T R U CKS & T R A N S P O R TAT I O N
than air suspensions. They can also be designed to maximize stability. “A trade-off between articulation and stability is not necessary,” says Wrinkle. Mack offers its Camelback and mRide as examples that both offer high articulation and stability. It is important that any mechanical suspension used in a high articulation environment be able to evenly distribute the load. Freightliner recommends a trunnion suspension such as TufTrac, which is Daimler Truck North America’s proprietary suspension for Freightliner and Western Star trucks. “Trunnion suspensions are best suited to handle bumps and ridges without bottoming out,” says Howerton. “TufTrac specifically keeps a uniform load over each wheel during articulation.” Walking beam suspensions have traditionally been favored for high articulation applica-
systems are also extremely durable. “Depending upon the spring medium design, walking beam suspensions can have a little bit harsher ride and may require more maintenance, because they have a more complex design [than spring steel suspension systems],” notes Howerton. The primary benefit of the walking beam design is its ability to equalize the load. “Modern walking beam designs are integrated into advanced rubber spring systems, which bring additional benefits to the suspension system,” says Remus. “Walking beam suspensions have advanced to provide the highest amount of articulation while achieving the stability required for off-road work.” In high center of gravity applications, you will want to consider the benefits of a mechanical suspension. “Mechanical suspensions with
“The floating beam suspension with soft ride restrictor can provide a superior ride quality that compares favorably with air ride when on the road.” — Billy Alford, Southeast regional sales manager, Chalmers Suspension International
It is important that any mechanical suspension used in a high articulation environment is able to evenly distribute the load. Freightliner recommends a trunnion suspension, such as TufTrac, which is Daimler Truck North America’s proprietary suspension for Freightliner and Western Star trucks.
tions. “Floating walking beam suspensions allow maximum articulation and can offer maximum roll stability,” says Alford. “The floating beam suspension with soft ride restrictor can provide a superior ride quality that compares favorably with air ride when on the road. This feature is available for specific truck applications and tractors, as well.” Walking beam suspension
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high roll stiffness and high roll centers are best suited for high center of gravity applications like concrete mixers,” Wrinkle asserts. High center of gravity loads pose a unique concern. “Peterbilt generally recommends non-air ride suspensions with high center of gravity loads,” says Cook. The stability of a walking beam suspension can be a definite advantage in these applications. “It is important
to choose one that can distribute the load equally to all four wheels even during severe articulation,” advises Alford. “That can be done by choosing a floating beam suspension, which is suited specifically for high center of gravity applications.” Restricted movement in the spring translates to increased stability. “Walking beam suspensions are best suited for high center of gravity applications because they are the most roll stable due to limited movement and compression within the suspension spring,” says Remus. The design of the spring in a walking beam suspension determines several performance characteristics. “Walking beams offer articulation to some degree, but in most designs they are somewhat heavy. And when used in conjunction with [steel] springs, they become even heavier,” says Alford. “The walking beam when paired with rubber spring technology results in an ideal suspension configuration,” Remus states. “Rubber spring components are less weight, easier to maintain and provide greater ride quality and stability over steel spring suspension systems.”
Rubber load springs may also increase durability. “Component fatigue always finds the weakest point,” says Alford. “But with the innovative design of the floating beam and rubber load spring, instead of the heavy leaf spring, a great balance has been achieved concerning weight and durability.” Finding the correct balance is key. “We can spec a suspension that provides the best balance
between stability and articulation,” says Peterbilt’s Cook. “For instance, we offer suspensions with very high articulation, and when more stability is required, there are optional High Stability Restrictor Cans.”
AIR SUSPENSIONS PROVIDE BEST RIDE QUALITY It’s hard to beat air ride for driver comfort. “Driver comfort and a shortage of drivers are the main reasons for the increase in the move to air ride suspensions,” says Alford. “Creature comfort and the reduction of shock to other components of the chassis are real reasons to look at air ride.” That said, it does have limitations. “No manufacturer has been able to offer both stability and articulation with air ride.” Air ride suspensions continue to expand in certain vocational applications, such as dump trucks and heavy-haul tractors. “Air ride suspensions provide consistent ride quality in any load condition, which will help lessen driver fatigue while protecting equipment and chassis components from damaging vibration and road inputs,” says Remus. A primary benefit is enhanced unladen ride quality. “Air suspensions have gained in popularity in certain vocational applications thanks to their better ride when empty, and constant ride height,” explains Wrinkle. “Computer modeling has helped make many advances in suspension design at a faster rate than before. These advances have helped address some of the weight and strength concerns through the use of innovative materials and designs. “Despite these advances, air suspension systems still demonstrate less articulation and stability than mechanical suspensions,” he continues. “Specific driver training may also be required, with the need to evacuate air bags before dumping the load.” Weight savings is also an advantage with air ride systems. “Some mandated federal requirements, such as SCR and DPF, have added weight to trucks, which is one reason customers are moving to the lighter air ride suspensions,” says Howerton. “While they are not the best for every job, they provide ample capability and capacity for dump applications.”
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7/14/16 8:51 AM