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Bridge Work
Kenworth W900S 'Super 16' hauls asphalt.
By Tom Berg
Interstates are populated by five-axle semis until you venture into urban areas. There you see some strange-looking beasts that are legal under the weight laws of various states. While many eastern states still allow squat four-axle dump and cement mixer trucks, most western states have "bridge formula" laws that require long, multi-axle trucks.
That's why you see "super dumps" in places like Phoenix. Supers have six or seven axles under a 40-foot chassis — the maximum overall length allowed for a straight truck. Two or three liftable "pusher" axles are ahead of the tandem, but the truck's last 15 to 16 feet is all axle, called a "flying tag," "booster" or "stinger."
Under bridge formula calculations (the same ones that govern how heavy your semi can be), this long-slung axle lets the truck carry far more legal weight than it would if the tag axle were placed right behind the tandem.
Denis Strong, whose D&M Trucking in suburban Phoenix runs 10 Kenworth "Super 16" dumps, calls the flying tag "the single biggest thing to hit the dump trucking industry in the valley in the last 10 years." His 16-wheel dumpers haul almost as much payload, about 24 tons versus 25 to 26 for a transfer dump, the five-axle truck-and-trailer combination still common here. But the Super 16s are easier to maneuver on cramped job sites, and they dump loads in a few minutes instead of a half-hour.
Good equipment draws good drivers
So, how does a Super 16 drive? Strong sends me out on a regular run to find out. My host is Jerry Sparks, D&M's driver-trainer who looks and acts somewhat like a kindly professor. "I love this job," he tells me early and often during our 90 minutes together.
The chassis is a Kenworth W900S, "S" signifying the sloped hood from the T800 (see sidebar). Strong has run other makes but went to Kenworths partly to get its roomy, comfortable cab. Good drivers are hard to come by in this business, too, and like long-haul fleets, D&M has had to raise pay and add benefits to attract and retain good people.
Sparks is hauling asphalt to a paving job in southeastern Phoenix, and we are at a materials plant southwest of the city, waiting our turn to load. Over the CB, drivers communicate with each other and the plant's dispatcher to keep the flow of trucks smooth. Some are getting asphalt, like us, and others are picking up various grades of stone nearby.
Soon the dispatcher tells Sparks to back into the batch plant and he does. Coming in empty he had all the auxiliary axles raised, but now has to lower the Strong Arm somewhat to get its wheels under the plant's low bunker.
There is a slight thud as the asphalt stream first hits the bed, then we feel the suspension hunkering down as the payload quickly builds. Loading a single box, of course, goes quicker than the two boxes of a transfer dump. Sparks flips switches to lower the aux-axles as we move out from under the bunker.
Scaling shows we have taken on almost 48,500 pounds of product and the truck weighs right at 75,500 pounds. Sparks moves off the scale and begins heading for the road outside. "You want to drive now?" he asks. "Sure," I say, and we quickly switch seats. I adjust mine and buckle in, and we're off.
If you drive a "large car" tractor you'd feel pretty much at home in this dumper. The cab is the same as on any W9, T8 or T6, and the interior looks a lot like an over-the-road truck's. With no sleeper, the wall and rear window are just behind the seats. A look in the mirrors shows the rig is pretty short, especially compared to pulling a 48- or 53-foot trailer.
Way back there is that flying tag axle, whose tires I can just see in the mirrors. It stays in line with the frame, so there is nothing to worry about in a straightaway or shallow curves. But in corners it swings out, its wheels castering to follow the rear of the truck which pivots on the tandem. You need to keep that in mind.
'Strong Arm' tactics
From the plant we follow a rural road north toward the I-10 freeway. The road's blacktop surface is rumpled from age and the passing of many heavy trucks. We cross a set of railroad tracks and pause at a couple of stop signs, which gives me a chance to get accustomed to the workings of the truck's engine, transmission and clutch.
The Eaton Fuller "11-LL" is easy to shift, thanks to Kenworth's skill at setting up the lever and clutch linkage. You shift this tranny like a 9-speed on the road. A blue thumb switch gets you a set of five low-low ratios for starting out on steep grades or hard pulling off road. I don't need them on this easy run.
