1990 Honda Prelude four-wheel steering - GIF

[f800]

On the M1070 HET, the 4th axle steers. I understand that the 5 axles in the M1000 trailer steer to follow the tractor. I read that this was originally developed to maneuver through the European streets. The rear axle on my M1070 turns at a noticeably reduced angle from the front axle

[Frank S]

On the M1070 HET, the 4th axle steers. I understand that the 5 axles in the M1000 trailer steer to follow the tractor. I read that this was originally developed to maneuver through the European streets. The rear axle on my M1070 turns at a noticeably reduced angle from the front axle

The whole concept behind the 4th axle on the tractor and the 5 axles on the trailer are attributed to the Ackerman principle of steering geometry .
The inventor of the concept was a German Carriage maker Heir Georg Lankensperger patented by his agent in London Rudolph Ackermann The intention of Ackermann geometry is to avoid the need for tyres to slip sideways when following the path around a curve.[2] The geometrical solution to this is for all wheels to have their axles arranged as radii of circles with a common centre point. As the rear wheels are fixed, this centre point must be on a line extended from the rear axle. Intersecting the axes of the front wheels on this line as well requires that the inside front wheel be turned, when steering, through a greater angle than the outside wheel. [2]
Rather than the preceding "turntable" steering, where both front wheels turned around a common pivot, each wheel gained its own pivot, close to its own hub. While more complex, this arrangement enhances controllability by avoiding large inputs from road surface variations being applied to the end of a long lever arm, as well as greatly reducing the fore-and-aft travel of the steered wheels. A linkage between these hubs pivots the two wheels together, and by careful arrangement of the linkage dimensions the Ackermann geometry could be approximated. This was achieved by making the linkage not a simple parallelogram, but by making the length of the track rod (the moving link between the hubs) shorter than that of the axle, so that the steering arms of the hubs appeared to "toe out". As the steering moved, the wheels turned according to Ackermann, with the inner wheel turning further.[2] If the track rod is placed ahead of the axle, it should instead be longer in comparison, thus preserving this same "toe out".
Along with this the extended Ackerman principle in employed for the rear axle of the vehicle as well as the axles on the trailer relative to the distance behind the kingpin the axles will turn more or they will have a lessor turn angle At certain points throughout a maneuver an axle group may even turn slightly in the opposite direction briefly to insure proper tracking throughout the route of the turn radius.
If you have ever watched the baggage trams at an airport running around like large centipedes each trailer will track in the exact path of the tow unit how this is done is due to the length of the tow bar connection between them and the location of the hitch behind the rear axle of the preceding cart. The driver never has to look back to see if his carts will clear an obstacle because he drove around it so will they follow around it.
Trying to predict where the M1070 trailer will end up in a reversing situation takes a while to understand how the mechanics of the whole unit is designed