Optimize. That's the mantra experts chant when you ask them how to lengthen the life of a waste-collection truck's tires and brakes.
Optimizing means taking into account the application for which the truck will be used, selecting a chassis appropriate to that application, then specifying tires and brakes appropriate to that chassis.Because some tradeoffs among competing goals often are necessary, an optimal truck may not be ideal in every respect, but it will operate efficiently and cost-effectively throughout its useful life.
Cutting corners on chassis design (which includes the frame, axles, suspension, and transmission), payload capacity, horsepower, or anything else will compromise the truck's overall performance in ways that adversely affect tire and brake life and performance. So will overspecifying, which seems paradoxical but can make a difference if you choose components with a higher performance rating—and cost—than the job actually requires. Either way, even the best tires and brakes that money can buy won't meet performance and useful-life expectations on a truck that isn't right for the job.
Optimizing is easier to say than to do. An involved process that's both science and art, it takes into account a host of variables to define a suitable truck for a given set of circumstances. Then comes the task of choosing from among the many technologies, brands, and models on the market today.
Four Value Drivers
One perspective on optimizing comes from Steve Kiefer, director of marketing and program management for Hendrickson International, a suspension manufacturer. Based in Woodridge, IL, Hendrickson is a subsidiary of The Boler Company of Itasca, IL.
Kiefer lists four "key value drivers" that guide all of his firm's product-development activities:
- Reducing the cost of ownership for the vehicle's whole life cycle. "Larger fleets in particular are very financially oriented and value driven," he says.
- Reducing the vehicle's weight. "Operational efficiency is foremost for many fleets," he says. "Increasing their ability to carry more payload and reducing overload tickets means more dollars."
- Improving ride. "Ride has two major benefits," Kiefer notes. "It enhances driver satisfaction and reduces fatigue, and it also ties into the cost of ownership by reducing damage to the chassis and the body. Bodies have become more sophisticated, with electronics and hydraulics that require a smoother ride."
- Improved traction, which comes from an increase in articulation—the extent to which the individual axles in a tandem assembly can move freely up and down, independent of each other, to maintain the traction that keeps both axles driving. Otherwise one axle could get hung up on an obstruction and lose traction. A severe-duty suspension that maximizes articulation and traction is especially important for vehicles operating on rough roads and in landfills, but could constitute an unwarranted additional expense for a waste-collection vehicle that runs only on city streets and empties its load at a transfer station.
More Variables
Other variables include geography, route characteristics, federal and state weight limits, the preferences and priorities of the people buying the truck, and the needs of the people who will use the truck day after day. So where do you begin?
Start with the gross vehicle weight (GVW), which is the vehicle plus its load, advises Scott Edelbach, director of sales and marketing, refuse division, for McNeilus Companies Inc. of Dodge Center, MN, a body manufacturer. McNeilus is a subsidiary of Oshkosh Truck Corporation of Oshkosh, WI.
"Figure out how heavy a payload combination you're going to carry," Edelbach advises. "Then have axles adequate to carry that load, then suspensions adequate to carry the axles, then brakes and tires, then the engine and transmission.
"You can do a lot with a small engine and transmission if you're on a flat surface and won't go over 45 miles per hour. You'll need a bigger engine and transmission if you have 6% or 7% mountain grades, or if you have a long ride to the landfill and want to drive 65 miles per hour because that's the speed limit. Then consider seating capacity, and whether you need air conditioning."
Other considerations include steerability and maneuverability. A tight turning radius may be desirable in cramped quarters, but with greater wheel cut (how far off of center the wheel can turn) comes more tire scrub, a major factor in tire wear. Wheel cut ranges from 34 degrees on some older trucks to 55 degrees on some of the latest models.
When a truck makes a tight turn, the rear axle becomes a pivot point for the whole chassis. As a truck with a dual-wheel tandem drive turns left, all eight tires pivot around the inside left tire on the lead axle. Skidding and sliding, they rub off the rubber. Additional tire wear is the price an operator will pay for faster maneuvering through the route.
