Western Star Twin-Steer is Stable and Strong

Feb. 18, 2015

Here’s something you don’t see every day, unless you live in a place where the twin-steer 8x4 configuration (eight wheel positions, four of them powered) is used. That’s primarily the province of Ontario, Canada, where the axle arrangement is popular for dumpers and other construction trucks. But twin-steers, which offer stability and proper weight distribution, are also used under mobile cranes and concrete mixers and pumpers in the United States, according to Peter Schimunek, marketing manager at Western Star Trucks, which built our subject vehicle. He was my host on a frosty but sunny mid-January day at Eaton’s proving grounds near Marshall, Mich., where I did this Field Test.

This bright-white 4800SB (for setback front axle) dump truck was among a trio of Western Stars kept at the facility to show prospective customers and guys like me what the trucks can do in an on/off-road environment without using public roads, Schimunek said. The other trucks were a 4900 heavy-haul tractor and a 4700 10-wheel dump, longer and shorter versions, respectively, of the builder’s conventional-cab series. With him was Warren Rabb, an Eaton engineer and account manager who specializes in UltraShift Plus automated manual transmissions, with which all the vehicles were equipped.

Test Set

Truck: Western Star 4800SB Twin-Steer, conventional-cab vocational chassis, BBC 109 inches, w/ double-channel frame rails, GVWR 86,000 lb. (legal 79,200 lb.)

Engine: Detroit Diesel DD13, 12.8 liters (781 cu. in.), 470 hp @ 2,080 rpm, 1,650 lb.-ft. @ 1,650 rpm, w/ Jake Brake

Transmission: Eaton Fuller FO-16E309ALL-VMS UltraShift Plus automated 11-speed

Front axles: Meritor FL-941 40,000-lb. tandem w/ Sheppard M110 dual hydraulic power steering, on 40,000-lb. flat leafs

Rear axles: Meritor RT-46-160P 46,000-lb. tandem w/ driver-controlled locking differentials and 4.30 ratio, on 46,000-lb. Airliner air-ride

Wheelbase: 273 inches (front axle to center of rear tandem)

Tires & wheels: Front 425/65R22.5 Michelin XZY-3, rear 11R22.5 Michelin XDE M/S, on Accuride Accu-Armor polished aluminum discs

Brakes: Meritor S-cam drum w/ Wabco 6S6M ABS w/ Hill Start Aid

Fuel tank: 150-gallon polished aluminum

Hydraulic tank: 60-gallon polished aluminum

Body: Cobra 23-ft. polished aluminum w/ air-operated tailgate locks and flip-over mesh tarp

You might wonder if a twin-steer rig handles any differently than one with a single steer axle. Not much, I was surprised to learn after driving this one on the facility’s asphalt-paved test track and dirt trails. It reminded me of the various dump trucks I’d driven with single front axles rated at 18,000- to 20,000-pound capacity. They had 385- or 425-series tires on wide wheels, which prevented sharp cutting and therefore made for wide turning. To negotiate any right-angle corner, you start spinning the wheel early into a turn. So it was with this truck, which had 425/65R rubber up front. 

I asked Schimunek if the same weight distribution could be achieved more economically with one steer axle and a caster-steered lift axle placed where this truck’s second steer axle was (and I’ve seen some set up this way). No, he said, at least not off-road. There, lift axles usually need to be raised lest their wheels skew and tires plow into soft soil. Because a second steer axle is always on the ground, the truck is always firmly planted, and it will steer more positively, if not necessarily more sharply.

A turning circle is a function of wheelbase as well as wheel cut, so a twin-steer will turn as well or better than a comparable 6x4 with the same distance between the front axle and the center of the rear tandem. That’s also how the wheelbase of a twin-steer truck is measured, not from the center of its forward tandem, as I would’ve thought.

The spread between both sets of axles was 72 inches, a dimension that allows Ontario’s maximum legal weight on each axle: 9,000 kilograms or 19,800 pounds, meaning 39,600 pounds on each tandem and 79,200 pounds total, without using auxiliary lift axles. Steel flat leafs suspended the forward axles and an Airliner four-bag air-ride suspension from Freightliner, Western Star’s sister company, handled the rears. Even with a moderate load in the long dump bed, the ride was decidedly firm. As you’d expect, the truck also cornered without leaning, although I did use part of the test track’s super-elevated surface in the two sweeping turns, which I took at 50 to 58 mph. Without the banking, the turns’ speed limits might be closer to 35. I got above 60 mph in the straightaways.

Under the hood was a Detroit DD13 rated at 470 horsepower and 1,650 lb.-ft. It ran through a “9LL” gearbox, a vocational model that with a low-low section had 11 ratios in all. As an automated box, it shifted itself and automatically engaged and disengaged the clutch as needed, which was usually only during starts and stops; otherwise the box “float-shifted” as its electronic controls “talked” to those of the engine, which revved and backed off to facilitate gear synchronization.

The tranny started in the 2nd ratio unless an inclinometer sensed a steep upgrade, when it would select 1st. I could do that manually on the selector, and that could be better because while starting on steep hills, the truck would sometimes have to pause while the controls thought about the situation, chose a ratio, then restarted. Clutch engagement was always smooth, but shifting among low ratios at low speeds was often clunky, and the engine surged unless I braced my pedal-foot against the doghouse. At higher speeds, the engine and tranny smoothed out. There was no skip-shifting as there would be with more ratios or with an on-highway UltraShift, Schimunek said.

With transmission automation, the truck was easy to drive except when I got myself into trouble. This happened while attempting to climb a 20-percent grade that had been plowed after a snowfall a day or two earlier. Greg Andres, an Eaton systems engineer who was familiar with the proving ground, rode with me as I tried the off-road course and its hilly trails. Shallow hills were no problem, but the steepest one was slick with snow and ice, and I couldn’t crest the hill before the drive wheels spun. On the second try I slid down backwards because I had locked the brakes and the tires had no traction. Shame on me.

During these maneuvers Schimunek was running through the snow with his camera, recording my follies and triumphs. He had been riding with us on the wide bench seat to my right; it was adequate for two men but not near roomy enough for a cross-country trip, he and Andres agreed—not that such a journey was likely with this type of truck.

Western Star’s Constellation cab, adopted in the mid-1990s, is fairly wide with plenty of space for a burly driver and one other big guy. I remember when ’Star used the old Autocar cab that was narrow enough for the driver to reach over and roll the right-side window up and down, or maybe open and slam the door closed if it was rattling. Some drivers were irked when ’Star went to the wider cab, a rep told me at the time. This truck had power windows and the doors were tight. The photo of the cab’s interior shows its attractive trim, with faux wood applique across the dash and bright-metal bezels around the instruments: 15 (or was it 18?) condition gauges of various sorts and, of course, the centrally-mounted speedometer and tachometer, which were a bit small but still readable.

In Daimler Trucks’ galaxy of heavy-duty products for North America, Western Star is the premium brand, and every one of them—including the smaller dump and hefty tractor that I also drove—shows it in apparent top-notch build quality. Factoid: Although the chassis of all other Class 8 trucks I know of begin assembly upside down, then are turned over after axles, suspensions and other equipment are bolted on, Western Star frames begin their trip down the line right-side up. That’s how it was done in Kalowna, B.C., where the brand was born in 1967, and that’s how it’s done in Portland, Ore., where ’Stars are now built. The early engineers believed that it was less confusing for workers, and they would build a better truck. That commitment continues, whether there’s one or two steer axles.