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Suspensions specifics

When it comes to specifying suspension systems fleets need to consider weight, uptime and application. But today’s more sophisticated systems may be able to offer more.



When it comes to specifying suspension systems fleets need to consider weight, uptime and application. But today’s more sophisticated systems may be able to offer more.

Ensure best performance

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According to Steve Miller, chief engineer, CVS, Arvin Meritor, “When I think of getting the best performance from a suspension system, I think of increased payload and trailer uptime. There has been more usage of lighter weight materials on the undercarriage to allow carriers to increase their payload. There is increased use of sensors on the undercarriage to aid in identifying preventive maintenance items to try to keep trailer downtime to a minimum. Roll stability controls are becoming more common to aid in preventing trailer rollovers. Con-trols on the undercarriage to help prevent damage to the trailer and/or undercarriage are becoming more common.

For fleets specifying the right suspension for a better ride, and more effectively protect cargo, Miller says, “Many of the trailers are being loaded with varying cargo from one day to the next. One day they may be loaded to the legal limit, the next day they may be running lightly loaded. The operating environment of the trailer needs to be considered when selecting the correct suspension for a given application. A dedicated-haul trailer can have a suspension tailored to a specific need where a general-haul trailer needs a suspension with more adaptability. A suspension that is too stiff in a lightly loaded trailer can result in a harsh ride potentially damaging the cargo, trailer or other components. A suspension that is too soft on a heavier load can result in the suspension bottoming out, causing higher loads into the cargo bay and potentially damaging the cargo, trailer or other components.


As for the right suspension and good suspension maintenance practices adding life to tires and other components, Miller says, “In addition to maintaining proper tire inflation, it is also true that proper axle alignment and properly working shock absorbers affect tire and component life. When it comes to axle alignment, the alignment of the axle to the king pin is important for the trailer to track properly, but proper axle-to-axle alignment will have the bigger effect on tire wear. The end user needs to inspect shock absorbers per the manufacturer’s recommendation to ensure that the components are continuing to perform as intended. Properly working shock absorbers can result in less fatigue damage and improved tire life. Additionally, fleets need to ensure they are operating the suspension system within the suspension and axle manufacturer’s recommended parameters, such as proper load based on the suspension and axle rating, operating at the correct ride height, etc.”

Miller goes on to say, “The integrated product is being developed as a system rather than individual components and, as a result, the interface points can be optimized to achieve the best performance. The optimized product in many cases isn’t just in the product design, but in the manufacturing process which in many cases incorporates robotic welding.”


Performance features

Hendrickson notes that tapered beam and large-diameter axle (LDA) applications represent two emerging technologies that not only enhance performance, but also reduce weight. It teams the two technologies for Advanced Axle/ Beam Technology (AXT).

With tapered beams, INTRAAX, VANTRAAX and the all-new QUAANTUM suspension systems put structural strength where it needs to be and keep the weight to a minimum, reports Scott Fulton, on-highway program manager for Hendrickson Trailer Suspension Systems.

New bushing compounds and manufacturing processes help narrow bushings outperform prior models. An optimal frame bracket footprint creates a more robust attachment to the trailer. Large-diameter axles increase strength and stiffness but still trim weight. Straighter and stiffer LDA means better tire life. Reducing weight improves fuel efficiency and provides haulers with the ability to increase payload.

Fulton says that other advances in technology include automatic tire inflation systems, such as Hendrickson’s TIREMAAX, which help keep tires properly inflated. A popular option, TIREMAAX detects and responds to low tire pressure by directing air from the trailer air tank to one or more tires when the inflation pressure dips below a pre-set level. With an ultra-rugged rotary connection the system is warranted for up to seven years. Long-life wheel ends such as Hendrickson Unitized System (HUS) with up to a seven-year warranty ensure years of worry-free service.


Fulton goes on to say, “Certainly, specify air-ride for the best ride. An air-ride suspension uses a height control valve to create the best ride quality based on the payload on the trailer. An integrated suspension is the best choice because all the components have been designed to function together as a system.”

