Spec suspension for trouble-free performance
Sure, today’s heavy-duty suspension systems are fairly trouble free. But, any suspension system, whether on a truck, tractor, dolly or trailer, is going to give you trouble if you try using it outside its design parameters or simply ignore routine maintenance.
Spec for the application
Even when it seems that you’ve thought of everything when you write your specs, you can run into problems.
“If you’re using a trailer suspension with a 23,000-pound capacity in a logging operation, chances are it’s not going to last very long,” says Ken Griswold, trailer suspension systems product manager for The Holland Group. “You may load the trailer to capacity with nice dry logs, but before making a delivery, run through a storm where the logs absorb rainwater and you could experience a significant load increase. Such situations can quickly tear up equipment. You can compound the problem even more if you need to go off road.”
Facing such a possibility, a fleet manager might well consider spec’ing a heavier suspension, but over-spec’ing should be done cautiously for either air or steel suspensions.
“For air suspensions, too often, there’s a belief that if 23,000 pounds is good, 25,000 must be better, even though the suspension will never carry 25,000 pounds,” says Wayne Powell, director of marketing at Reyco Granning Suspensions. “The result is that the air spring will always carry less air for which it was designed.”
With regard to a vocational truck with steel springs, Powell says it’s important to know the weight it will carry.
“Over-spec’ing will cause an unnecessarily rough ride,” he says. “Under-spec’ing can result in spring breakage, sag or sway.”
It may even be desirable to consider spec’ing a suspension with dissimilar springs for some vocational applications. Consider, for example, a fire engine that has a water tank installed on one side or bucket truck with a heavy digger-derrick mounted off center.
“Air can be very helpful in such a situation because height control valves on each side can compensate for a side-to-side unbalanced load,” Powell says.
Fred McKee, power train sales manager at Mack Trucks says, “Common problems resulting in component failures can sometimes be caused by misapplication, either from initial spec’ing errors or changes in a fleet’s operation. Initial spec’ing can be quite precise with the software programs now available, but we must thoroughly understand the true application requirements and spec the truck accordingly, not just which components are the lightest weight or least expensive. Changes in a fleet’s operation are sometimes difficult or impossible to foresee. With the wide variety of options available, along with the ability to spec to a specific application, changing the application becomes more difficult and costly.”
ArvinMeritor’s Russell Franks says, “In general, understanding the vehicle’s vocation and application is key. Using the standard suspension may not always be the proper choice, even though standard equipment tends to be the most weight and cost efficient due to the competitive nature of today’s market. Contacting the OEM and discussing the overall application and vocation of equipment being specified is the best way to proceed in the beginning. These are people with the expertise to review application requirements and help specify equipment best suited for a specific need.”
An understanding of a truck’s expected application is particularly important when writing specs for vocational operations. “An off-highway application with high articulation requirements would suit a ‘walking beam’ rear suspension to maintain traction in the high articulation environment,” says Ben Smith, chassis engineering manager at Freightliner.
Tracey Maynor, Great Dane’s vice president of branch sales and operations, echoes how good specs depend on a thorough understanding of the future application of a trailer saying “A variety of factors needs to be considered – all components of application and environment. The fleet needs to know the trailer’s:
• intended use;
• region of the country;
• condition of the roads where it will operate;
• load requirements;
• frequency/load cycle;
• how often the trailer is dropped and hooked;
• whether it is loaded with a truck under it or unhooked;
• the type of product to be hauled;
• required dock height;
• whether dock walk is an issue; and
• how the trailer is loaded (by hand, forklift or clamp machines).”
Continual improvement
Equipment has definitely improved in recent years. Timothy Fulkerson, technical service specialist for the Commercial Vehicle Systems group at Dana Corp., says, “Thankfully, better suspension suppliers of today are doing a good job from an engineering standpoint in designing and making highly robust systems. Still, we do see occasional problems occurring that are related to really bad road conditions, especially concrete roads with bad joints and a lot of holes. When you’re constantly subjecting your suspension to this type of operating environment, shocks, air springs, hangers, even tires, are going to experience premature wear. Road debris can also cause an inordinate amount of harm. We’ve seen situations where debris and tire blowouts have hit and interfered with air springs to such an extent that they have slashed and punctured the air springs.”
System failures are becoming more and more rare, thanks again to the robust designs of today’s suspensions. There are, however, still complications related to cold winter months when air lines get contaminated. This can bring about a host of problems, including ride height control valves that can leave the suspension in a deflated position and issues with brake valves that can result in dragging, if not inoperable, brakes.
“Fleet managers need to know operational factors, such as the intended application, percentage of off-highway use, engine torque requirements, load capacity and GCW/GVW requirements,” says John Burch, on-highway segment manager at Hendrickson Truck Suspension Systems. “In addition, peripheral items having a direct effect on suspension performance, such as auxiliary axles, tire chains, axle spacing, plows and cranes, among others, must all be taken into account when spec’ing a vehicle’s suspension.”