Tire size also figures in this equation. Smaller tires allow greater wheel cuts where a larger tire might turn into the frame or the cab. As manufacturers build better tires with a higher GVW rating, a smaller tire may be able to do a job that previously required a larger one. "The 315 tire previously was rated at 9,000 pounds, but now it's rated at 10,000 pounds. You can use it in situations where, before, you needed to go up to the 385 tire, which is 1.5 inches wider and could affect turnability," Edelbach says.
Body Style
How all these variables enter into the choice between the rearloader, frontloader, or sideloader body style for an MSW collection fleet illustrates the complexities of optimization.
Traditional rearloading packer trucks comprise 45% of all municipal waste-collection bodies in the United States, reports Houston Ratledge, production manager at body manufacturer Heil Environmental Industries Ltd. in Chattanooga, TN. Heil is a subsidiary of New York City–based Dover Corporation Inc.
"Rearloaders are the most antiquated, but still the most utilized in the industry—and they're still being made and bought," Ratledge says. "They span the entire spectrum from the smallest city to the largest conglomerate. They range in payload from 6 cubic yards to 32 cubic yards, with compaction ratios from 500 pounds per cubic yard to 1,300 pounds per cubic yard. In terms of chassis configuration, they range from two axles—steering and driving—to five—steering, tandem, pusher, and tag."
Ratledge says the most popular payload size for a rearloader is 20 cubic yards, in part because it mounts on a single rear axle, helping minimize maintenance and repair costs. Second in popularity is 25 cubic yards, even though it mounts on a tandem axle, which is inherently harder on tires. The third most popular, 32 cubic yards, is used primarily where the landfill is remote from the collection route, so the operator needs to go to the landfill with the largest possible load.
As a general rule, Ratledge says, "The smaller the town, the smaller the truck, but Philadelphia and Boston need small bodies to go down narrow alleys. The older the city, the more difficulty a larger truck will have negotiating its inner-city routes."
Efficient but Unappreciated
The frontloader has a carry can that can hold the refuse from seven to 10 homes at a time before being hoisted to discharge its load into the hopper. Some have a cart tipper mounted on the carry can.
Frontloaders are slowly becoming more popular, Ratledge says. "It's a very efficient system, but people have failed to appreciate its merits. It has captured 90% of the restaurant business, 6% or 7% of light industrial, but only 3% or 4% of the residential market."
Ratledge concedes that frontloaders can be hard on streets. "They're heavy, big, difficult to turn, and can't get around some cul-de-sacs without backing up three or four times," he says.
Pricey but Productive
The automated sideloader, with a mechanical arm that grasps, hoists, and tips a tapered cart to empty its contents, "is by far the most efficient system in the industry and the most productive on a cost-per-home basis," Ratledge says. It's a one-man operation, with no helpers aboard to be unproductive when it goes to the landfill. The driver-operator stays in the truck except where a handicapped resident needs help, so personal-injury and liability exposure are low.
"It's also best from a load-distribution standpoint," Ratledge says. "A typical automated sideloader will load the front axle to about 18,000 pounds and the rear axle to about 36,000 pounds. A balanced axle-load distribution is much easier to achieve." That makes the suspension requirements for a sideloader less exacting and more forgiving.
Ratledge says an automated sideloader for a given application will cost about 20% more to purchase and maintain than a rearloader, but will pay for itself by reducing personnel costs and by nearly doubling the route efficiency in collections per hour. Whereas a rearloader on an average route may service 70 homes per hour, an automated sideloader should be able to service 120 homes per hour—or more. "I ran a route in Phoenix that did a pick every 22 seconds," he says. That's 163 homes per hour!
A sideloader's frequent starting and stopping puts extra stress on its brakes and tires, accounting for much of the sideloader's higher maintenance cost. "It doesn't matter," Ratledge says. "When you look at the bottom line, in dollars and cents you have a net benefit."
Getting the Weight Down
Given a GVW dictated by operational requirements or federal and state weight limits, reducing the chassis weight yields greater payload. Weight issues apply to all body styles, but because frontloaders tend to be heavier, their operators are especially eager to trim pounds. "In California, where weight regulations are strictly enforced, some frontloader operators shooting for the absolute very lowest weight are running trucks with phenolic [plastic] materials and aluminum chassis frames," Ratledge says.
Truck manufacturers are responding wherever possible by using lightweight composite materials, aluminum parts, and ductile iron.