The Cat C-12 makes plenty of power and torque, and our acceleration is about what you'd do with a semi of the same weight. The ride is decidedly different than a semi's, though — slightly bouncy but not choppy, with a springy feel imparted by the Strong Arm. You know you're heavy, but in your pants you can sense the springs, air and mechanical, suspending it all on the road.
The pusher axles are on air bags and their wheels caster-steer their way through corners. They're wired into the backup light circuit and raise automatically when the transmission is shifted into Reverse. By law, adjustment valves are outside the cab to discourage cheating.
The Strong Arm is pushed down by hydraulic cylinders powered by the truck's power steering pump; the pump is oversized to pressurize the extra fluid. The axle is manually controlled and you don't raise it until you're close to the job site.
Tagging up
Our first turn is onto a freeway ramp. Sparks had told me the truck is top-heavy and that he takes corners slowly, so I do, too. "Take it real tight," he adds. "Stay close to the curb; that way the tag doesn't swing out so far and we won't hit cars that are going by us on the street." I do, and it doesn't.
The ramp leads down to the freeway and the Cat gets us quickly up to speed. I choose to cruise at about 60 mph, which is what most of the other truck traffic is doing. Again, I am conscious of our weight and the springy but firm ride, but having used the brakes and finding them quite strong, I feel OK about stopping.
The sloped hood and cutdown windows in the doors give good visibility to the front and sides, and the mirrors take care of the rear. Of course, one is never absolutely sure what's right alongside, but the peep hole in the passenger's door gives me some assurance before I change lanes.
We go about a dozen miles as Sparks directs me through downtown, off the 10 to the 202, past the airport and into Phoenix's east side. We exit onto a long ramp that glides down to a wide boulevard. The Jake and service brakes easily slow us to a stop. I turn right, again staying close to the curb, and continue to the next light. I make a hard right onto a narrower street. Our destination is just ahead.
"Get into the left-turn lane here," he says. I do and stop opposite the driveway to the job site. "We'll raise the axles before turning in. Get the tag up so we don't clip anybody going by." He points to a fat toggle on the control box on the floor between our seats. I try to flip it but it won't budge.
"You have to pull it up," he explains. This keeps you from hitting it unintentionally and raising or lowering the axle while under way. (If you drop it while empty, he says, it'll pick up the truck's rear, tandem and all, and you'll find yourself skating aimlessly around the road on the tag's free-steering wheels.) I pull and flip the toggle and can see the wheels begin to lift off the road.
Now the pusher axles. He points to the two switches on the dash, and I flip them. I hear hissing beneath and behind the cab as air is dumped from the bags over the axles and they begin rising. All the weight now is on the steer and drive axles, which are strong enough to take it at low speeds.
Pushing pavement
By now the tag is high enough to be out of the way, and I make a hard left and move to the job site. One D&M truck is just leaving and another is on the premises, and we wait a little before getting into position. Manuel, the foreman, and his men are laying down asphalt on a parking lot behind some currently closed retail properties.
Sparks has offered to coach me through dumping the load into the paver, something I'd never done. He climbs on the running board to my left. "Okay, back it right toward the machine." It's about 100 feet behind us and is an easy, straight-on approach. I center the truck on the paver's pan.
"Okay, just ease back, watch Manuel for directions…" In the mirror, Manuel waves me back, then gives me a "stop" with his palm as I bump the paver. I shift to neutral, release the clutch pedal, throw a switch to release the tailgate, push a lever to activate the PTO and then use a joystick to begin raising the bed. It goes smoothly.
Product begins pouring into the paver. Manuel waves "enough," and I back off with the joystick; the bed drops back down. "Now keep your foot on the brake slightly," Sparks says, "to keep us against the machine." It begins pushing the truck as it resumes spreading the 2.5-inch overlay onto old asphalt. Lightly riding the brakes keeps the truck against the paver as it moves forward.
Every couple of minutes the paver stops, Manuel waves for more and I move the joystick again, raising the box. I can see the hot stuff spill into the paver amid small clouds of oily steam. As the box lifts higher, I feel a thump as the hydraulic ram goes into its second stage. Soon we're done, and Manuel waves us away.
