Spec'ing Dump Trucks

Brian Lindgren, vocational market sales director for Kenworth Truck Company, offers advice

If you're in the market for a dump truck, it's important to do your homework. Unlike some other vocations, dump truck specifications are very regionalized. What works in one area of the country will not work in another.

Your first piece of homework: Find out what the length and weight regulations are in your state. Try to take maximum advantage of the weight laws to maximize payload. Some states (mostly in the West) require compliance with the Federal Bridge Formula; others don't. This will have a big influence on how the axles are set up and spaced.

"A Bridge Formula truck will tend to be longer to spread the weight," said Brian Lindgren, vocational market sales director for Kenworth Truck Company in Kirkland, Wash. "You may need to have lift axles, but there are different rules on how much load you can add with lift axles. And some states don't allow pusher axles. Your dealer should know the rules and regulations."

In states where you don't need to comply with the Bridge Formula, you can spec trucks shorter and heavier, making them more maneuverable on job sites.

Some key questions that need to be answered concern the loads that you expect to haul. For example, you will need a different chassis spec when hauling bulk loads such as asphalt, sand or gravel than you would if you hauled mostly demolition debris.

If you're planning on visiting a lot of demolition sites, you will need to have the body and suspension beefed up to handle the pounding it will take from the large pieces going in the dump body. Your body supplier will have input on this.

The hauling question is related to the environment or roads you are operating in. Are you going to spend a lot of time on very rough job sites, or will most of the hauling be long distances on smooth gravel and sealed roads?

"If you will be going off-road a lot into rough terrain, you'll need a suspension that is heavier duty and has more articulation," Kenworth's Lindgren advises. "But if you'll be hauling longer distances, you'll need to consider the trade-off between the ease of dumping and the ability to haul more load per trip. For example, a transfer dump will allow you to haul more with one driver, but it will take longer to unload. Double bottom-trailers carry a lot of payload, too, but with those you're limited on where you can drop the load — it's a lot harder to dump gravel into a hole for a swimming pool, for instance, with bottom dumps."

One of the big mistakes many people make with dump truck engines is they spec too much power, says Lindgren. "You should get just enough horsepower to do the job. Generally, 350 to 400 horsepower is plenty for most applications. Extra horsepower just uses more fuel, puts more strain on the rest of the drivetrain, and adds cost up front.

"If you go with a smaller 12-liter block, you save around 700 pounds over a 14- or 15-liter block," Lindgren said.

The transmission put behind the engine needs a lot of ratio range. You need a low enough gear to get out of a hilly job site and high enough top gear to attain decent highway speeds. The Eaton Fuller 8LL transmission is a common truck spec, but he suggested an 18-speed transmission for larger and heavier trucks. "The 8LL gives you two low gears for startability off-road and enough top-end range for the highway," said Kenworth's Lindgren. "But if you are hauling over 90,000 pounds, you should consider an 18-speed because you get much closer splits from bottom to top."

The typical dump truck uses rear axles rated at 46,000 pounds. This covers most trucks, from 14/16-yard solo dumps through combinations up to 110,000 GCW.

Lindgren says the rear axle ratios should be matched with the transmission so that engine speed is around 1,600 rpm at highway speed. He recommends side-to-side differential locks for traction.

Another thing to remember for operating off-road is air filtration. Lots of drivers love the look of dual polished external air cleaners, and these provide excellent filtration with low air restriction. But they are quite expensive compared with under-hood air cleaners. If you are purchase-price conscious, go with an underhood filter with a pre-cleaner to remove large particles and much of the dust before it ever reaches a filter. "A little money spent up front on a better air cleaner is cheap compared to a dusted engine." And better filtration will usually mean longer life for the filter elements. For example, dual 15-inch air cleaners will last over seven times as long as a single 11-inch underhood air cleaner before needing replacement.

If you are hauling a lot of loads per day, cutting vehicle weight can be profitable. You can slim down by spec'ing components — such as wheels, air tanks and clutch housings — in aluminum rather than steel. "Use the smallest fuel tank you can get away with," Lindgren added. "Some operators can get away with a 56-gallon tank, but most will need at least 75 to 90 gallons to get through a day."

You can also save valuable pounds by choosing the right suspension. "The difference can be as high as 400 pounds," Lindgren says of the different suspension options.

To avoid hauling around extra steel in the vehicle frame, have the dealer work with a Kenworth application engineer so that you only get enough frame where you need it. You will typically need an extra strong crossmember at the back of the cab to strengthen the hoist-mounting area. If you are planning to add lift axles later, make sure the dealer adds that information to the order so that the frame can be prepared for them.

But remember that many of these weight savers will cost more up front. You will need to balance that against the gains you expect to make hauling more payload.

Finally, let's look at a few driver performance-related items. To get the best turn performance and road feel from steering, Lindgren recommends dual small gears rather than a large single steering gear. The dual system will also last longer than a single system.

Try to spec as much glass area as possible. Lindgren also suggests picking low-replacement cost windshields when they are available. "Most vocational fleets replace at least one windshield side per truck per year. Two-piece flat-glass windshields with roped-in seals can be replaced in half an hour for a total cost of under a hundred dollars. This can save thousands of dollars over the life of the truck."

With lift axles, it's smart to get a six-channel ABS system. "Lift axles, especially steerable ones, are normally over-braked for the load," Lindgren says. "By including them in the ABS system, they're less likely to lock up and you reduce tire flat spotting."