Class 7-8 trucks: What’s best for your job?

Because there are so many powertrain, body and chassis configurations, writing a generic article about spec’ing Class 8 construction trucks can be difficult. So we’re taking a slightly different tack: We dreamed up four fictional construction trucking applications, assigned some specific, real-world needs and problems to each and then asked North American Class 8 truck manufacturers how they’d recommend tricking out a rig for each one. No matter what your application is, or where you’re running trucks, there’s advice here you can use the next time you’re spec’ing a truck for your fleet.

Western Star 4900 FA

The scenario
Type of application: Asphalt dump
Location: Northern California
Terrain type: Mix of heavy urban driving (San Francisco/Oakland) and light mountains (Napa Valley)
Typical haul times: Short (under an hour, traffic permitting)
Special considerations: California emissions regulations, severe lack of skilled drivers, Bridge Formula state

Emphasize driver comforts
This particular application is a good match for Freightliner’s M2 112 vocational dump truck, according to Jonathan Randall, director of market programs and pricing. “This truck provides all the maneuverability, visibility and payload capability both drivers and owners need for asphalt spreading and hauling operations,” he says.

“The Mercedes-Benz MBE4000 engine provides good performance at a practical price,” Randall notes. “I’d mate it to a 10-speed AutoShift automated transmission and a Mercedes engine compression and turbo brake.”

The transmission will ease the task of shifting for the unskilled drivers a contractor in this situation has to rely on, while the compression and turbo brake will enhance safety and control when they are coming down out of the mountains. For further solutions to issues, Randall suggests spec’ing a driver-side air suspension seat, a single-passenger air suspension or two-person passenger seat and powered windows and mirrors, all of which makes for a more comfortable work environment.

A six-by-four axle configuration maximizes the truck’s legal axle-load limits, Randall notes. He’d put a 12,000-pound capacity front axle on this M2, and a 40,000-pound rear unit with a Freightliner AirLiner rear suspension. “The AirLiner is affordable and features reduced overall component weight, yet it maximizes vehicle payload and driver comfort,” he says. “The AirLiner also features brake chambers on the forward side of the axles, which gives the truck excellent clearance for asphalt spreading applications.”

Good visibility, automatic transmission help inexperienced drivers
Because a Class 7 dump truck is limited to 33,000 pounds gross vehicle weight, productivity demands dictate a Class 8 truck for this California application, according to Stephan Olsen, vocational market segment manager for Kenworth.

Kenworth prides itself on producing custom-built trucks to meet specific applications. So for asphalt work, Olsen says he’d spec out the T800 with an 80,000-pound gross cargo weight transfer dump package. “Its sloped hood will give the driver increased maneuverability and visibility, both of which can save time when negotiating heavy urban traffic and congested jobsites,” Olsen explains. “The T800’s wraparound windshield and Kenworth’s proprietary

DayLite door and peeper window provide an environment that could increase the driver’s confidence and productivity – a bonus since finding and retaining drivers is a problem.” In addition, Olsen says the T800 has large, easy-to-reach grab handles and the wide, evenly spaced steps provide a comfortable path into and out of the cab – especially important for a driver who will be getting into and out of the cab dozens of times in a day.

As for the truck’s engine, Olsen thinks a minimum of 380 horsepower is required. He’d go with a unit in the 11- to 13-liter size class and top the spec out at 470 horsepower. “That’s more than adequate to handle an 80,000-pound gross cargo weight,” he says. “A larger engine would certainly provide more power, but it would be at the expense of reduced payload and decreased fuel economy.”

Normally, Olsen recommends a 10-speed deep reduction manual transmission for this type application (at minimum) to provide the necessary gear ratio coverage an asphalt dump needs.

A 13-speed gearbox would provide shorter steps between gears, he notes, allowing the driver to better manage the engine rpms to optimize performance and fuel economy. “But if faced with a lack of driver skills, an automatic transmission should be considered,” he adds. “While they do command a price premium and are significantly heavier than a manual, automatics can improve cycle times, reduce wear and tear on the drivetrain and chassis, and improve driver retention.” Although Kenworth offers cooling packages up to 1,520 square inches for demanding applications, Olsen says the company’s standard 1,200-square-inch unit will work fine in this case.

Olsen thinks a walking beam suspension is best for this application. “Vast improvements in ride quality have been made with walking beam suspensions in recent years,” he says. “They offer the best performance in terms of stability, which is important for dump trucks carrying high-center-of-gravity loads. They also articulate well, which pays off in jobsite work and traversing uneven terrain.”