"You done good!" Sparks grins. I thank him for the coaching and pull ahead and to the left, where he goes to the rear of the still-raised bed and scrapes asphalt residue from its lip and latch areas.
Our trip back to the plant on the other side of Phoenix goes more quickly because the truck really scoots while empty. I skip low-range gears while accelerating and quickly get up to speed on the freeway. There is a little more bounce but the ride is still good, thanks partly to the nice characteristics of the Chalmers tandem suspension.
Sparks says he knows that Strong is ordering a trio of Super 18s. With three pushers and the flying tag, an "18" may legally gross 80,000 pounds on seven axles carrying 26 tons of payload. "I don't know about them," he says warily. "I'm used to this now, and think I'll stick with it."
Easy Going
Jerry Sparks lives in Peoria, Ariz., a suburb of Phoenix. He is a cheerful 50 and a long-time driver, but is relatively new to dump trucking. He wheeled oil field trucks in California before coming to Arizona and did other work before signing on with Denis Strong and D&M.
"I'm grateful to Denis for giving me the opportunity," he says. "I love this job. Every day is different. Some drivers stay away from hauling asphalt because it can be tricky, but I like it. I enjoy the challenge of working with people." He means paving crews, who differ in methods and temperament. "I try to get along with everybody, and usually do."
Two liftable, steerable pusher axles and a Strong Arm tag axle allow this Super-16 straight-frame dumper to carry almost as much as a transfer dump (and as much as your semi), but in a more compact package. Even heavier Super-18s, with three pushers, are on their way to D&M Trucking. Inset: dash includes switches for pusher axles; switch for the tag is between the seats.
Maximizing the 'Bridge'
Kenworth's W900S uses the sloped hood and nose from KW's T800 — thus the "S" in the name. The W9's frame is made for a forward-set steer axle, which is needed here to maximize the wheelbase in the allowable 40-foot overall length. The sloped hood makes for good visibility, especially on job sites.
An Arizona "Super 16" has 16 wheels on six axles with a total "outer bridge," or distance between the first and last axles, of 35 feet, 8-1/4 inches. By "rounding up" under the bridge formula, this makes it legally 36 feet long. The bridge law's Table B specifies that this truck may gross 75,500 pounds on six axles.
Without a "flying tag" axle, a truck of this wheelbase could legally gross only 62,200 pounds on five axles. The Strong Arm stretches the outer bridge by 13 feet, enough to add 13,300 legal pounds, 300 more than it actually carries. Up ahead, there are 18,000 pounds on the steer axle, 16,000 on the two pushers and 29,500 on the tandem.
The Federal Highway Administration just announced a study of "specialized" vehicles, including dumpers and mixers. Depending on its findings, this study could someday lead to the government to make eastern states drop their squat, heavy chassis and use trucks with more axles like the "supers" with flying tags appearing in the West and elsewhere.
All aux-axles are raised at job site. Strong Arm raises way up and its wheels "toggle" out of the way for dumping asphalt into paver .
SPECIFICATIONS
Tractor
Kenworth W900S,
conventional-cab
non-sleeper, 112-in. BBC
Engine
Caterpillar C-12,
380 hp @ 2,100 rpm,
1,450 lbs-ft. @ 1,200 rpm
Clutch
Eaton Fuller 15.5-in.
7-spring ceramic
Transmission
Eaton Fuller
RTO-14909MLL 11-speed w/ low-low ratio set
Front Axle
20,000-lb. Eaton EFA-20F4 on multi-leaf steel springs, w/ Sheppard dual hydraulic power
Tandem
46,000-lb. Eaton DS462P on Chalmers 854-46-H-HS walking beam/torque rod suspension
Pusher Axle
12,000-lb. Hendrickson Ultralift on air bags
Tag Axle
16,000-lb. Strong Arm, hydraulically suspended
Wheelbase
252 inches
Brakes
Eaton S-cam w/ lightweight Centrifuse drums
Tires & Wheels
Bridgestone M844F 425/65R22.5 front, M711
11R22.5 rear, on Alcoa aluminum discs
Fuel Capacity
90 gallons
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