Formula One: Trend of design

Anti-roll bar controls

There is a surprising divergence of opinion on the use and function of the suspension anti-roll bar. Everyone is agreed that suspensions front and rear need the operation of a subsidiary torsion bar to control the degree of roll when cornering, but the difference of opinion comes in whether the driver should have any control over the operation of the torsion bar and, if so, how it should be done. The anti-roll bar, which is a steel bar being used in torsion, or twist, has the effect of controlling the amount of roll that the car undergoes due to weight transfer, side-to-side, when cornering. The resultant effect is the roll-stiffness and this affects the characteristics of a tyre following the undulations in the road and the loads on the tyre when cornering. A total lack of roll-stiffness would mean that the car would flop over towards the outside of a corner due to centrifugal force acting on the centre-of-gravity of the car. Because racing cars have different suspension systems and geometry front and rear, each end of the car needs its own anti-roll bar, and because there is more weight at the rear of a Formula One car than at the front the rear anti-roll bar has to be stronger than the front one. The amount that the steel bar resists twisting is dependent on its length, diameter and the leverage applied to either end to twist it. Consequently anti-roll bars can be effectively altered by using a variety of differing diameters, or by altering the lengths of the operating arms.

Exactly how much roll-stiffness is considered desirable depends on a number of variables and the choice is almost infinitely variable, so that an optimum setting is chosen, dependent largely on the whim of the driver or the choice of the designer. As the roll-stiffness can affect the cornering characteristics of the car you can play about with the anti-roll bars until the cows come home, Mario Andretti and Colin Chapman developed the fully adjustable anti-roll bar with the Lotus 78, in which a system of cables and levers enabled the driver to adjust the roll-stiffness from the cockpit, ranging from virtually no roll-stiffness at all to being virtually solid. This was done by the ingenious expedient of coupling the ends of torsion bar to the suspensions by two arms approximately eight inches long, one of these arms being in the form of a blade of steel which could be rotated about its longitudinal axis. In one plane this blade presented a rigid beam which did not bend, but when rotated at right angles it presented a thin blade that was virtually a spring leaf with no rigidity at all. These two extremes were imparted to the torsion bar so that in one position the suspension movement twisted the bar to the maximum and in the other position it twisted the bar hardly at all, and the amount of twist reacted against suspension movement when one side was trying to go up and the other side down, as when cornering. Over a straight line bump both operating arms rise or fall together and there is no twist on the torsion bar.

It was a simple matter to couple the movable arm or blade to a cockpit control by means of links and a long cable and Lotus still use the same principle of a push-pull control on the left of the instrument panel for the front anti-roll bar and a fore-and-aft sliding lever, with seven notched positions, on the left of the cockpit for the rear anti-roll bar. This set off a popular trend and most designers used similar controls at some time or another, but as the effectiveness depended to a large extent on the sensibility ot the driver, many of them soon disappeared and any changes in roll-stiffness were effected by the designer in known steps, either by changing the actual torsion bar or altering the lengths of the operating arms along known graduations.

A rundown on the various teams at the German Grand Prix produced a surprising variety of opinions. McLaren, ATS, Ensign, Alfa Romeo, Arrows and Osella provide no controls at all for the driver, any changes that are deemed necessary are effected by the mechanics in the pits under the direction of the engineer in charge. These changes are made either by substituting a different diameter bar into the mechanism, as with McLaren, or altering the lengths of the operating arms by movement of a clamp, as with Osella. Tyrrell, Brabham, Fittipaldi  and Lotus all provide the driver with cockpit controls for both front and rear. As already mentioned Lotus use a push/pull control for the front, push the knob in for maximum roll-stiffness, pull it out for minimum and Tyrrell use a similar system. The Lotus rear control is a slider knob on the side of the monocoque, and this has seven positions, Tyrrell use a similar system but with only five positions. Brabham control their front one by a knob on the right of the instrument panel which you turn either clockwise or anti-clockwise. This turns a quick-start threaded rod on which a collar moves, the collar being coupled to a push/pull cable that runs to the anti-roll bar movable link. The rear control on the Brabham is similar to the Lotus, with a slider knob on the left side of the monocoque and a cable running to the rear. Like the Tyrrell there are five positions for this knob along the slider, and forward gives maximum roll-stiffness, or hard, and rearwards gives minimum, or soft. Fittipaldi have a unique system of a slider-control on each side of the monocoque, the right-hand one, coloured blue, for the front and left-hand one, coloured red, for the rear.

Renault, Ligier and Williams only give the driver control over one anti-roll bar. In the case of Renault and Ligier it is the front one and with Williams it is the rear one; Williams used to use a front control, but have now abandoned it, and are in the process of abandoning the rear one as well. Renault provide control of their front anti-roll bar with a slider-knob on the left which has five positions, while Ligier control their front one by a knob on the left of the instrument panel, which you turn either way, utilising a quick-start thread like Brabham. Instead of rotating a blade-shaped operating arm on one and of the torsion bar, as most people do, theirs moves the bottom of a vertical operating link to and fro thus altering the effective length of the operating arm. Williams use a simple cable system like Lotus, with a slider-knob on the left of the cockpit, with seven positions.

Never a slave to fashion, no matter how good it may seem, Ferrari are unique in using a system that couples the front anti-roll system to the rear system by means of rods and cables. Where this control rod passes the cockpit on the left a short lever is introduced that operates on a rack and pinion principle and movement of the lever forwards or backwards has the effect of softening the front and stiffening the back and vice-versa. This system comes directly from that used a few years ago in which the front and the rear anti-roll systems were coupled together hydraulically with an over-riding mechanical control to the rear one.

Although most designers have experimented with driver-controlled anti-roll bars, the fashion is dying out as they discover that their drivers are insensitive to changes or are unable to make suitable changes relative to the requirements. A driver like Andretti, when he was on top of his form in the Lotus 78 could alter the roll-stiffness front and rear a number of times in a lap, which made delicate control of the car that much easier. His team-mate at the time was Ronnie Peterson, who never understood the finer points of chassis and suspension tuning or balance, and merely drove fast by animal instinct. After both drivers had recorded identical practice laps you could look at the controls and find Andretti had his at one end of their movement and Peterson would have his at the opposite ends, Andretti refused to describe exactly how he “trimmed” the car with these controls. Peterson was very straightforward; he left them the way he found them when he got into the car. While Peterson’s super-fast lap would be an inspired “one-off’, Andretti could guarantee to repeat his to order and for any number of laps.

Cockpit control of the anti-roll bars would seem to be an idea that is fast going out of fashion. — DSJ.