Even when making a decision regarding air versus mechanical suspensions, an understanding of the application also is critical.
“Like any component, an operator should consider a series of questions, which address how the trailer should be spec’ed,” says Bob Zirlin, director of marketing for trailer products at ArvinMeritor. “For example, what kind of trailer will be used (flatbed, van, reefer, etc.)? What will the trailer haul? How important is ride quality? How important is price? How long will you keep the trailer? How much maintenance is the operator willing to perform? What trailer floor height is required? All these questions should be reviewed before making the decision to spec an air suspension.
“It’s important to remember that suspensions have far-reaching effects on the trailer, from legal load, stability, steering and braking to height of the body,” he says. “In addition, the trailer suspension can positively affect cost for fuel, tires, fines and the driver’s well being. Many fleets are specifying air suspensions because they are seen as an investment in better, more productive equipment. With new technologies being increasingly specified to increase the speed and efficiency of the tractor, such as electronically controlled, high-torque/low-RPM engines, an increased amount of stress and torsional vibrations are being experienced by the rest of the vehicle. In addition, importance is being placed on equipment that can maintain the increased speed of the vehicle. Air suspensions can reduce vibrations and protect the cargo and trailer equipment, while being able to keep the trailer stable and provide soft riding at increased speed. Vocations that are operated in off-highway applications, such as loggers, cement trucks and dump trucks, are also finding value in air suspensions. The one segment that still seems satisfied with mechanical or spring suspensions is LTL carriers.”
Mike White, vice president of sales at Hutchens Industries, says, “Fleet managers must consider the vocation of the vehicle they’re spec’ing and decide whether their needs are best served by an air suspension or a leaf spring suspension. The differences in cost, weight and durability can be significant. One size shoe does not fit every foot!”
Dana’s Fulkerson notes, “As air ride suspensions become more and more popular, we’re starting to see some misapplication issues. Fleet managers need to understand what will work and what won’t work. For example, they need to know that a 40,000-pound line-haul suspension isn’t designed for extra-heavy hauling or off-highway applications. That type of expertise comes with experience. Conversely, problems begin when you have someone with little or no experience, and that person specs something that just isn’t appropriate for the application. It comes down to being familiar with your specific application and what suspensions are out there today to handle those applications.”
Take care of it
There is, of course, more than the original price that must be considered when the cost of owning any component is calculated.
“When calculating life-cycle costs, fleet managers need to consider the importance of key suspension attributes like weight, ride quality, off-road mobility, torque reactivity and stability; the level of service and warranty coverage from the supplier; the availability of aftermarket parts; and maintenance requirements of the suspension,” says Hendrickson’s Burch.
According to ArvinMeritor’s Franks, “Pneumatic and electronic issues tend to be the most common problem items today. Within air suspensions, items like air bags, shock absorbers and pneumatic valves are most likely to be issues at some time in the life of the equipment. Mechanical suspensions tend to have issues with cracked leaf springs and structural damage due to higher load inputs being seen by the equipment.
“In general, maintenance being performed will be thorough on things understood and minimal or not at all on things that are not understood,” Franks says. “Having proper training by system suppliers should always be a goal for a maintenance staff. Along with this, today’s long-haul driver tends not to inspect or service equipment as well or regularly as does a driver in a short-haul operation. Training these drivers to perform basic visual inspections, along with regular scheduled service, will help find small issues before they become big problems.”
Dana’s Tim Fulkerson echoes the importance of a trained driver, saying, “Your best ally in suspension maintenance is the driver – an experienced driver with a sharp eye and the knowledge to look for potential problem areas. Too often, you’ll see a situation where the driver pulls into a truck stop, gets out and goes about his business without even looking at the truck. That’s just asking for trouble.
“On the other hand, a good driver will always be on the lookout for anything abnormal and spot a potential problem before it develops into something serious. A lot of problems can be avoided with routine inspections. A simple walk-around can be one of your best defenses in preventing downtime related to a suspension.
“We’ve also found that the use of a checklist can be a very effective maintenance tool. That checklist should include a visual inspection of key suspension components, including air springs and shocks; air and electrical lines; suspension components, like hangers, brackets, fasteners, bushings; and structural components, along with brakes and wheel ends.”
Mack Truck’s McKee says, “Improper, incomplete or lack of maintenance continues to be a major issue for fleet managers. Technician and driver training can go a long way to prevent or minimize subsequent failures. Most suspension failures can be prevented with proper maintenance, periodic inspections, ride height adjustment, wheel alignment, retorquing of fasteners and dump valve operation, etc. Fleet managers need to be aware that wheel and axle alignments become critical with the new stability control systems.”
Bruce Barton, director of engineering at the Ridewell Corp., says fasteners represent the single most common item in need of maintenance on suspensions, and the first re-torquing is the most critical.
It seems like a good idea to keep Hutchens Industries’ White’s advice regarding suspension maintenance: “It’s the same as it was when I started in this industry 42 years ago – Keep the bolts tight!”
