Shock Absorbers

Sun (Auckland), Volume II, Issue 486, 16 October 1928, Page 6

Shock Absorbers

What To Expect From Various Kinds SO long as the manufacturers continue the practice of building two-seater, four-seater, coach and van bodies on identical ehasses, the spring- suspension as us'ed to-day must remain largely as a compromise. More particularly does this apply to the light ear field, as will be apparent when the difference is noted when, say, three extra passengers are placed in a light car and the same number added to a bus.

ing the vibration, however, effectively prevents “galloping,” and makes the car a great deaL safer at speed, while not sacrificing comfort in any way at slower rates of travel. The majority of snubbers use the principle of a fabric strip operating over a spring-loaded disk; while others use the resistance of a plunger in a cylinder of oil. Another simple but serviceable spring damper takes the form of a specially-designed curved steel plate, bolted on each half of the spring, in a position midway between axle and shackle. The true shock absorber, however, operates in both directions—that is, it regulates the spring movement, both on compression and recoil. This friction shock type is simple in operation, one extremity being anchored to the chassis and the other to the axle, so that vertical motion is positively under control by the simple process of tightening a hexagonal nut on the central friction disk. EXTREMES So great is the range of adjustment that for road racing, when very stiff suspension is desired, the movement would be so small that to all intents and purposes the system would be rigid. At the other extreme of adjustment the car springs may be allowed full scope for movement, and any degree of damping between these wide limits is easily, secured. Of course, the ideal suspension system is that in which individual springing of each wheel is used, and those motorists who have driven the Lancia car will have pleasure in confirming my opinion. The loading factor of the springing is no longer important when this system is used. For the car rides quite as comfortably when driven fast over rough roads, whether lightly or heavily laden. Harking back to the shock absorber question, however, it must be pointed out to motorists that to drive a car—especially the American type with long, flexible springs—at high speed without some shock absqrber equipment, is courting disaster, and money spent on these fittings as extras is, in my opinion, a cheap insurance premium.

The springing of the light car chassis provides for a light load, and this extra weight is gross overloading —in the heavy bus the additional weight is of small moment. In order, to secure a smooth, swaying motion when travelling over rough surfaces, the majority of cars are equipped with long, flexible springs. While this serves a purpose, there is a very important aspect that must not be lost sight of—that is, the danger of high speed travel with light, flexible springs. Back-wheel “dither,” due entirely to this cause, has been the prime factor in many a serious crash. Now, as a set-off against this spring' compromise, and to ensure a reasonably safe and comfortable ride under wide variations of load and speed, a number of auxiliary suspension systems have been designed. AUXILIARIES FOR COMFORT They are divided, as follows, into three distinct classes, each with its particular field of application, and each having distinct limitation: Auxiliary springs or pads. Rebound dampers, or snubbers; special auxiliary leaves and spring dampers. True shock absorbers, functioning ! both against compression and rebound. Auxiliary springs or pads are usu- : ally affixed to the axle, directly under < the chassis, and are only designed to ■ prevent “crashing.” For the moment they may be overlooked. The next class, including rebound dampers and special spring dampers, : is more generally used. In order to < describe the purpose of these fittings, we must understand just how they do their work. A car spring may be likened to a tuning fork—it has a definite period of ■ oscillation. Shock absorbers are designed to damp out these vibrations and bring the spring to rest again in the most effective and rapid manner. WHAT SNUBBERS DO Snubbers place a check on the re- < bound movement of the spring, but do < not affect the compression at all. The fact of slowing down or damp- <