Mack Trucks Inc. of Allentown, PA, a member of the Volvo Group of Gothenburg, Sweden, recently introduced its new Advantage chassis series, which allows a user to choose the best frame-rail size and strength for a specific application. It comes in four rail sizes—6-, 7-, 8-, and 9.5-millimeter. All have a higher resistance bending moment (RBM) than Mack's pre-existing line of rails. Tom Davis, Mack's marketing manager for highway products, notes that the new 7-millimeter rail has a higher RBM than the current 8-millimeter rail, but is up to 100 pounds lighter.
"For customers requiring a very heavy-duty rail who to date have been opting for our 6-millimeter with quarter-inch inside channel reinforcement, the new 9.5-millimeter is an excellent alternative. Not only is it lighter, but it also eliminates the need for an inner channel, which prevents potential corrosion from occurring in this area," Davis says.
Suspension Selection
The purpose of a suspension is to connect the tires to the chassis, and to cushion the shock that the tires transmit from the road. Three main types of suspension exist: mechanical, rubber, and air. Each has proponents and detractors. Some firms specialize in just one type; others—including Hendrickson and Ridewell Corporation of Springfield, MO—offer diverse lines in an effort to satisfy multiple preferences and needs. Hybrids combining two different suspension types also are available.
In the beginning, all suspensions were mechanical, a direct bolting of axle to frame. Then steel leaf springs were introduced to absorb some of the bumps and jolts. Leaf springs are well known for strength, stability, and traction, but they're relatively rigid. When you hit a pothole, the truck tends to rattle.
In older models with extremely rigid steel leaf springs, cornering sharply at high speed could create flat spots on the tires because they would hop (leave the pavement). In extreme cases, an axle could break when the truck's weight came down on it after a hop, resulting in a costly repair job.
Extreme rigidity also becomes a problem when a purchaser overspecifies because he expects to overload the rear axles and wants the same margin of overload protection in front. "Bigger is not always better," Kiefer counsels. "If you have a rearloader with a conventional cab [as opposed to cab-over-engine] and a 12,000-pound to 14,000-pound payload on the front axle, choosing a 20,000-pound front-axle suspension isn't good. A 20,000-pound suspension is designed to flex when it gets to 20,000 pounds. If the payload rarely gets there, the suspension has no give. The truck will ride incredibly hard, which is rough on the driver, and the vibration in the cab will shake the dashboard apart."
Among the many mechanical suspensions available today, the new Mack Advantage chassis has a standard front taper leaf suspension with new taper leaf springs spaced slightly apart to reduce friction, and a reduced spring rate to soften the ride.
Mack's widely used camelback suspension is a stacked spring set that is durable but heavy. Volvo's T-ride suspension weighs less and has fewer springs, which are longer and less rigid, better able to flex and absorb road vibrations.
Hendrickson's R Series products, which have evolved over more than 75 years, feature steel leaf springs and a walking beam that connects the forward and rear axles. The walking beam sets up a pivot point between the axles, allowing them to move independently so each axle can maintain high traction.
Rubber's Pros and Cons
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| The Watson & Chalin 13000 Suspension |
Advocates of rubber suspension claim it reduces weight, improves the ride, and represents the lowest life-cycle cost solution. Detractors contend that it's durable but unforgiving. "When Heil mounts a body on solid rubber," Ratledge says, "we put a special reinforcement on the underside of the body. A rubber suspension is so harsh that it imposes high stress loads on the steel componentry of the body, so we have to reinforce it to keep it from failing."
Some rubber suspensions are in fact a combination of steel and rubber. Hendrickson makes suspensions with multiple rubber blocks spaced on steel suspension brackets to absorb the shock. Chalmers Suspensions International of Mississauga, ON, Canada, sets a large rubber puck in the center of a steel mounting.
Kiefer says Hendrickson's HAULMAAX suspension—a walking beam suspension with rubber springs—is "becoming the real workhorse of the refuse industry. It reduces vibration into the body, electronics, and hydraulics. It's the lightest leading suspension for collection vehicles, at least 300 pounds lighter than a steel suspension, and it requires no lubrication for the life of the vehicle."