California Super Dump best choice for Bay Area asphalt hauler
“Since California is extremely strict in enforcing its Bridge Formula laws, I’d suggest our 4900 FA model straight body dump truck,” says Stan Skrzypiec, product manager, Western Star Trucks. “This is our set-forward-front-axle model with a Bridge Formula setting of 29 inches from front bumper to axle and really distributes the weight evenly throughout the truck.”

Skrzypiec says Western Star customers in the Bay Area are spec’ing more Mercedes-Benz MBE 4000 engines in their trucks. “It’s a 12-liter engine, and pound for pound probably the lightest weight engine out there in that size class. And anybody hauling any type of commodity will tell you any pound saved on truck componentry is an extra pound of payload.”

At the same time, Skrzypiec says the MBE 4000’s 450-horsepower rating and 1,550 foot-pounds of available torque can easily handle the rolling hills around San Francisco.

The shortage of trained drivers calls for an Allison automatic transmission. “That’s a great transmission for unskilled drivers, but it costs more,” Skrzypiec notes. “Another option is the Eaton Ultrashift automated transmission. It delivers similar performance in a 10-speed gearbox (a 13-speed unit will debut next year) but doesn’t cost as much as a full automatic unit. Either gearbox will eliminate clutching and shifting as a driver function.”

Ordinarily, Skrzypiec says he’d put Western Star’s standard 1,350-square-inch copper/brass radiator in this truck. But if you spec an automated or automatic transmission, then a slightly larger cooling package should be used. The thinking here is that a 1,450-square-inch radiator will help keep the entire driveline cool and meet the increased heat rejection demands and stress placed on it by the automatic or automated transmission.

Skrzypiec says he’d spec either the Hendrickson Haul-Maxx or Western Star’s TuffTrac rear suspension. “They’re comparable systems,” he explains. “Although the TuffTrac is a better choice if high articulation and bumpy terrain concerns you. I’d spec Western Star’s standard 10- or 11-inch frame with sleeves over the bogie suspension for a little extra stiffness.”

Skrzypiec also recommends a California Super Dump configuration – a tandem axle with a stinger on the rear to max out the Bridge Formula payload spec. “I’d put a 20,000-pound axle on the front, and a 46,000-pound unit on the rear tandem,” he says. “Overall I’d spec a 120-inch bumper-to-back-of-cab length. This will give those inexperienced drivers more cab room, less doghouse intrusion and help lengthen the truck to help with the Bridge Formula requirements.”

The Scenario
Type of application: Aggregate, gravel and sand hauling
Location: South Florida
Terrain type: Extremely flat
Typical haul times: Long (in excess of one hour)
Special considerations: Sandy off-road conditions, trucks operate in extremely heavy traffic conditions and high temperatures in summer months.

Lightweight aluminum components, cti handle sandy soil conditions
Extensive use of aluminum components is recommended when spec’ing a truck for this application, says Steve Ginter, vocational product manager, Mack. “This application has long hauls so fuel economy is more of a concern than it would be for jobs with shorter cycle distances,” he notes. “The goal is to maximize profitability. The way to do this is to minimize the amount of fuel consumed per pound of payload. And reducing the weight of the truck is the first step. Lightweight componentry will increase fuel economy and payload and allow you to make more trips in a day.”

Mack’s Class 8 Granite is Ginter’s choice for this aggregate hauler, powered by a Mack AMI 335 diesel engine. “This contractor is in sand part of the time, so I’d be inclined to mate that engine with the Mack T-310 10-speed transmission,” he adds. “It has good startability, which would boost performance in loose sand.”

On the other hand, Ginter notes the heavy traffic this truck will routinely encounter and the flat Florida terrain makes a strong case for Allison’s RDS automatic transmission. “That transmission would be paired with Mack’s AI-375A engine,” he says, “which is specifically tuned to work optimally with Allison five- and six-speed transmissions.”

In Florida, it’s legal to run a 23,000-pound front axle, which Ginter recommends. “At Mack, that axle requires a liner on the frame for additional strength,” he says. “So I’d spec either a 3/8- or 5/16-inch frame with a 46,000-pound rear axle. My thinking here is that you’ll want to make fewer trips per day, so you’re likely maximizing your payloads.”

Ginter considers a central tire inflation (CTI) system a must for this contractor. All-wheel-drive systems, which Mack offers, are an option, Ginter says. “Many of our Florida customers spec all-wheel drive to help them through the sand,” he notes. “But it’s really better suited for pure mud. CTI is the latest technology for dealing with adverse soil conditions and it really matches well with dry or wet sand by allowing the driver to deflate the tires for added traction when required and re-inflate them once he’s back on the highway by pushing a button on the dash.”

