Animated suspension for your comfort

By Barry Lake

RIDE comfort and excellent handling are at opposite ends of the spectrum in motor vehicles.

Car company engineers spend more time researching and developing ride, handling, road-holding and noise, vibration and harshness (NVH) qualities than any other aspect of their work.

It's not that providing a car with the right power and torque characteristics, exhaust emission levels, gear ratios, braking and so on is easy.

It is more to do with the fact that ride, handling, road- holding and NVH can be such obscure goals.

They are neither easy to define nor to describe, let alone to achieve.

But they are vital in terms of selling cars and for the subsequent comfort and safety of the people who use them.

You might assume -- as U.S. carmakers once did -- that soft springs would give a car good ride. But they don't.

A car with soft springs will float along the road like a row boat in a swelling sea, making its occupants sick.

A car with soft springs will also roll too much in corners and leap about on humps and bumps, spoiling its handling and road- holding capabilities.

It is possible to dampen the action of the springs by the use of shock absorbers (more correctly known as dampers) and it is also possible to limit body roll in corners by fitting antiroll bars which resist roll.

But much of the comfort initially aimed for would then be lost.

And therein lies the inherent problem -- all of these goals are interrelated.

You change one, you almost certainly create an effect upon the others, usually adverse.

It becomes a seemingly never-ending ritual of trial and error and the end result is always a compromise to some degree.

This is why there are usually various versions of popular car models, including a "sports" version.

People who enjoy driving will choose a car with sharp handling and good road-holding qualities.

It will be a stiffer ride with increased transmission of "bump and thump" to the interior of the car and a harshness of ride which comes from a combination of stiff-walled lower-profile tires, stiffer springs, harder shock absorbers and harder suspension bushes.

But the levels of noise, vibration and harshness are unacceptable to people who prefer to amble along at more sedate speeds.

These people rate comfort, quietness and a luxurious feel above the ultimate in handling and road-holding.

But car companies can't sacrifice too much in the way of handling and road-holding in the quest for comfort.

A car still has to be safe to drive, predictable in its handling and capable of staying on the road when driven at faster speeds, no matter how much comfort is the goal.

In the same vein, a car with sports-type handling and road- holding still has to have a certain degree of comfort.

At the sports car end of the spectrum, there would usually be low-profile tires on wide wheels, quite stiff springing, more heavily damped shock absorbers (in both bump and rebound) and suspension bushes made from quite stiff materials.

Such a car would be sharp in its response to driver input (handling) and retain good grip on the road through corners (road-holding).

But it would transmit the shock from road bumps, the noise and vibration from the tires and the action of the suspension components more readily to the interior.

Thus, limousines have higher-profile tires with softer walls; softer springs; more progressive damping -- especially in bump -- from the shock absorbers; and more flexible, sound-deadening and shock-absorbing suspension bushes.

The difficult task for engineers is to constantly bring these two extremes closer together.

Electronic control of hydraulic dampers is a step in the right direction.

Either the driver or a preprogrammed computer varies the damping effects of the shock absorbers to suit road conditions and driving styles.

If pneumatic springs become more common, they could be computer controlled and infinitely variable. Roll stiffness could also be controlled in this way.

Suspension bushes have become increasingly sophisticated in recent times with the use of varying materials and clever design, which allows bushes to be stiff in one plane (say, fore and aft) while being relatively soft in another plane (up and down).

Suspension design has become so refined that ultralow profile tires, which once would have been unbearably stiff to drive on, are fitted to an increasing number of cars, with surprisingly good results in terms of ride.