Shaken and Stirred

Freightliner LLC began offering air front suspensions a few years ago says Frick, who explains that technically, these are a combination of steel spring and air and now represent a large portion of Freightliner LLC's line haul build rate. "Although current suspensions are a combination of spring and air, we expect that these will transition to full air suspensions," he says.

Freightliner LLC's most recent introduction is in axle suspensions—a monoleaf style spring front suspension, which is expanded across the Freightliner Trucks and Sterling product lines. The monoleaf suspension is designed to reduce friction in the spring to improve the ride and reduce weight by having fewer leaves than those found in multileaf suspensions. This technology is now standard in the 8,000-, 10,000-, and 12,000-lb. front suspensions in the highway truck category, where the ride and weight improvements are best realized. According to Frick, Freightliner LLC is the first to offer this system in a front suspension in North America.

Over at Hendrickson, Nash says his drivetrain background gets him excited over the new HTB, which is a heavy-duty, on-highway air suspension that is non-torque reactive like it's off-highway cousin, the PRIMAAX. The big benefit with the HTB is it is very light in weight due to aluminum used in construction. The HTB also has a torque box, which takes the place of torque rods, but it works the same and requires less maintenance according to Nash.

Frick explains that while technology exists for front and rear active suspensions, his company does not see the payback for the customer with these products in the near future. Citing initial cost along with potential complexity, they feel that it will be a number of years before these suspensions are prevalent. Similarly, independent front suspensions, while gaining popularity in motor home and other rear-engine applications, Freightliner expects that it will be at least another generation of highway trucks before independent front becomes a factor in a forward engine chassis.

"Space requirements and structural requirements on a forward engine chassis make application of an independent front extremely challenging," says Frick. "The day will come, but not in the near future."