Mack Granite

The Scenario
Type of application: Residential and commercial construction
Location: Eastern Tennessee
Terrain Type: Mountains
Typical haul times: Vary, sometimes extremely short (under 30 minutes), occasionally longer runs up to an hour in duration.
Special considerations: Jobsites are often extremely muddy; trucks have relatively long (1/2- to 1-mile) off-road hauls before transitioning to pavement.

Diff locks, severe-service cab among heavy-duty highlights
Peterbilt’s Model 357 with a 119-inch, set-forward front axle is vocational product manager Al Zwicky’s choice for this dump truck operation. “Normally I see this as either a Class 7 or 8 application, but dealing with heavy payloads in the mountainous terrain makes me lean toward the Class 8 357 Model,” he says.

Cat’s C15 ACERT diesel rated at 475 horsepower is Zwicky’s engine of choice. “We do sell some Cat C13s in that part of the country, but high horsepower engines are more popular due to the steep inclines and muddy conditions this contractor has to deal with.”

The mud and mountains also lead Zwicky to recommend the Eaton-Fuller 8LL manual transmission. “It’s got a low first gear, low gear reductions and the startability that will help the driver power through mud and get started quickly on steep inclines,” he notes.
Unfortunately, though, these terrain types are brutal on manual transmission clutches, so

Zwicky wouldn’t rule out an Allison RDS4500 automatic. “The Allison costs more up front,” he says, “but long-term operating costs are greatly reduced, as is maintenance-related downtime. There are no clutches to replace, so you will make the initial cost investment up over the life of the truck.”

Although Zwicky considered several front and rear axle combinations, he ultimately decided on 20,000-pound front and 46,000-pound rear axles with a Hendrickson automatic HMX rear suspension. “Based on the articulation needed in a muddy environment, this suspension has a good weight-to-durability ratio. Plus, it’s a maintenance-free suspension.”

Zwicky says the muck this truck would routinely work in would lead him to spec differential locks to give extra power to pull through sloppy ground conditions. “That degree of articulation combined with diff locks will get the truck out of anything,” he says.
On the frame, Zwicky would spec a 10-3/4-inch rail with an insert or full liner. “I’d recommend Peterbilt’s huck bolt fasteners as well because they’ll help prevent any frame maintenance issues and make the chassis more durable overall.”

Finally, Zwicky would recommend Peterbilt’s severe-service cab for this application. “It’s a stronger cab,” he notes. “We replace some of the higher stress aluminum components found in our regular cabs with steel for more structural strength. Any exposed surfaces are still aluminum to resist corrosion, but the added steel helps the cab withstand all the twisting and racking a truck like this would be subjected to on a daily basis.”

The LT 9513 with low-end oomph for muddy ground conditions
“This application needs a Class 8, straight body dump truck,” says Matt Wilson, product manager, heavy-duty vocational trucks, Sterling. It’s a pretty straightforward application, even though you have to deal with mud and mountains. But you ought to be able to handle both obstacles without a lot of expensive options if you spec wisely.”

Wilson recommends the Sterling LT 9513 for this application, powered by a 430-horsepower Detroit Diesel or Mercedes-Benz engine. “That’s what most of our customers in this area are running,” he explains. “Either choice is a good, high-horsepower engine capable of handling steep inclines and powering out of muddy holes.”

Wilson would mate either of those engines to Eaton-Fuller’s 8LL, 10-speed, manual transmission. “The low gearing offered by this unit would be perfect for climbing steep hills and getting through the muck,” he adds. At the same time, Wilson would spec a 4:56 rear end. “The rear end really depends on how much top speed you want for the truck,” he notes. “But in mountain country with relatively short haul cycles, I’m thinking highway speed isn’t going to be a priority. And the lower gear ratio will help you on hills and in the mud.” Despite the tough climbs uphill, Eastern Tennessee isn’t the Rockies, so rarified air isn’t a concern. For that reason, Wilson says Sterling’s standard cooling package will work fine.

Looking at the chassis, Wilson thinks Sterling’s standard frame is the best choice. He’d suggest putting a 20,000-pound front axle and a 46,000-pound rear axle on the truck, along with Sterling’s proprietary TuffTrac rear suspension system. “It’s a light-weight, durable and low-cost suspension,” he notes. “And given the off-road conditions this contractor has to deal with, I think it will provide the extra articulation he needs when he’s working in the mud and dirt.”

As far as options go, Wilson only recommends adding a steerable pusher axle to the truck. “Again, this would really help this truck deal with excessive muddy conditions and maneuvering the truck when it’s off the highway,” he says.

