Twin-steer front axle trucks are rather common in Europe, as Johannes Dutch has shown us here on numerous occasions. After a discussion regarding their existence (or not) in the US, I looked up and found that Western Star, a division of Daimler, does make and sell one in the US. And not more than a couple of months later, I ran across this one parked by the Embers Supper Club, a popular C&W joint. So let’s take this behemoth in.
Generally, the axle loading restrictions have kept twin steer trucks from being practical solution in the US. Tag axles, which can be lowered under heavy loads and can typically steer passively, are more commonly found between the front and rear axles in those states where lower axle loading make them necessary for maximum overall loads. But these are two full-sized, full-time front axles, with interconnected steering gear.
Here’s the main (mechanical) steering gear, working on both axles.
Another shot of that. According to Western Star’s web site, these trucks have “dual main gears with dual ram assist”.
This is the other side, and that looks like the hydraulic ram for the front axle, in red.
And presumably the one for the rear front axle.
In back, the front two driven axles are on a Hendrickson Walking Beam bogie, a very rugged unit that relies on the the central pivot to allow the two axles to move up and down, but there’s no real springing per se, except for the rubber mounting blocks.
Here’s a better look at that. Very tough, but not nearly as soft riding as air suspension, which has become so common on big trucks.
But there’s the typical air suspension units under the last axle, which is not powered, and can possibly be raised. Maybe not on this unit, as it certainly wasn’t carrying a load.
A commercial plate, obviously.
I might have taken a closer look at the business end of this rig, to get an idea of how it attaches to the object it is intended to retrieve and tow. But I didn’t.
Under the hood is a modern four-stroke Detroit Diesel, which Daimler bought some years ago from Penske, who bought it from GM. There’s a variety of outputs, from the 400 to 600 hp available.
An impressive sight. And I hope to never have to need it.
I wouldn’t be surprised if the GVWR on this rig is high enough to make it unable to tow without creating a weight violation. Some of these very large wreckers are used exclusively for recovery, and smaller units are used for towing once these big units have righted a vehicle and put it on the road.
Good point. Wonder what this puppy weighs?
Im kinda baffed by the advantages of the twin front axles on this rig. European rigs definitely skew heavily towards COE setups which means the load is pretty evenly distributed up to the front axles. Even here, you see those passive steering deployable fromt/mid axles on dump trucks, cement mixers and enclosed truck and trailer car carriers…all of which would carry a significant portion of the load towards the front of the truck.
Here, the load would mostly be on the rear. I can’t imagine how the twinsteer setup helps, exactly. Does this somehow improve the turning radius?
Twin steer cabovers and conventionals use the same chassis, twin steer Western Star trucks and tractor units are common here as are every other American brand with that axle configuration.
All those axles of the featured truck and only two drives?
If I was waiting out in the mud for a 5-axle wrecker I’d hope something like this is what’s on the way:
Agreed! And actually just before seeing your post, the suicidal maniac in me caught the side profile of the featured truck and into my head pops the idea to lop off everything behind the cab, leaving a sawed off super-shortie rig. A screaming big block driving both axles (preferably still steering) would make a fun and insane wheelie/donut machine!
Quite a (long) beast. The biggest “local” tow truck I’ve heard of is this Ginaf M5350-TS 10×6. Axles 1,2,3 and 5 are steering axles. Axles 3,4 and 5 are drive axles.
You get twin-steer trucks in concrete pumper applications in the US relatively commonly. Also on stuff like crane carriers. Some of them will even be 8×6
Autocar:
https://www.autocartruck.com/construction-and-concrete/
Mack:
https://www.macktrucks.com/trucks/terrapro-series/
Wonder what they charge for a tow? Must be hugely expensive.
“I might have taken a closer look at the business end of this rig, to get an idea of how it attaches to the object it is intended to retrieve and tow. But I didn’t.”
The business end looks very typical for a heavy duty tow rig. There are two discrete components-
An axle lift is mounted at the back of the body (It mounts to the chassis and is folded straight up in the pictures). During use, it folds down and then extends under the front bumper of the towed vehicle to cradle the (solid) front axle. The lift then picks up the second vehicle using hydraulically rams. Operators use this lift for simple roadside breakdowns, since the rear tires of the towed vehicle remain on the ground.
Inside the truck body is a crane used for recovery work. It typically sits on a pivoting base, and this one has a three section extension. The crane would be used to lift a vehicle out of the ditch, turn a rolled vehicle upright, or lift a vehicle with severe accident damage onto a low boy trailer for transport. Since the invention of the axle lift, cranes no longer include a cradle (a cross bar a wide rubber straps used for towing).
This rig also has four corner jacks, used to stabilize the vehicle while the crane is in use. Think of the outriggers used by a backhoe- in the pictures they have yellow pads on the end, making them easy to spot.
I use to drive a gradall XL 4100 over the road. That walking beam suspension took an inch of my height. It is merciless!
Kenworth used to make a twin steer version of the K100 cabover which was even more European looking. These were mostly for the Australian market but some trucks were sold in the US, mostly specialty rigs for oil exploration that had heavy gear up near the cab, or wanted the second axle for lower ground pressure.
Eight wheeler Kenworths are quite common in New Zealand, the logging industry is rife with them.
Fantastic model, scale 1/25, I’d say. Very well executed, including the realistic layer of dirt all over the rig.
Using twin steer axles with flotation steer tires allows for better weight distribution over the length of the vehicle and keeps the truck within legal weight and length restrictions (sometimes called “bridge formulas”). Twin steer axles can also have the benefit of making a heavy non articulated truck more stable.
The axles used in the pictured tow truck are probably rated at around 20,000 lbs each and require multiple severe service power steering gearboxes. Peterbilt charged $20,000 for a twin steer setup when I worked with them in the eatly 2000’s.
Road, you mention working “with” Peterbilt … I worked for them for 5 years in the late ‘70’s to early ‘80’s. I vaguely remember some twin-steer COE’s at the time but no twin-steer conventionals. It seems that config is not uncommon for big tow trucks, and Kenworths and Petes can be thus configured by the factories.
That vintage Western Star were the last trucks to use the Autocar ‘Driver Cab’. Introduced in the late 40’s, the Autocar cab was adopted by White when they bought Autocar out in in mid-50’s. It was larger and more modern than the small White cabs that dated from the 30’s. In 1967 White introduced Western Star as a competitor to the large ‘West Coast’ conventionals from Peterbilt and Kenworth (you could throw the International Emeryville and Hayward built Western Macks in there too). Naturally the Star also used the Autocar cab, and continued to do so after the new generation White trucks debuted in 1977. Western Star was spun off a bankrupt White in 1980. The Autocar cab was finally retired in 2001.
Fort Macmurray,Alberta ,CANADA HOME TO THE WORLD’S LARGEST TOW TRUCK…….
The issue with any tow truck but especially the heavy end of the spectrum is maintaining weight on the front axles when loaded. The drive axles become the fulcrum of the lever, the heavier the towed rig the lighter the steering. Enter the heavy twin steer. More steering autority and more mass up front. The newer rotating wreckers can be spotted with their boom rotated 180 degrees above the cab when towing to try and get that weight transferred to the forward axles.
Lots of concrete trucks here in Vancouver, BC using those Western Star chassis…
Ocean Concrete even has their truck specs posted here: http://oceanconcrete.com/truck-specifications