A joy through the bends for more than 35 years

reading time approx. 3 minutes
Text: Oliver Schönfeld
Photos: BPW

The load-dependent self-steering axle from BPW makes it easier to manoeuvre HGV drawbar trailers and semitrailers and saves costs. Its patent application in 1986 was the starting signal for a real success story: it has become the standard for multi-axle trailers – thanks to an intelligent and simple idea.

If you can move an office chair or shopping trolley almost effortlessly in all directions, it’s thanks to its special castors: this principle is also found in steering axles with caster for HGV drawbar trailers. BPW supplements the self-steering axle with the innovative “load-dependent steering stabilisation”, also known as LL. It intelligently uses the weight of the vehicle to return to a straight line, which then ensures a high degree of directional stability. This enables BPW to provide optimal manoeuvrability; you can easily manoeuvre the trailer even in narrow spaces in delivery and distribution traffic, while the lower friction between the wheel and the road reduces fuel consumption as well as CO2 emissions. The tyres are protected and rubber abrasion is minimised. BPW was able to register the patent for the design in 1986, laying the foundation for a real success story.

Steering axles existed long before: BPW was already producing predecessor systems in the first half of the 20th century. In the 1950s, tractor steering axles represented a significant product area due to the advancing mechanisation of agriculture. But it was only with the load-dependent self-steering axle that the company invented a new basic principle that made the steering axle suitable for everyday trailer operation – combined with tangible economic and ecological advantages.

Trailer manages every bend

Swivel joints are arranged in front of the Rear self-steering axle on both sides in the direction of travel. Unlike conventional designs, this means that no complex cylinder reset is required. A new feature at BPW is the use of two undulating pressure wave discs, which provide the load-dependent reset. The axle beam and axle stub are connected to thrust bearings via steering pivots. When driving straight ahead, the wave contours lie on top of each other and keep the wheels on track. When the tractor unit is steered, the caster on the Trailer axle ensures that the wheels turn in. The contours of the waves shift and the discs push the vehicle axle and thus the entire vehicle slightly upwards. This allows the vehicle weight to be used by the mechanism.
When driving straight again, the vehicle weight pushes the pressure wave discs back to their original position. The track rod between the two wheel sides additionally optimises the steering geometry by keeping the wheels parallel to each other, thus keeping tyre wear to a minimum. When reversing, the movement of the track rod is blocked.
This video shows the “Economic miracle self-steering axle” – it dates from 2013, but is just as relevant today as it was back then.

Efficiency gains and ecological advantages

The fundamental advantages of a self-steering trailer axle speak for themselves, especially in delivery and distribution transport operations. Manoeuvrability in bends or roundabouts, when manoeuvring and turning is improved enormously compared to a rigid axle, and at the same time the load-dependent steering stabilisation leads to lower rolling resistance and reduced wear when driving forwards.

In addition to easier handling and better manoeuvrability, the efficiency gains are convincing. For a mileage of 100,000 kilometres, up to 1,000 litres of fuel and over four tyres per vehicle can be saved. And in addition to the economic benefits, there are also sustainable CO2 savings as an ecological gain. Extensive testing and many years of experience with thousands of self-steering axles produced confirm this time and again.

Even more than 35 years after the patent application on 21st May 1986, it is impossible to imagine trailer operation without load-dependent steering stabilisation. On the contrary: the joy through the bends has set a standard that brings many advantages for the user and for the environment.


For a long time, the self-steering axle only showed its advantages when driving forwards. The innovative Active Reverse Control auxiliary steering from BPW also provides steering functionality – and therefore trailer manoeuvrability – during reversing manoeuvres. The vehicle can therefore be manoeuvred quicker and automatically in reverse. Collisions can be avoided.

Which BPW patents from 125 years stand out in particular? Which products have had a lasting impact on vehicle technology? How did one innovation or another come about? In our new series, we present selected innovations “made in Wiehl” – and spectacular transports on BPW axles from past decades.
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