Suspensions: Tuned to the job

Fleet owners enjoy the best of both worlds. They can spec out trucks and trailers to within an inch of their sanity if they so choose or they can order many vehicles “pre-engineered” for even very specific vocational niches. So it should be no surprise that even the seldom-sung suspension has become a hotbed of advanced engineering — enabling all sorts of fleets to gain performance by having a key vehicle system more finely tuned to the job at hand.

All major truck and trailer suspension makers provide products customized to specific applications; and some even make them for specific vehicles.

Among the latest examples of the latter trend is the Haulmaax lightweight truck suspension just rolled out by Hendrickson Truck Suspension Systems. Hendrickson partnered on the Haulmaax with Paccar, parent of Kenworth and Peterbilt, and the suspension will be available on new truck orders through the dealer networks of those two OEMs exclusively.

According to Sean Coleman, marketing manager for Hendrickson Truck Suspension Systems, the key advantage of the Haulmaax is that it weighs less to allow increased payload yet uses high-strength materials and advanced manufacturing techniques to ensure durability.

“Haulmaax uses an innovative spring geometry that couples natural rubber with a high-density thermoset material for the preferred ride and handling characteristics desired in construction, refuse, logging and other heavy-duty applications. It adjusts to the load, providing excellent ride quality and loaded stability.”

Coleman explains that this variable-rate spring system helps cushion the driver while protecting the cab, chassis and body equipment from vibration and harshness.

As for weight savings, he reports the Haulmaax can provide “over 500 lb. of additional payload in comparison to competitive steel-spring suspensions.”

Things are happening on the trailer side of the business as well, according to John Morgan, product manager for Hendrickson Trailer Suspension Systems. “Niche or specialized suspensions products that are adapted to specific vocational vehicles are becoming more available,” says Morgan. An indicator of this trend he points to is a food-service product. “Hendrickson's Ramp-Ready Slider,” Morgan explains, “is a slider box that's modified to hold a ramp for van trailers that must be unloaded where there are no loading docks.”

Another example from Hendrickson is the “extreme duty” Intraax 300 air-ride 30,000-lb. suspension-axle-brake package rolled out earlier this year. “It's a heavy-duty, very robust suspension system for quite severe use, such as on mining or other off-road trucks,” Morgan explains. “We're seeing a lot of interest in this product in areas, including overseas, where traditionally only heavy-duty spring suspensions were used.”

According to Morgan, Hendrickson has also taken some of the extra-duty features of the Intraax 300 and made them optional on other more “mainstream” suspensions. These include very high-dampening “rear-oriented” shock absorbers for applications encountering rough roads or high centers of gravity and a “rebound limiter” chain-down stop option that limits downward motion to avoid premature wear.

Morgan says to look for the “trailer-suspension interface” to continue to be a major focus of engineering efforts. “The more we can tie the design of the suspension into the design of the trailer, the more we can impact things such as vehicle weight,” he explains. “We expect our next-generation suspensions will both weigh less and be easier for trailer builders to install.”

ArvinMeritor is focusing its RideStar suspension line on both high-volume trailers and specialty vehicles, reports Bob Zirlin, director of worldwide marketing-suspension systems & trailer products.

“We entered the North American trailer market in '97 with our RHP highway-parallelogram suspension for sliding tandem vans,” Zirlin points out. “The RHP is very application-specific. Since it doesn't use trailing arms, the axles go straight up and down. That eliminates dock-walk without the need for add-on devices and eliminates suspension-induced backslap to give the driver a better ride.”

Zirlin says reducing backslap also appeals to vocational trailer operators. However,” he points out, “vocational fleets need a different design approach to ensure weight savings from the suspension. What we did for them with our FS fabricated suspension was develop a way to minimize backslap within a trailing-arm suspension.”

According to Zirlin, three critical aspects of the FS work together to reduce backslap and improve ride: a unique patent-pending bushing-with-shims design; incorporation of high-dampening Gabriel shock absorbers; and close attention to suspension geometry. He notes the result is a suspension that provides exceptional ride quality, stability and durability for such specialized trailers as flatbeds, tankers, and lowboys. The first model, the FS230 Top Mount, will be followed by additional units designed for various other trailer types.

ArvinMeritor also has a suspension program for tractors in development, says Zirlin. “A lot of truck OEMs manufacture their own suspensions,” he notes, “But opportunities exist in niche markets for suppliers like us.”

No matter the type of equipment, Zirlin lists the key trends in suspension development as continued emphasis on ride quality to help counter the driver shortage; engineering for lower maintenance costs; and more emphasis on developing suspension systems tuned to both the tractor and trailer.

Wayne Powell, director of marketing for Tuthill Transport Technologies, producers of ReycoGranning suspensions, says the requirements of over-the-road and vocational trailers are quite distinct.

“On the air-ride side,” Powell relates, “we offer several different designs that meet specific industry needs. The typical van with slider requires a lightweight suspension with good ride quality. To attain that, we optimize air-spring size and placement. On the other hand, roll stability is not as crucial with vans but it certainly is with vocational trailers such as tankers.”

Powell also points out a fundamental difference between vans and vocational units. “Specialized trailers may represent a 20- to 30-year investment to a fleet,” he explains, “so concern about long-term durability and overall longevity will affect how the suspension is designed. Vocational operators also want ease of service over that 20-plus year life. And, of course, roll stability to help prevent rollovers is a critical design factor.”

Yet other distinctions must be made for suspensions going on trailers that see some off-road use. “Strength is important in the on/off-highway market,” Powell says, “as is suspension travel to allow for easier maneuvering over rough and rutted roads.”

Powell says that ReycoGranning air-ride suspensions are aimed at highway applications while its steel-spring suspensions can be sued in both on- and off-highway vehicles. “There's more of an application range with steel springs,” he notes, “especially when it comes to equipping a truck or tractor.”