When it comes to applications such as dump trucks, flatbeds and cement mixers, on front and rear discharge mixers, as well as trucks in refuse applications, tank trucks in oil and gas, and trucks in municipal applications, lift axles are a popular option.
“Lift axles are very different from steer and drive suspensions. Unlike drive suspensions, they consist of a non-drive axle. These axles can be round like trailer axles, they can be of the forged I-beam or fabricated style like the front steer,” explained Jason Heath, product manager, NEWAY Truck, Bus and RV Suspensions, SAF-Holland Inc. “Typically, non-steerable lift axles utilize a round trailer style and the steerable lift axles use the fabricated style or the round trailer style. Lift axles also have a unique lifting device that is not present on drive and front steer suspensions.”
SAF-Holland’s NEWAY LSZ Auxiliary Steerable Lift Axle Suspension System, for example, offers a 13.5k capacity and a 17.5-in. package size. It also features a Super Chamber lift that provides a four-second lift speed while the position provides increased protection from road hazards and easier access for servicing.
“An empty or lightly loaded tractor has the ability to operate as a 4×2, a configuration which eliminates the rolling resistance of the forward drive axle, as well as thrust and tandem scrub,” said Dave McCleave, director of marketing at Hendrickson Truck Commercial Vehicle Systems, which offers a liftable forward tandem axle. The OPTIMAAX system is designed to automatically lift the forward axle in the tandem when loads are light and shift the unsprung weight to the rear drive axle without axle overloading to provide improved traction capability.
“In the lifted position, at minimum, an additional 2% fuel economy improvement is gained, resulting in over a 5% improvement compared to 6×4 configurations,” McCleave explained. “When rolling resistance, thrust and tandem scrub is removed by having the forward tandem axle in the lifted position when the capacity is not required, powertrain components are not working as hard. This plays a part in the overall fuel efficiency gains for the vehicle.
When spec’ing lift axles, it’s important to pay strict attention to the suspension spacing.
“Federal Bridge laws established standardized axle weights and spacing on Interstate highways but they did not standardize axle weights and spacing in off-road and vocational applications,” Heath said. “The fleet manager or end user spec’ing the truck would benefit by asking the local vocational truck dealer. They will know the local weight laws and will be able to optimize the lift axle configuration to achieve the user’s goals.”
Heath went on to explain that local weight laws vary. “In some states, you are allowed to use multiple lift axles to increase your allowable Gross Vehicle Weight Rating (GWVR) and increase payloads. In others, there are limitations to the allowable number and spacing,” he continued. “In some states, multiple 8,000-lb. capacity lift axles are allowed on dump trucks. The ‘Super Dump’ is a fairly common spec in some states that optimizes the number of lift axles, axle spacing, capacity and uses the best product model to reduce overall vehicle weight and maximize payload.”