Front Suspensions
Early car designers had the experience of carriages to work with as they were designing their vehicles. The rigid front axle of the horse-drawn carriage, steered by being pivoted about its centre, more or less enforced the design of a suspension system that sprung both wheels and the axle together. Axle steering had great disadvantages for the higher speeds of powered vehicles. Soon the wheels were steered by pivoting on the axle ends, and designers concluded that it might be better to spring the front wheels independently, so that when one wheel met an obstruction it did not affect the other wheel.
The idea was a good one in many ways, but unfortunately nobody at that time realized the side effects of wheel movements. Little by little knowledge was gained of the movements and forces involved, often more by trial and intuition than by mathematical deduction. It was probably not until the publication of the work of Maurice Olley, after he had left the Rolls Royce dealers for General Motors, and Donald Bastow of Rolls-Royce and Lagonda in the mid-1940s, that the mechanism of independent front suspension and steering began to be understood fully. A car cornering with an old-type beam front axle and leaf springs would have an equivalent transverse spring length of about two feet (60 centimetres) that is, the distance between the springs and would roll about an axis midway between, and at the height of, the springs.
With a change to a transverse leaf spring system which allows the front wheels to rise or fall independently, the transverse spring length was doubled. Consequently the resistance to rolling was greatly increased. But, because the spring allowed the body to tilt while the spring ends remained at an equal height, the centre about which the body rolled moved down to ground level. This increased the distance between the centre of roll and the centre of gravity, through which the rolling force acted. Thus the tendency to roll also increased. With the transverse leaf spring, or the equivalent of equallength, parallel links and coil or torsion bar springs, any vertical movement of a wheel relative to the chassis results in a reduction of wheel track, as the spring deflects to move the wheel closer to the chassis. The result is a sideways tyre scrub that can damage the tyre tread. To obviate this track change, which also has a steering effect on the car, the links were made of unequal length, longer on the bottom, so that the wheel tilted inwards at the top as it rose. This kept the track more or less constant and had produced a bonus by raising the roll centre.
All of this experience has led to the fantastic handling capabilities that we find nowadays in cars such as the new Rolls Royce ghost and the spectacularly smooth riding Bentley Continental. We have much to thank these early designers for.
