Class 8 dump trucks

Heavy-duty dump truck productivity is dependent on many factors, but ultimately easy to ascertain. If a truck is properly equipped for the application at hand, staged correctly once it’s on a jobsite, leaves with a full load and returns quickly for another, odds are it’s making you money.

A good dump truck operation depends on a maddening array of variables: terrain type, size and type of equipment on site, material being loaded, haul road conditions and length of haul to the dump site vary widely by job, or even by the day.

People can also have a huge impact on loading operations: Having an experienced, capable foreman can do a lot toward alleviating idle trucks or equipment. Veteran machine operators can quickly fill truck beds in the fewest number of passes possible to keep jobsite congestion at a minimum. Good drivers make a difference, too. Owners know seasoned drivers are priceless when it comes to getting fully laden trucks out of a hole, up a grade or through heavy traffic. Drivers can save you money by operating the truck in a fuel-efficient manner, or they can literally send your profits up their exhaust stacks in a puff of diesel smoke.

All of these challenges may seem daunting to the uninitiated. But luckily, creating a smooth-flowing dump truck operation usually boils down to old-fashioned common sense. In most cases, logjams are easy to identify and correct. If additional resources are available, foremen can accelerate an earthmoving operation by routing more equipment and trucks to a slow area to speed up the excavation process and reduce truck idle times. Rental options make replacing low-volume machines with higher productivity units easier than ever before.

And of course technology is playing its ever-present role. Recent advances in commercial satellite tracking technology and advanced communication systems mean even lowly dump trucks will operate on a just-in-time arrival model akin to those found in ready-mix and parcel delivery applications today.

Low-emission engines drive up prices
But a good dump truck operation begins with the truck and the spec’ing process that creates it. For many years this process remained fairly constant for owners. Typical payload, terrain type, haul lengths and equipment reach requirements yielded a formula that owners could depend on to give them the production and profits they desired. Personal preferences, such as a desire for high horsepower or improved fuel economy also came into play, and allowed owners to custom tailor trucks perfectly matched to their job and business model.

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The spec’ing process remains an integral part of the North American truck industry today, and will continue to be important for many years to come. But the playing field is changing, truck manufacturers say. Recent technological advances, the increasingly difficult problem of finding qualified drivers and – most notably – the changes wrought by the federally-mandated low-emission diesel engines introduced in 2002 are altering the way trucks are being spec’d forever.

“Today’s engines run most efficiently at lower revs than earlier diesels,” says Brian Lindgren, vocational sales director, Kenworth. “The new low-emission engines have to be run between 1,400- and 1,600 rpm, instead of 1,900- to-2,100 rpm as most folks are used to. This not only means the driver needs to be re-trained, but often the transmission and axles ratios might need to changed to optimize power and fuel efficiency at the new, lower rpms.”

“Vocational trucks are really being hit hard by the new low-emission engines,” says Jim Crowcroft, manager, product planning, Sterling Trucks. “They are causing serious design problems with the trucks. All these engines – whether they use EGR or ACERT technology – drive additional heat rejection back into the engine. And that is not desirable. It’s causing us to put bigger radiators in the trucks for a given horsepower figure. Those radiators, in turn, give us big challenges with vehicle packaging and the ability to offer certain vocational features that these trucks need – features like frame extensions, deep wheel cuts and front PTO systems. And all these problems and the solutions we have to create to defeat them drive a lot more cost into the truck.”

And those rising costs aren’t only found on the front end of a truck purchase, either. Fuel economy and horsepower figures for the new engines are also down, although the decrease wasn’t as bad as many industry experts initially predicted.

Mark McClymonds, president, McClymonds Supply & Transit, Portersville, Pennsylvania, runs Peterbilt and Mack dump trucks through the hills of western Pennsylvania. His parents started the company in 1945. When he bought them out in 1983 his fleet totaled four dump trucks. Today his fleet numbers more than 260, including several new trucks equipped with post-’02 diesel engines. “We’re seeing a little bit lower mileage from the new engines,” he concedes. “But it’s not an alarming decrease. On the good side of the equation, we haven’t seen any maintenance issues arise yet, and the new engines seem to be just as durable as the units they replaced.”

Look at your bottom line numbers when spec’ing horsepower. If you can’t quantify the increased power with increased production, go with a less powerful engine.

Contractor says changes ensure low-emission productivity
McClymonds says he typically specs Caterpillar C12 and Mack ASET diesels in his new trucks. He’s always been a believer in high horsepower, which he feels his drivers need in order to negotiate the hilly terrain. “Our data tells us we lose a half mile per gallon running the bigger engines,” McClymonds notes. “That’s an operating expense we’re willing to accept in order to have the reserve power on hand to get our trucks up the steep hills in this area. In addition, we only keep our trucks for five years. And you get better resell value for used trucks if they have the big engines under the hood.”

McClymonds specs a Cat 435-horsepower engine in his daycabs and straight trucks. “We only run about a 100- to 200-mile radius from our headquarters,” he says. “If we go out 250 miles, that’s a long haul for us.” Still, the need for longer distance travel is there, so McClymonds maintains a number of trucks with sleeper cabs. Those trucks are spec’d with a Cat 475-horsepower engine since they spend more time on the highway.

Although McClymonds has opted to keep putting high-horsepower engines in his trucks, Crowcroft says many contractors may begin to question the value of putting big block engines in their dump trucks. “A contractor who used to spec a 350-horsepower C12 or Mercedes 4000 engine needs to stop and consider those additional costs and ask themselves how bad they really need that 350 horsepower. The new price structure means your old formulas aren’t going to hold true anymore and it’s time to consider other options. Maybe you can go with a 350-horsepower, small-block engine. Or maybe you can go to a 330- or even a 300-horsepower engine in a small block and still get your work done.”

