Suspending the Stress

When Mark McClymonds talks about stress, it's usually not the kind that can be managed by taking two aspirins and calling his doctor in the morning. As president of McClymonds Supply & Transit Co., a 50-year old family-owned bulk and aggregate hauler based Portersville, PA, McClymonds worries about the impact of stress from off-road operations on his vehicles and on his drivers. The truck's suspension

When Mark McClymonds talks about stress, it's usually not the kind that can be managed by taking two aspirins and calling his doctor in the morning. As president of McClymonds Supply & Transit Co., a 50-year old family-owned bulk and aggregate hauler based Portersville, PA, McClymonds worries about the impact of stress from off-road operations on his vehicles and on his drivers. The truck's suspension is the component critical to managing both those areas of stress, he points out.

“When you're picking up or dumping a load of gravel, all that bouncing around a vehicle does at the work site can create a huge maintenance problem,” he says.

The other element involves driver comfort. “It's a very relevant issue because if you can't get a driver to stay in the truck, what good does saving money on a particular suspension package do you?” he says.

“Ride is increasingly at the top of the list for a lot of vocational fleets because it lowers the wear and tear on their equipment, thus lowering maintenance, and also helps them hold on to that ever-scarcer component: the driver,” adds Ray Paradis, director of vocational sales for Peterbilt Motors Co.

For those reasons, McClymonds specs suspensions based on the following factors: payload capacity, life cycle value — especially in terms of maintenance — and ride comfort. “That's why the up-front cost of the suspension isn't the major consideration; it's what the suspension will give us in terms of increased payload, reduced maintenance for the vehicle, and driver retention that matters most.”


Experts see a slowly developing shift in the vocational market towards greater use of rubber block and air suspension packages as fleets search for ways to better manage the stress on vehicles and drivers.

According to Sean Coleman, marketing manager for Hendrickson Truck Suspensions, whether or not a fleet moves in this direction depends on two factors: specific application and geographical location.

Coleman points to concrete mixer fleets as an example. “About 90% of that market operates on rubber block suspensions because they are looking for [vehicle] stability, with ride quality a distant second.”

He also notes that while ride quality may be a distant second to stability in choosing a suspension system for concrete mixers, there was a time when it would not even have made the list. But that has changed as fleets try to extend the life cycles of their equipment and reduce driver turnover.

“Front-discharge mixers are a good example of this trend,” Coleman notes. “They've been one of the early adopters of rear air suspension for two reasons: there's a lot of valuable machinery on the rear of the vehicle that an air suspension can help protect from vibration and road stress, and it gives drivers a better ride without compromising stability.”

In the dump truck market, however, the shift to rubber block and air suspensions can be attributed primarily to geography. Coleman points out that the mainstay of the dump market remains the steel spring suspension because durability is so important. “In the Northeast, in particular, durability is the biggest issue [which is why] steel springs remain the top seller.”

According to Hendrickson, block and air suspensions have gained ground over the last five years, particularly in flatter areas like Arizona, where light weight and ride and handling are becoming more important.

Coleman says that ride and handling have gained in importance as the components on mixer, dump, and refuse trucks have become more complex. “For example, many refuse vehicles now come equipped with side- and rear-view camera systems to improve driver visibility,” he points out. “Ride harshness and vehicle vibration can have a major impact on those kinds of sensitive electronic systems.”


The issue of ride and handling may be growing in importance for mixer and dump truck fleets, but durability and stability are still the primary concerns. Consequently, makers of steel spring suspensions are fine-tuning their packages to give customers more options, says Michael Brown, special project engineer for suspensions at Mack Trucks.

“There are a lot of issues to deal with,” he says. “There's the issue of weight savings versus durability: How can we use lighter weight components, such as aluminum, as an option to lighten the suspension so it can haul more payload, yet not affect its durability? We're also trying to get a smoother, lighter ride for the driver, so we're offering more multileaf and taperleaf spring suspension options.”

