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Chapter 20: On-Road Hauling
November 1, 2007 By: Pit and Quarry Staff Pit & QuarryIf your aggregates operation is in the market for an on-road truck, such as a rear-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.
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The first thing you will need to find out is 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 Co., 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 jobsites.
Loading and hauling questions
Some key questions need to be answered concerning 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 related to the environment or roads you are operating in. Are you going to spend a lot of time on very rough jobsites 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," Lindgren said. "But if you 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."
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Drivetrain
One of the big mistakes many people make with dump-truck engines is they spec too much power, said Lindgren. "You should get just enough horsepower to do the job. Generally, 350 to 400 hp is plenty for most applications. Extra horsepower just uses more fuel, put 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 lb. 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 jobsite 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 more than 90,000 lb., you should consider an 18-speed because you get much closer splits from bottom to top."
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