The scenario
Type of application: Heavy highway construction
Location: Southern Arizona (Tucson)
Terrain Type: Mostly flat, but significant mountain terrain is a possibility
Typical haul times: Long (over an hour)
Special considerations: Severe summer heat, high dust and abrasion levels, lots of rock hauling (heavier than normal loads)

VHD with pusher or booster axle to meet Arizona bridge laws
Volvo’s VHD six-by-four straight body dump truck is Volvo product applications manager Mike Cantwell’s choice for heavy-duty construction work in the Arizona desert. To meet Arizona Bridge Formula Laws, he’d spec the truck with a set-forward front axle with a 20,000-pound front and 46,000-pound rear axle.

“I’d be tempted to suggest a pusher axle as well,” he adds. “This truck could be fitted with either a 16- or 18-foot dump box. If the contractor specs the 18-foot box to maximize his payload, he can also spec a booster axle mounted on its rear section. If he doesn’t spec the booster axle, he’ll need the pusher axle to give him a little more carrying capacity by spreading the truck’s load out more between the front and rear axles.” Either axle configuration, Cantwell notes, will keep the truck in line with state laws.

Under the VHD’s hood, Cantwell says he’d spec Volvo’s 435-horsepower VED12 diesel engine. “This engine is used around the world in all sorts of harsh environments,” he notes. “It’s actually extensively tested in Arizona to meet hot weather conditions. So it would work well for this application.” Cantwell notes that the VED12 is available in several horsepower ratings, but he opted for the 435 version to give good low-end torque and the power necessary to deal with any mountainous terrain you might encounter.

The T-Ride suspension is Volvo’s dedicated rear suspension system for construction applications. Used around the world, Cantwell says its articulation range (17 inches from corner to corner) provides excellent off-highway performance, and its four-wheel-locking ability allows it to power through extremely sloppy ground conditions. “And there are no serviceable parts on the T-Ride,” Cantwell adds, “so maintenance demands are not a concern.”

Cantwell likes the Allison automatic transmission for this truck. “Now that Allison has introduced new pricing programs for its vocational automatics,” he says, “it’s possible to spec one for your truck and pay only around $4,000 more than you would for a manual truck transmission. But owners generally recoup that initial investment in the first two years of truck ownership in reduced clutch repairs and driveline maintenance.” Another transmission option for more skilled gear-jammers is the Eaton-Fuller LL 10-speed gearbox. “It’s a good choice for this application because of its excellent low-end pulling capabilities,” Cantwell says. “And low-end torque is always welcome on a construction truck.”

5500i with “Centipede” axle concept is International’s answer
Mark Nienas, vocational product manager, International Truck & Engine, looks upon this as a niche application, simply because of all the conflicting demands placed on this truck. “For those reasons, I recommend the 5500i model with a set-forward axle and a Bridge Formula package,” he says.

Nienas says he’d spec the truck with 12-1/4-high tensile, 3/8-inch-thick frame to provide the backbone for a truck that delivers unusual light weight and the ability to transport up to 26 tons of payload with an 80,000 pound gross vehicle weight rating. “To do this, the chassis is fitted with three Watson Chalin ultra lightweight pusher axles with 17.5 tires and aluminum wheels,” Nienas adds. “The truck’s all-aluminum cab, fiberglass hood and steel, piano-hinged doors all help keep the weight down. And a ‘Strong Arm’ frame configuration allows for a 107-inch overhang that optimizes payload, giving this straight truck the hauling capacity of a tractor-trailer.”

According to Nienas, this so-called “centipede” configuration, based on the six rear axles (including a stinger) has several years of reliable service behind it. “It’s also called a ‘Super 18’ body,” Nienas notes, “and is a proven performer in Arizona. The oldest one in the state is now more than five years old and has more than 400,000 miles under its belt as a severe-service and aggregate heavy hauler.”

This particular 5500i has a 258-inch wheelbase with 50-degree wheel cut and steerable axles, which Nienas says allows it to work well in city traffic. The Strong Arm can be lifted easily and creep speed used for precise backing operations. “The body is a 17-foot, 6-inch steel dump body with 22 cubic yard capacity,” he adds. “This body is custom built in Arizona for International and is a great match for this application.”

Cat’s 430-horsepower C13 is Nienas’s engine of choice. He’d mate that engine to Eaton-Fuller’s RTO 16908LL manual transmission with a 4.10 gear ratio and Meritor RT46-160P drive axles. “That would require a Chalmers HS 46,000-pound rear suspension,” Nienas adds. “But all told, this powertrain combination would deliver startability of 33 percent at idle rpm. A 76-mph top speed can be obtained with 1 percent gradability at 60 mph under load at 80,000 pounds gross vehicle weight.”