Brown says that the traditional “camelback” design of steel spring suspensions makes them extremely durable. “It's a low-tech yet low-stress design made to absorb punishment.”

Makers of steel spring suspensions are not ignoring ride quality, however. “It's a huge focus for us as comfort and ride translate into driver retention for vocational fleets,” says Stephen Ginter, vocational product marketing manager for Mack Trucks.

As part of that, Mack is also bringing the cab suspension into the picture, Brown adds. “You can't just talk about the vehicle suspension without talking about the cab, too,” he says. “Improving the cab suspension helps isolate more of the road shock a driver feels, yet keeps the durability of the steel spring package in place.”


Auxiliary axles are also playing a bigger role in the vocational market because they can enable fleets to haul more payload, yet remain road legal.

Phoenix-based Heritage Trucking, for example, is using factory-installed Watson & Chalin Tru-Track Super Lite steerable lift axles on its Kenworth T800 super-18 dump trucks, which are equipped with 18.6-ft. dump boxes that can carry 22 cu. yd., or about 25.5 tons, of payload, according to Pete Tode, the fleet's owner.

“We get paid by the ton,” Tode says. “By going with the lightweight lift axles, we're saving over 1,000 lb. per truck and gaining that much in payload over our competition. We like the lightweight lift axles because our trucks travel up to 45 miles on the highway carrying asphalt and then go off-road to the job site. The 17.5-in. tires on the lift axles provide more ground clearance off-road,” he points out.

“Steerable pusher [axles] enable truck operators to keep weight down and increase payload capacity,” says Steve Gilligan, Kenworth's general marketing manager. “Customers can also benefit from the reduced stress on the frame and chassis, as well as reduced tire scrubbing, provided by a steerable lift axle suspension.”

Yet Garry Mans, division applications engineering manager for Peterbilt, notes that with any auxiliary axle package, payload management can't be ignored. “When you are hauling 80,000 lb., that load doesn't disappear when you raise the lift axles and drive off-road,” he warns. “Like anything else, there will be a huge impact on vehicle longevity if it's used improperly.”

“All of those issues affect the vehicle's life cycle cost and the return on investment a vocational fleet is going to expect from that equipment,” says Paul Dobson, ArvinMeritor's senior marketing manager for vocational suspensions.

“This is a rough environment,” he emphasizes. “The key is not to view the suspension in isolation, but to try and optimize the total truck picture to get all the attributes vocational fleets want.”

Payload & productivity

One of the biggest challenges facing vocational fleets today is productivity--how to haul more payload and generate more revenue, while staying in compliance with bridge and road weight laws. That's no simple task. Just ask Jeff Sutton, president of family-owned Sutton Trucking.

His Archie, MO-based fleet has to comply with no fewer than four sets of weight rules: federal limits on the interstate, state restrictions in Missouri and Kansas, and municipal laws that apply to a commercial zone spanning a 15-mile radius around Kansas City.

Sutton worked with its dealer, MHC Kenworth in Kansas City, to create a W900S “Super 16” dump truck equipped with six axles: a set-forward steer, two steerable pushers, tandem drives, and a load-bearing booster axle that swings down from the dump bed to the pavement on two hydraulic arms. The result is an outer bridge of 35 ft., 6 in. and an allowable 75,500 lb. GVW under the federal bridge law.

“With all the axles on the ground, the Super 16 dump lets us scale almost 24.5 tons of payload,” Sutton says. “That way, you don't have to send two trucks out when one will do.” He notes that his Super 16 basically does the same job as a tractor hauling a 40-ft. frameless end-dump trailer, which scales at a little more than 25 tons of payload.

“As a dump operator, we're constantly looking for new ways to work more efficiently and profitably,” Sutton explains. “When you show up on a job hauling six, seven, or maybe 10 more tons than the trucks those other guys are using, that's what makes customers happy and keeps them calling back.”

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