At WasteExpo in Dallas in May 2004, Autocar LLC of Hagerstown, IN, a wholly owned subsidiary of Grand Vehicle Works Holdings LLC of Highland Park, IL, announced that it was making HAULMAAX its standard lowest-cost suspension offering, rather than a $500 option.
Ridewell's Dynalastic rubber elastomer spring suspension is an independent torque-beam equalizing suspension for a tandem drive configuration. Bruce C. Barton, Ridewell's director of engineering, says the lead axle and trailing axle are connected to the suspension pedestal with independent arms so the axles can articulate independently, and they evenly divide the load between the lead and trailing axles.
Dynalastic, he says, is well suited to rearloading waste-collection trucks and is on several thousand New York City sanitation-department vehicles. "It's durable and low-maintenance, on a par with leaf spring suspensions. Rubber block suspensions are typically rough riding, but we can tune these elastomer springs for near-air-spring ride quality."
To provide roll stiffness, Dynalastic has a lateral control arm that runs from atop the axle housing to the chassis frame-rail member. "It's a very stable suspension in cornering and for vehicles with a high center of gravity," Barton says. "In addition to the four main rubber springs on a tandem suspension, there are four overload springs. As more capacity is needed, the overload springs come into play."
The overload springs provide a 15%–30% redundancy ratio for consistent overloading without seriously affecting the durability of the suspension, and an extreme safety factor of 2.5 to 1 based on the yield strength of the materials used in the suspension.
Auxiliary Rubber Springs
Timbren Industries Inc. of Ajax, ON, makes Aeon Hollow Rubber Springs. They can be installed at the factory or as a retrofit to supplement a vehicle's primary suspension system. Edwin C. Sanders, Timbren's national sales manager, describes a classic waste management scenario:
"If you operate in areas with rough, potholed roads, you're constantly breaking springs. We've talked with waste management people who were so over budget in maintenance that they would never budget extra money upfront to save themselves money in the long run. They just keep replacing springs.
"Some forward-thinking managers, however, will specify our product on their fleet and save themselves spring damage. Our rubber springs cycle at a different rate than steel springs, so when you hit a pothole, the energy is absorbed into the rubber, sparing the steel."
Sanders says his firm's springs also enhance roll stiffness by about 12%. Sideloaders in particular are prone to having loads heavier on one side than the other. "We can level that load," Sanders says.
In communities where waste-collection trucks do double duty for snow removal, Sanders says, "We can help them carry a side-wing plow, without beefing up the right front spring, by using a rubber spring. We supply a half kit for one side of the truck."
If the use of rubber springs raises ride-quality issues, they can be resolved, Sanders says, by reformulating the rubber to change its internal structure and hardness, and by repositioning the springs so they engage more or less aggressively.
If positioned properly, Timbren's rubber springs also improve braking performance, especially for trucks with disc brakes and parabolic springs. When the brakes engage, the front axle tends to twist as the tires stop rotating. Sanders says placing rubber auxiliary springs behind the axle helps prevent this phenomenon.
On recycling vehicles, which are relatively light and stop and start constantly, the axle can twist in one direction when stopping and the opposite direction when starting. "To correct this," he says, "we put rubber springs fore and aft of the front or rear axle, or both."
Still another benefit of Timbren's rubber springs is reduction in axle hop and rear-tire wear when trucks run empty coming back from the landfill, Sanders says.
Floating on Air
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| Ridewell's 225 Lift Axle |
Air suspension provides superior ride performance and driver satisfaction. Air springs get their springiness due to compression of the air inside. Because the driver can regulate the air pressure on the springs, air ride adapts well to load changes, reducing axle hop when a truck is running empty. Air springs also offer superb traction—especially in mud or snow.
"The spring rate in a leaf is a linear spring rate. You don't get extra oomph for a bump because you're already starting at a high rate," explains James A. Eckhardt, head engineer at Silent Drive Inc. of Orange City, IA. "In an air spring, the spring rate is a curve. At a bump, the spring rate is low. As the air gets compressed, the spring rate increases rapidly. This helps make the ride smoother. It's like an air pillow. You push a little bit, and it feels nice and soft; you push hard, and the harder you press, the stiffer it gets."
