Rubber blocks, either in compression or shear, are rugged. They operate best when fully loaded, and offer a rough ride, bouncing tires off the pavement when running empty.
Multi-leaf steel springs are more easily tailored to varying loads. The first few leaves are bundled to take the weight of an empty truck.
Additional leaves bear on the first group, coming into play only as increased weight brings them into contact. At vehicle capacity, all leaves are in use and flexed.
When air suspensions were first introduced, fleet managers considered them too delicate for ready-mix trucks. In the last few years, they have become a viable alternative, but getting them accepted hasn't been easy.
In the ensuing decade, a great deal of progress resulted in new, rugged designs for air suspensions. “Our Primaax has high articulation and high roll stability,” says Jerry Remus, marketing manager for Hendrickson. “Customers get the benefits of a walking beam to equalize load between the axles while giving very good articulation. We also made the air springs very durable. There's even a weight savings of about 300 pounds between a Primaax and a 46,000-pound-rated steel leaf walking beam.”
Today, air suspensions are quite popular on front-discharge units. And air suspensions have been gaining attention on ready-mix trucks due to their characteristics when empty. Air is easier on equipment, more stable, and it provides a comfortable ride.Pump suspensions
Concrete pumps—which weigh virtually the same, loaded or empty, and could probably operate quite well with leaf springs specifically designed for the vehicle—are most often specified with air suspensions.
“Pumps get a better ride using air suspensions, and at Mack, we are successfully using air on mixers, too,” says Steve Ginter, Mack Trucks' marketing manager, vocational products, Air ride is available to 52,000-pound capacity, from Neway. “What is most important is the bags are self-equalizing,” Ginter explains.
Producers have been slow to accept air suspensions for rear-discharge mixers because of the perception of less roll-over resistance. Remus says today's air suspensions are far superior to those of a decade ago in stability and ground clearance. Both are serious concerns when running both on-and-off-highway.
And with the growth in horsepower and torque, suspensions have been designed to be non-torque reactive. They have more torque rods to transfer forces. Less suspension twist reduces pinion angle variation. That, in turn, reduces driveline vibration.