When calculating horsepower, Crowcroft says his personal rule of thumb is pretty straightforward: 300 horsepower will move 80,000 pounds up a point-and-a-half grade. “I’ve held that rule in my heart for many years,” he says. “And the math still holds true today – low-emission engine or not. But you can get the job down with less horsepower. It may not get done in the most attractive manner. And it may be annoying as hell to your driver. But it can be done.

But reality says you need to have reserve horsepower. And in some parts of the country you need a lot of reserve horsepower. In the Rocky Mountains, a 300-horsepower engine isn’t going to get you very far. And even less dramatic terrain plays a role in shaping your powertrain configuration. “If you get into a hilly state like Virginia, you need both high horsepower and torque,” says Ray Paradis, vocational trucks product manager, Peterbilt. “But if you’re running in the flatlands of Florida, then horsepower is not that big of a deal. You can shift your focus then toward spec’ing a powertrain with an emphasis on low-end torque.”

If you’re not sure how much horsepower to spec for your dump trucks, Steve Ginter, vocational product manager, Mack Trucks, suggests examining the cycle times your trucks make. “Horsepower is an investment and costs you money at the fuel pump,” he says. “So you need to make sure you’re getting value for it. Look at your average trip cycle times and try to determine if additional horsepower is going to gain you any productivity. If you’re getting seven cycles a day out of a truck with a 300-horsepower engine, can you get eight or nine cycles – without violating posted speed limits – from a truck with a 350-horsepower engine? If so, you can probably justify the extra power.”

But if that experiment is successful, Ginter says, don’t assume that even more horsepower will send your productivity skyrocketing. “If you’re moving up or down on the horsepower scale, I’d strongly recommend doing so in increments,” he says.

Powertrain torque a better indicator of potential productivity
Horsepower is an important component in spec’ing any dump truck, but manufacturers caution it is not the single most important factor. “Most times when a truck is off road, it’s torque you’re looking for,” says Bill Sixsmith, director of marketing, severe service trucks, International Truck and Engine. “Remember that torque gets you going and horsepower keeps you going.”

Horsepower is vital for highway tractors to go 70 or 80 mph, Sixsmith points out. But depending on your typical haul lengths, odds are your dump truck driver is going to top out around 55 mph on his trips back and forth from the jobsite. “But when your trucks are off road, how fast do they go?” he asks. “The top speed is probably around 15 or 20 mph. And once the bed is full, the truck needs to have the available power handy to pull out of loading sites or to climb a grade out of an excavation pit.”

That said, it’s important to note that spec’ing and deploying a dump truck with too much horsepower can also cost you productivity in a myriad of ways. The most obvious consequence is increased fuel costs. But Ginter says other problems can crop up as well. “The increased weight of a big-bore engine can hurt the truck’s gross cargo weight rating, sometimes by as much as 250 pounds,” he says. “You might also see unexpected maintenance problems. All the extra power goes straight to a truck’s powertrain, which may not be configured to handle it properly. You might find your trucks are starting to snap axle shafts in mud. That’s a controlled failure to avoid catastrophic damage to the driveline, but it’s also a sign that you’ve got too much power under your hood.”

Ginter says the same principles apply with transmission. “You need low gear ratios to effectively work off road,” he notes. “But you have to be careful when matching big engines with those transmissions since all that extra power will be immediately transferred to the transmission and could result in premature failures.”

If you insist on putting big-bore engines under the hoods of your trucks, Ginter says it’s best to spec engines and transmissions with torque-limiting capabilities for protection from sudden horsepower surges and to limit premature component failures.

Although fuel consumption is marginally higher, McClymonds Supply & Transit has encountered no major problems running low-emission Cat and Mack diesels in its fleet this year.

Consider spec’ing low-ratio transmissions as an alternative
Transmission gear ratios are important for good dump truck productivity, and can also be used to solve other problems as well. McClymonds, for example, says he’s started spec’ing lower gear ratios for all his new trucks with low-emission diesel engines. These lower ratios, he says, keep the engines running slower and help them run cooler – always a concern with their increased heat rejection properties.

What kind of difference can a low-ratio transmission make? “Consider that a 335-horsepower engine with 1,550 torque and a low-ratio powertrain will do the same work as a 380-horsepower engine will. You want as low a gear reduction in your dump trucks as possible,” Sixsmith stresses. “And this is true for both forward and reverse low gears. That’s why Eaton’s Double-L series of vocational transmissions are so popular. They give you a lot of drivability with a big 14/8-bottom end and double overdrive at the top. So you’ve got the flexibility of increased ratios at the bottom end and still have a good top end speed.”

The problem there, both manufacturers and contractors alike say, is that the old Gear Jammers of yore are becoming increasingly hard to find. That’s why many feel automatic transmissions will be the next Big Thing to hit vocational truck applications – including dump trucks in the next few years. “I’m looking for automatics to come on big time,” says Paradis. “I think that in the next five years, upwards of 50 percent of the transmissions being spec’d for vocational trucks will feature some sort of automation system. Experienced drivers are getting harder to find. And it’s much easier to get an inexperienced driver – including growing numbers of women drivers – up to speed in a truck with an automatic transmission.”

“We don’t have any automatics in our fleet yet, but I think they’re an interesting concept for dump trucks,” McClymonds says. “We don’t run out of people that can shift gears, we run out of people that are qualified to drive. By that I mean finding people who meet our qualifications in terms of experience and a clean record. So I don’t see that automatics would open that up for us. But they might open the door for making new hires if they have no experience.”