On the negative side, air suspension costs more to install and maintain because of its pneumatic system, with a compressor, air tank, and plumbing. It has more moving parts than a leaf suspension, may not last as long, and doesn't perform as well in the rugged environment of a landfill. "When you have a truck's rear axles dragging garbage through a landfill, the debris can puncture the air bags," notes Edelbach. "Also, air suspension is not as stable. The air pressure will shift from side to side, so taking the body up to dump its load creates an unstable platform."
Hendrickson makes two air suspension lines, PRIMAAX and AR2. PRIMAXX, Kiefer says, is ideal for transfer vehicles that run empty about half the time, and offers "optimal ride for a collection vehicle, with good stability and traction. A major midwestern city is buying PRIMAAX for its rearloaders."
AR2, introduced in 2004, combines the walking beam's traction and durability with the smooth ride of air suspension, for fleet operators who want that combination and are willing to sacrifice other attributes. For a suspension with a 46,000-pound rating, AR2 is 139 pounds heavier than the PRIMAAX air suspension, which in turn is 177 pounds heavier than HAULMAAX rubber springs. Also, AR2 costs over $1,000 more than PRIMAAX, which costs about $500 more than HAULMAAX.
Roger Elkins, product manager for The Holland Group Inc. of Holland, MI, says his firm's AD series heavy-duty drive-axle air-ride suspensions are "100% off-highway rated, and improve brake and tire life in urban areas where drivers do a lot of stops and starts."
With respect to roll stability issues, Elkins says his firm's products augment the air springs with an equalizing beam that supports the axle and a transverse beam that functions as a torsion bar, absorbing up to 80% of the roll forces. "This design allows us to use air springs in applications with a high center of gravity," he explains.
Elkins contends that the higher upfront cost of air suspension is recaptured during the first year or two of operation in improved tire and brake wear, and in reduced road-shock damage to chassis cross members, hydraulic cylinders, the battery, lights, and breakable parts of the truck.
Maintenance, while necessary, doesn't significantly increase an air suspension's life-cycle cost, he says. "Operators who specify air ride figure that for the occasional punctured spring they would rather have trucks protected with the quality of air ride. We did a study on the refuse industry and found that many operators would not use air ride where trucks are dumping directly into a landfill, but will where they are using transfer stations."
Watson & Chalin Manufacturing Inc. of McKinney, TX, also makes a severe-service air-ride suspension with a 100% off-highway rating. Rick Rickman, director of sales and marketing for Watson & Chalin, agrees that "you get back the additional cost of air ride in maintenance and the performance of the vehicle."
Auxiliary Air Suspensions
Some refuse vehicles have auxiliary axles with air suspensions. The operator lifts the auxiliary axle off the ground when the truck is unloaded, then deploys it to the ground as the load increases. Because federal and state weight laws apply on a per-axle basis, adding an auxiliary axle to a chassis increases its legal capacity and allows it to run longer routes before having to dump its load.
Ridewell's higher-capacity auxiliary axles have a trailing-arm design, which means the axle attaches to a suspension beam behind the pivot point. "A hanger bolted to the truck frame extends down and incorporates a rubber bushed pivot," Barton explains. "The suspension beam extends back from the pivot and connects to the axle. An air spring at the end of the beam isolates 60% to 65% of the shock, and the bushing absorbs the rest.
"We typically attach the auxiliary axle ahead of the lead tandem-drive axle. The higher-capacity auxiliary axles are rated up to 25,000 pounds and have considerable tire-to-ground clearance when raised."
Barton says Ridewell's product has a pair of main load springs that support the load from the axle, and a pair of lift springs used to elevate the axle. "When you lift the axle, you exhaust the air in the main springs and inflate the lift springs. To deploy the axle, it's the reverse."
Silent Drive also offers a trailing-arm auxiliary-axle design. "We sell the auxiliary axle and air-ride suspension as one unit," says Eckhardt. "Our patented Uro-flex polyurethane bushings on arms and axle seats reduce the vibration that travels up through the suspension, adding to the longevity of the axle."
A typical auxiliary axle with air suspension costs about $3,000, Eckhardt says. "Whether installing one makes sense in a given instance depends on how far the owner wants to run that truck, and how many loads he has to haul to pay for that axle before it starts making him money. If he has a short route, he may never fill up the truck."