Cab-under trucks – is an old idea returning?

Volvo’s autonomous electric prime mover, Vera, doesn’t have a driver, so the vehicle is little more than a chassis, wheels, electric motors, batteries and control units. It maximises freight space in a way that no driver-operated vehicle can.

However, this dream of maximising freight space in this way isn’t a new solution, back 50+ years ago, there was the ‘cab-under’ truck.

Tracing the origin of the cab-under truck isn’t easy, because several makers, on both sides of the Atlantic, have had a crack at it. It seems that the first commercial effort came from Bussing, in 1967, prior to that marque’s take-over by MAN in 1971.

However, even that effort may have been inspired by the US Air Force’s Minuteman Missile carrier, although that low-profile prime mover didn’t have a true cab-under shape. Later missile carriers have also adopted low-profile cabs.

The Bussing cab-under was a rigid eight wheeler: the Decklaster Supercargo 22-150. The model number indicated 22 tonnes GVM and 150hp. At least one of these trucks made it into the 21st century and was displayed at an historic truck show in Germany in 2011.

Bussing was the obvious maker to come up with this concept, because it was renowned for its under-floor, mid-engined truck range.

In Europe, the Bussing concept was picked up by Leyland, which employed a Leopard bus chassis as the base for a cab-under prime mover. The target market was car carriers and several were sold in ‘the colonies’. NZ’s Car Haulaways had the contract to deliver new British Leyland cars and John Baker bought one to haul Toyota cars in Australia.

John Baker had a significant influence on Australian car-carrying and was the first operator to cut the gooseneck off a wrecked car carrier and put in a drawbar, with a turntable behind the diff, under the chassis. That first tag-a-long trailer allowed him to extend the car frame over the cab and carry seven cars instead of six.

John could carry three Vanguards on the bottom deck and four Triumph Heralds on the top. His next step was hydraulic deck control, letting him stow four Falcons on the top deck – the first instance of angled vehicle cartage that has become common today.

But John Baker wasn’t finished innovating. His next prime mover was what he called a ‘UFO’ that stood for ‘Under Floor Operated’ or, as he said jokingly: ‘U Find Out’.

Like the NZ car carrier trucks, his UFO was a shortened Leyland Leopard bus chassis, with a fully-forward cabin, powered by a 671N Detroit Diesel two-stoke six, driving through an Allison automatic transmission.

The noise and heat inside that squeezy cabin must have been horrific, so John Baker well-earned his later induction into the Road Transport Hall of Fame.

The next cab-under initiative seems to be in the USA, where the Strick Corporation picked up the idea in 1977. Like the Bussing cab under, It may well have been inspired by the 1963 low-profile GMC-built Minuteman missile carrier prime mover, but made even lower-profile.

The Strick Cab-Under had four Rockwell axles and was powered by a Cummins VT-903, driving through a Fuller RT9513, 13-speed constant-mesh transmission. A few Stricks were sold, but the concept never proved popular – especially with drivers.

Probably the best known cab-under is the Steinwinter Supercargo 20.40 Cab concept that was unveiled at the 1983 Frankfurt Motor Show. Although only 1.2 metres tall, it had classy Euro styling, but importantly for length-restricted EEC TIR truck operators, the design allowed for an 18-metre-long loading area and a total cargo volume of 150 cubic metres.

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Manfred Steinwinter's truck was very modern for the 1980s, featuring independent air suspension, ABS brakes, a limited-slip differential and climate control. It was based on a Mercedes-Benz bus chassis and was powered by an OM442 400hp engine.

Steinwinter envisioned his concept as a modular one, because the prime mover could accommodate different engines and pull various trailer units. It could slide under a container skel, a car-carrier trailer, a volume van, or even a coach or bus trailer.

When bobtail, it could fit in with car traffic more easily than a normal prime mover.

I sat in the Steinwinter at the 1983 Frankfurt event and, although the seating was comfortable and the driving position very car-like, I was conscious of the fact that there was a lot of freight sitting just above my head and imagining rear-ending another heavy vehicle was disturbing.

Real-world evaluation began the following year and Mercedes-Benz immediately recorded engine cooling problems. There were also reported understeer handling issues. Mercedes-Benz declined any further involvement and although DAF and Isuzu initially were keen, they failed to pursue the project any further.

The test program of the prototype Steinwinter Supercargo 20.40 was terminated after only 3000 highway kilometres, but, before improvements could be made, the project was dealt a death blow. In the background, European road safety authorities didn’t like what they saw.

Not long after the concept was unveiled, it was announced that from 1990 onwards, the total length of a semi-trailer combination would be limited to 18.75 metres, of which the cargo area couldn't be longer than 15.65 metres. That meant 3.1 metres had to be devoted to cabin space in front of the trailer and swing-room clearance between truck and trailer.

The Steinwinter’s key advantage was lost.

However, given the old maxim that the more things change, the more they stay the same, the cab-under truck may return in a new guise, amid the electric revolution.