SUSPENSION PROBLEM

Evening Post, Volume CXXVI, Issue 134, 3 December 1938, Page 28

SUSPENSION PROBLEM

CONFLICTING ENDS

THE MAIN CONSIDERATIONS

An engineering topic of recent months in the motor journals has been the subject of springing. The user of a motor vehicle is apt to think of springing only from the point of view of easy riding and comfort, and some drivers are like that too. Easy riding, however, is incidental to good springing, arising not from being pursued as an end in itself but out of ends of much greater importance that must be achieved in the interests of safety, economy, and the well-being of the vehicle itself.

The enormous improvement that has been apparent in motoring from all the aspects of easy riding have arisen not from advances in springing design but from modern road construction and surfacing and the strides

; achieved in the manufacture of tyres. Springing, itself, has remained a problem on which no finality has been reached, and there has been a great ' deal of see-sawing with one style and another, with shock-absorber devices actually providing most part of the advances achieved. The springs have imposed on them . . . the task of keeping the car speady at all speeds and on corners, and in securing good wheel adhesion on rough roads. These desired abilities are rather conflicting, and the designing of a suspension system which would have all of them is really difficult. It is easy enough to design springs which will be beautifully comfortable and soft in their action at moderate speeds, but at higher rates these will be likely to induce dangerous bouncing of the car, or at best an up and down motion that can be decidedly uncomfortable and has been known to make rear-seat passengers exceedingly sick. It is also quite simple to design the springs so that the car will remain rock-steady at speed and on corners, but at more normal rates of travel such springing will likely be unduly harsh. Rear wheel adhesion on rough surfaces is one of the greatest problems. The object is to build a car the wheels of which will follow the contours of a road surface without causing more than a very minor amount of vertical movement no matter what the speed is, that will corner without heeling over, and that can be accelerated on rough surfaces within reason without causing wheel-spin. Many cars come close to this ideal, but none quite get there. Independent front springing makes a car steady on reasonably soft straight roads and gives admirably soft springing at all speeds and on all surfaces, j One or two types of independent front suspension cause a certain amount of unpleasant rise and fall without, strangely enough, disturbing the car's straight path, while in some instances fast cornering is rather unpleasant. Many makers still pin their faith to the solid front axle, but while they) attain excellent cornering qualities and road steadiness, few provide springs as soft in their action as those! with independent suspension, neither are they, as a rule, quite as steady at speed. One of the reasons for this is that the front springs have to be stiff enough to withstand the twisting action of the brakes when these are applied. Several makers have improved spring action by attaching torque rods to the front axle, running back to the frame, so that the springs have only to suspend the car and therefore, can be more flexible. Independent springing for all four wheels is a theory accepted by practically all designers, but its practical application bristles with difficulties. It has been found essential, however; for the very light and fast European racing cars, which would not otherwise hold the road. That seems to indicate, also, its great desirability for touring vehicles. A great deal more may be heard of torsion bar • suspension, in which spring action is provided by the carefully* calculated resistance of a steel bar to the twisting strain imposed by the up and down movement of the wheel.