to make the car’s steering feel very vague — the next time you’re on the highway and a pesky taxi you’ve been honking at takes forever to make way for you, remember because of his soft suspension, he has as little an idea of where he’s headed as you do.

An empty dump truck going at speed over bumps is a perfect example of a too-hard suspension, and a BEST bus going round a corner is the, well, ‘best’ example of a soft suspension. The truck’s bouncing and the body lean the bus achieves is due to the suspension’s hard or soft characteristics. Car manufacturers therefore spend lots of money on research and development of suspension systems that will not be uncomfortable for the occupants over bumps, and will still steer accurately.

Each wheel of a vehicle is attached to a spring and damper, which is in turn bolted to the car’s chassis. The spring helps cushion the shock, and the damper stops the rebounding motion from going on and on, otherwise the car’s body will keep bobbing up and down like a small raft on choppy seas.

A simple way of checking a damper’s health is to press down on a corner of a car and release it suddenly. If the car goes up and down more than twice, the damper needs attention. Some suspension systems perform the same functions but without a spring and damper. A dump truck has ‘leaf springs’, which are simply strips of metal of different lengths tied together that the truck’s body rests on.

They are not as sophisticated or compliant as modern arrangements, but they deal with massive loads the best.

This is why American muscle cars still use them, as does the Ford Endeavour. Cheap cars use a simple arrangement known as a torsion bar suspension for the rear — the more sophisticated ones use ‘multi-link’ units.

These help the wheel stay upright in any condition.

If you’ve ever accelerated sharply with your front wheels turned all the way, the outside wheel will squeal. This is due to the wheel not remaining vertical and thus losing grip.
The magic that goes into your suspension deserves a more intricate explanation. We’ll certainly revisit it.

Meanwhile, cut that taxi driver some slack. He’ll move over. Eventually.

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