PROBLEMS OF SPRINGING

Press, Volume LXIX, Issue 21050, 29 December 1933, Page 4

PROBLEMS OF SPRINGING

INDEPENDENT SYSTEM A NEW TYPE PROPHESIED At present there appears to be considerable difference of opinion among experts on the likelihood of independent springing being adopted by a majority of ear manufacturers. At the recent Olvmpia motor show only one or two makes were equipped with independently-sprung front wheels, but at the Paris Motor Salon many wellknown producers exhibited new models in which either the front or all four wheels bad individual springing. Because of that trend in European design, it might be thought that, in due course, British car factories would be forced to adopt the practice, but although some of the leading European car builders have favoured this arrangement, many others equally eminent retain the conventional suspension with semi-elliptic springs and hydraulic shock absorbers. An excellent summary of tiie problem has been published in the British motoring press by Captain SmithClarke, a director and chief engineer of the British Alvis Company. This year two interesting Alvis models with independent front springs have been placed on the market, and Captain Smith-Clarke's exeperience of the subject began in 1900, when he improvised a simple system of independent front springing, building the mechanism from parts salvaged from a wheelwrights' scrap-heap, and fitting it to a smali three-wheeler.

Principle Wrong

lie asserts unequivocally that the ordinary form oC springing is wrong in principle, is the source of many troubles, and will prove to be more inefficient as the demand for uniformly good action at both low and high speeds increases. On the other hand, he is equally emphatic that unless independent suspensions are carefully designed they will fail in their purpose, and prove unsatisfactory. In indicating the orthodox design, .it is pointed out that such faults as wheel-wobble and bad road holding are often caused by synchronous vibrations and other reactions which are unavoidable with the normal system. Shock absorbers, steering dampers, and improved spring shackles, he states, are merely palliatives, and the necessity for using them is a clear admission of the inefficiency of the ordinary leaf spring. Even the best of modern cars often develops wheelwobble and other symptoms at certain critical speeds, and Captain SmithClarke's chief contention is that the usual type of springing is critical in action, and responds disturbingly to any minor loss of adjustment, such as play in the steering connexions, wrong tyre pressures, or a slight error in wheel balance. He states thai a welldesigned method of controlling each front wheel independently enables almost all the customary front-end troubles of motoring to be avoided, but he is not so enthusiastic with regard to thQ value of independent rear suspension.

Spring Deflection,

Tho principal advantage which it offers is a lowering of the unsprung weight of the car. Against that benefit must be weighed the reduction of ground clearance which, it is said, cannot be adequately maintained un<less the rear springs are so unresilient that their deflection is considerably curtailed, with a consequent loss of riding comfort. It has been estimated that for best and most comfortable riding at slow speeds the rear springs should be capable of a deflection of from seven to 10 inches, whereas at fast rates above 60 or 70 miles an hour a different condition is desirable, and deflection should be limited to four or five inches. Up to a point that variability has been achieved by the use of adjustable shock absorbers, controlled from the instrument board of the car, a refinement of design which is to be found on several makes of car. Captain Smith-Clarke concludes his statement with a prediction of an entirely new type of suspension which might be evolved. "To venture a prophecy,'' he says, "I believe that in years to come compressed air will be found to offer the correct solution. One can imagine a system which would be replenished automatically from an engine-driven pump, combined with a facia control whereby the driver could set the pressure in the suspension cylinders for soft or hard riding, according to the rate of travel. Used in conjunction with hydraulic damping, I believe that a pneumatic suspension would have f/reat possibilities, but it will probably be some years before a satisfactory arrangement of this kind is developed, owing to its unorthodox character and the prolonged experimental work required."