The Hydraulic Auxiliary Drive (HAD) starting-off aid offers additional traction when needed.

Down to earth: The Mercedes-Benz Arocs with HAD.

The Hydraulic Auxiliary Drive (HAD) starting-off aid offers additional traction when needed.

Photos: Matthias Aletsee


This is one of those mornings Bernd Schneider wants to be over with as quickly as possible. Like a grey veil the rain covers the gravel plant in Erkenbrechtsweiler on the Swabian Alb. It has been going on like this for hours with no end in sight.

And to make things worse, to make room for an oncoming dump truck, Bernd Schweizer in his Arocs 1848 has to pull over onto the muddy roadside while going up a hill.

Arocs with HAD in the gravel plant.
HAD: Maximum traction.

Full tractive force.

He anxiously looks at the rain-soaked track ahead of him while the huge tyres of the tipper as tall as a house roll by his window. Will the tyres be able to maintain traction on the muddy track? “Now the system can show what it is capable of”, says the 54-year-old. As he starts to accelerate, a blue symbol lights up on the display – the indicator for the Hydraulic Auxiliary Drive (HAD).

Additional power.

He activated the system upon entering the gravel plant with a switch on the dashboard. The high-pressure pump mounted to the engine now sends up to 450 bar of pressure to the wheel hub motors on the front axle. The pressure pushes hydraulic pistons outward, which in turn drive the cam ring. This creates an additional 40 kW of drive power at each wheel.

Simple operation. When needed, the HAD is activated via a switch.

Bernd Schweizer notices none of these things. The only thing he feels is that the front axle is now also involved in propelling the truck forward.

Bernd Schweizer and the new Arocs with HAD.

“It seems to have been made just for us”.

“The difference such a switch can make is truly impressive!”, says Bernd Schweizer. Joachim Schmid, his boss and managing director of Karl Fischer GmbH, can only agree. His company was the first to put the new system through its paces as part of customer field trials. HAD weighs 350 kilogrammes less than on-demand all-wheel drive and 500 kilogrammes less than permanent all-wheel drive. In addition, there is no rotating drive axle that increases fuel consumption. Fuel savings of up to eight percent over the all-wheel-drive variants are possible. Watch the video at RoadStars.

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