For example in a true integrated system, the axle, air springs, shocks, bushings, and brakes work in harmony to provide the best ride and cargo protection. Components specified independently can be far less effective. To make sure the springs and shock absorbers will be most effective in protecting the cargo and trailer, haulers should also be sure the specified suspension is tailored for the type of trailer and load it will carry – not a one-size fits all design.

When asked how the right suspension and good suspension maintenance practices can add life to tires and other components, Fulton responds, “With a properly maintained suspension, the tires are kept in contact with the road leading to better performance and longer life. Ensuring proper tire inflation and axle alignment represent two of the best ways to add life to your tires. TIREMAAX automatically helps ensure tires run at the proper pressure, and QUIK-ALIGN provides a simple and efficient method to align trailer axles in the event an adjustment is required.”


Keeping the suspension well maintained protects not only the cargo, but the trailer structure as well. Components such as lights, door hinges and even walls and the roof last longer because they have less exposure to vibration and damaging impacts.

Some suspension integration systems can improve performance. Fulton says that better durability – by robotically controlling welds during manufacturing, INTRAAX and VANTRAAX ensure precise fabrication methods and the best quality controls in the industry. Tight controls result in elevated

performance and reliability. These benefits are not possible unless parts are designed and manufactured as a system.

With a system approach, the manufacturer designs every piece to work specifically with every other piece. Fleets and owner operators receive components with exacting fit, meaning they function precisely as planned. Ultimately, that leads to better performance.

“In non-integrated suspensions, parts must maintain compatibility with a wide range of other components – that invariably leads to design compromise,” Fulton says. “Additionally, manufacturing practices and environments may vary widely with designs comprised of many independent pieces.”

He goes on to say that by designing the brakes as part of an overall system rather than as separate components, haulers receive the best stopping performance and reliability. In addition, features like the integrated cam tube system cut down on required maintenance by holding more grease, and facilitate easier maintenance by allowing the S-cam to be serviced without removing the hub. A shorter S-cam means less wind-up and more responsive braking power. These im-provements are a result of making the brakes an integral part of the INTRAAX system.


Lighter weight – complete integrated suspension systems such as INTRAAX and VANTRAAX optimize weight savings by allowing the use of advanced manufacturing methods and thinner and stronger materials, Fulton adds.

Uptime, cost control

According to Bill Hicks, SAF-HOLLAND, “Fleets need equipment that is going to maximize uptime and reduce the cost of ownership. The company has introduced new technologies that prolong suspension life and greatly reduce downtime. New bushing technology, for example, in SAF-HOLLAND’s new CB2300 and CB4000 greatly extends bushing life. Hicks says Holland’s SwingAlign is the industry’s most advanced axle alignment system, which allows fleet to align axles in a fraction of the time.

When specifying suspension the right one for the job will provide a better ride, and more effectively protect cargo. Hicks notes that suspensions are design for specific loads and applications. Fleets not familiar with the spec’ing process are advised to seek application assistance from the OEMs or suspension manufacturers.

He goes on to say that the right suspension and good maintenance practices add to the whole system. The proper suspension selection and maintenance program will enhance the overall suspension system and trailer field service life by:


• Greatly reducing or mitigating (absorbing) road shock inputs. These inputs can cause premature failures of electrical components (lights, electrical connections and wiring) as well as failure of mechanical components such as hinges, floor cross members, king pins, and slider sub-frame and rails, for example.

• Maintaining proper tire alignment – proper selection insures the right suspension system design to handle the loads and maintain axle alignment during most service needs. The ability to quickly adjust axle alignment, made possible with such features as Holland’s SwingAlign, is another key factor in easily maintaining the correct axle alignment specs as frequently as the fleet may require. Periodic inspection and corrective maintenance of any connection hardware in the suspension system that needs replacement will also extend the life of the tires as well as other suspension components such as frame brackets and equalizing beams.

Hicks goes on to say that systems integration can improve performance by optimizing the interface between critical components. In short, integration is an engineering approach that assures compatibility within the system – as a result the system’s performance is enhanced.

