There are three primary purposes of a suspension in a work truck. These purposes are:

Support the load — the suspension needs to be durable enough to handle the work expected of it.

Provide stability so the vehicle can traverse uneven and sometimes treacherous terrain without allowing the vehicle to tip.

Cushion the ride to protect the equipment, the cargo and provide for optimal driver comfort.

“Selecting the best suspension for the job relies heavily on what the application and duty cycle of the vehicle is,” according to Sean Whitfield, director of marketing for Hendrickson Truck Commercial Vehicle Systems.

For instance, a vocational vehicle used in rugged off-road conditions on worksites will require a different type of suspension than an on-highway vehicle that spends most of its time on paved streets or interstates.

“Vocational trucks require durability, stability, and traction while an on-highway vehicle will require an optimal ride condition. The keys are to spec the right equipment for the job,” Whitfield said.

Suspension Types by Truck Class

Medium-duty vehicles (Class 5-7) are, for the largest part, single drive axle (4x2 or 4x4) configurations.

“These vehicles are most often equipped with mechanical, steel leaf spring suspensions such as Hendrickson’s HTS suspension, but when used in ride sensitive applications, air suspensions such as Hendrickson’s HAS or PRIMAAX EX are also available. A steel spring mechanical suspension will be the most economical solution and will provide better stability but, in most cases, will be heavier and will deliver a stiffer/rougher ride when compared to an air suspension,” Whitfield said.

Typically, mechanical suspensions will be found in applications such as utility, dump, or box van.

According to Whitfield, the air suspension will be lighter and will deliver a smoother ride but will be higher in cost and typically require more maintenance than a mechanical suspension.

“Air suspensions can often be found in applications such as food and beverage, moving van or other applications where optimal ride quality is desired to protect the cargo,” Whitfield said.

Heavy-duty vehicles (Class 8) are most often tandem drive axle (6x4) configurations.“These vehicles can utilize mechanical steel spring suspensions, mechanical elastomeric (rubber) spring suspensions, or air suspensions. Again, the suspension choice is greatly dependent upon the vehicle’s application,” Whitfield noted.

For the most part, on-highway vehicles used primarily to haul freight on highways and interstates utilize mostly air suspensions, which provide the smoothest ride and lower maintenance.

Vocational trucks, however, incorporate a variety based on the requirements of the application.

“Applications that are not as concerned with ride quality or weight efficiency but need to be more cost-effective would be more likely to use steel spring mechanical suspensions. This could include vocations such as construction, utility, or mining. Vehicles used in more weight and ride-sensitive applications where traction and durability are still needed, such as refuse, mixer, or dump, would be well suited for an elastomeric (rubber) spring suspension.

Whitfield noted that, in both cases, steel spring and rubber spring configurations, equalizing (walking) beam suspensions are the most common and effective for providing optimal stability, mobility, and traction.

Lastly, specific jobs lend themselves better to air suspensions in the vocational world.

“These would be commonly seen in logging, oil field, heavy equipment haul, etc. In these applications, the vehicles may regularly venture off paved roads to do the dirty work so they require a high level of durability and stability, but they also will spend a significant amount of time on the highway where the smoother ride is beneficial. These suspensions tend to be a little more expensive, but the benefits certainly pay off,” Whitfield said.