Earlier in my career, I managed the North American operations for a German truck components manufacturer. One day, we received a warranty claim from a fleet customer. Our product was suffering premature failure. After a quick examination, I determined that it was being destroyed by road shock and vibration when operating off-road.
To determine the cause, the engineering director came over from Germany. The first place we took him was to a heavy truck dealership. We knew the dealer was preparing a chassis to mount a mixer. The chassis had a Hendrickson walking beam suspension with rubber block springs.
“Where are the springs?” the engineering director asked. We pointed and described the rubber block to him. “In America,” he asked, “is everything so heavy duty?”
It turned out our product had never been designed to resist the forces it was subjected to. In the concrete industry, many of the suspensions are designed to be “so heavy-duty.”
First, why do our trucks have suspensions? A suspension's primary purpose is to provide ride quality. They isolate the unevenness of the road (or off-road) surface from the truck's frame.
The suspensions absorb shock and isolate vibration so drivers and machinery aren't bounced around too badly and are protected from damage and injury.
Suspensions also keep tires on the road instead of letting them bounce off the surface. Without the suspension to keep wheels and tires in place, drivers could barely maintain and control trucks. Tires transfer the forces of acceleration, braking and turning from the truck to the road. But to do it all, they have to be kept on the ground in contact with the road under roughly the same load at all times.
Suspensions equalize the gross vehicle weight among all axles. If an axle and its wheels and tires and overloaded, the tires wear prematurely and are prone to blowouts. Axles could break. And without sufficient load on the tires, traction is reduced and the tires can't function properly.
They determine roll stability. If the roll stability factor is too low, a truck will tip over easily. Steering and handling may be adversely affected. But if roll stability is too high, the ride is rough and road shock transfers to the chassis.Three varieties
Manufacturers have addressed each of these roles a suspension plays by offering three types of spring media. Each type you will see has its own advantages and disadvantages.