Spec for cargo

Ted Solida, Triangle Suspension Systems Inc. Flagg Suspension Product manager, says “Knowing what type cargo you are hauling over 70 percent of the time should determine what type of suspension you spec on your trailer fleet. If you were hauling non-fragile products such as apparel or footwear you would spec differently than when hauling electronics or glass products. The first scenario could lead to spec’ing a lower cost leaf spring trailer suspension, but in the second, more than likely, you would be looking at an air ride type of suspension to protect your cargo.


“This would also be true if you were running a $300,000 stainless steel pressurized tanker to haul liquid nitrogen or LP gas. From the standpoint of a better ride it makes sense to try and match up your tractor’s type of suspension with your trailers, air-ride on the tractor and air-ride on the trailer. Fortunately the tractor air-ride will mate well with both the mechanical suspension and an air suspension.”

He goes on to say that, again, based on what the vocation or the type of cargo being hauled, it would be wise to spec the trailer with the appropriate suspension, air for fragile loads, and mechanical where breakage is not an issue.

Solida notes that some suspension integration systems have improved performance. He says, “The biggest change has been the automatic air pressure regulators for the trailers. This will maintain air pressure to the tires, which in turn lengthens the life of the tires.”

Maintenance tips

Arvin Meritor’s Miller, says, “There are many different types of suspension systems so it is difficult to generalize on maintenance tips. Most, if not all, suspension manufacturers have recommended in-spection, maintenance and replacement frequencies outlined for their products. Adhering to these recommendations will optimize the performance and life of the suspension system. The first step is remembering the trailer is an important part of the revenue cycle, so don’t ignore it!”


Hendrickson’s Fulton says, “One key element in air-ride system maintenance is to make sure suspensions are set to the proper ride height. Never operate a vehicle without air in the air springs. Keep the air spring pistons free of dirt and debris and keep the areas around each air spring clear of other vehicle components or items that can contact the rubber air spring bellows.

For shock absorbers, conduct periodic visual inspections looking for damaged mounts and bushings, damaged dust covers or bodies, bent or dented shocks and oil leakage. Shocks may have some typical oil misting around the seal area resulting from normal operation; however, if a shock absorber is found to be actually leaking oil in streams, it should be replaced.

As a part of routine maintenance, visually examine all trailer pivot connections by looking up at the bushing tube from under the trailer. Specifically inspect the voids and metal cores for separation and excessive settling.

SAF-HOLLAND’s Hicks says, “ The big three (but by no means the only three) suspension maintenance concerns are:

  1. First and foremost, the suspension’s ride height must be checked/verified per specification.
  2. Next, a visual inspection of all suspension components should be performed looking for any obvious signs of undue wear or road debris damage that could be an early indication of trouble.
  3. Third, the major fasteners utilized, such as the pivot connection or axle attachment (if utilized), should be confirmed.

Triangle’s Solida suggests including tire maintenance in your suspension maintenance program, “To protect tires, make sure that all of the shocks are in good working condition, make sure the suspension and steering components are greased on a regular time frame according to the truck manufacturer’s specifications and when greasing king pins and tie rod ends make sure to take the weight off the axle so you can purge all or most of the old grease.


“Check suspension pivot bushings for sign of wear or side to side movement. If this is movement is allowed to go on for an extended amount of time not only will you need suspension work done you will also need to replace one or more tires,” he says.

In the future

Arvin Meritor’s Miller says “There continues to be a push for increasing the payload so we will see further use of alternate materials, such as composites. Additionally, we could see the trend to more effectively integrate the suspension into the trailer structure to eliminate re-dundant materials at the interface points and to enhance the performance of the product. With fleets looking to optimize trailer up-time, we should also expect to see an increased usage of electronic controls and sensors.”

Hendrickson’s Fulton says that in the future there will be even more systematization – expect to see options such as hubs, bearings and tire inflation systems becoming more integrated into complete optimized suspension packages.

Improved performance monitoring – tracking status of tire pressure, remaining brake life and wheel bearing integrity, will be incorporated into future systems.

SAF-HOLLAND’s Hicks says that for the future, the industry can expect a continued evolution of systems technology augmented by advancement in cost reducing features. Tomorrow’s suspension will be easier to maintain and provide an easier ride for both the driver and cargo.


Other future suspension system improvements include rack and pinion steering, says Triangle’s Solida, which he says will become an option along with braking and steering by wire.


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