DRIVING FULL CIRCLE

DRIVING FULL CIRCLE

 Mercedes-Benz AMG GT R

Mercedes-Benz AMG GT R

They’re reinventing four wheel steering. It’s never really been away. A couple of dozen cars currently have it. Mercedes-Benz, one of its pioneers, is to replace the control arms of the AMG GT R’s rear axle with electro-mechanical actuators, which turn the rear wheels up to 1.5 degrees. Up to 100kph they point the opposite way to the fronts, above that they point the same way.

Freddie Dixon put four wheel steering on a racing car in 1935 and in 1938, when Hitler opened the Berlin Motor Show, Mercedes-Benz had it on the Gelandewagen. (Picture below by Stahlkocher) I reported in the Sunday Times Magazine of 8 December 1985 DRIVING COMES FULL CIRCLE. “Now that four-wheel drive is established, the next big development in car technol­ogy is likely to be four-wheel steering. At last month’s Tokyo Motor Show every major Japanese manufacturer had cars that steered through the back wheels as well as the fronts. Micro-electronics make them speed-sensitive, so the degree of rear-steer is less, say, for chang­ing lanes on a motorway than it is for moving the car sideways into a parking slot. Most of those shown at Tokyo were still at the concept stage, but Nissan has a rear-steer unit actu­ally in production and already offered as an option on Skylines for the Japanese home market. Nissan claims it im­proves the grip of the rear tyres by up to 70 per cent.”

It wasn’t long before Honda was making a Prelude that, “You could drive a long way without noticing the rear-wheel steer­ing. But you would be insen­sitive not to be aware of the taxi-like turning circle and the responsive roll-free cornering.” In The Sunday Times Motoring 6 September 1987 STEERING CLEAR OF THE COMPETITION “The world's first production ear in which all four wheels do the steering will be on view at the Frankfurt motor show which opens on Wednesday and will come onto the UK market next month at a cost of £14,100. Steering an extra set of wheels might sound like a complication we could do without — to be best left per­haps to dumper trucks and combine harvesters. That would be to deny the advan­tages of easier parking and significantly steadier behav­iour on the motorway. The mechanism that achieves it is more ingenious than com­plicated, and relatively in­expensive.

The £3000 difference be­tween the four-wheel steer (4WS) 2.0i-l6 Prelude and the similar EX version is mostly accounted for by the 16-valve (as opposed to 12-valve) en­gine and the more handsome specification. In West Ger­many it only costs an extra £640.

“Selling us something we did not even know we wanted is a singular skill of Japanese marketing. Yet there is a strong technical rationale for augmenting the front wheel steering.

Turning conventional steer­ing does not yank the front of the car immediately sideways. Instead the car yaws, that is to say it tends to lean over while turning, the back wheels following the change of direc­tion a moment later.

“It is this time lag that rear- wheel steering is designed to fill. If the steering wheel is turned more than a third or so, the back wheels deflect in the same direction as the front so the car moves almost bodily sideways. I tried it on a closed-off section of autobahn where a lane-change manoeuvre had been laid out. A con­ventional two-wheel steer car leans towards the outside of the swerve. A four-wheel steerer re­mains flat and level, enhan­cing control, feeling more precise and less fussy. It look a little getting used to. On the first few tries at 80kph I sent cones spinning. A few runs later, the skill was easily mas­tered at more than 100kph by leaving a little more clearance.

“Main road cornering has a similar safe feel. The rear wheels do not steer to the same degree as those at the front, a mere 1.5 degrees. It is sufficient for them to alter course only slightly to achieve the flatter, steadier movement that gives the Prelude a secure stance. The corollary of better cornering is improved manoeuvrability at parking speeds. Setting up the back car into a gap its own length has been an inventor's pipe dream for generations. Honda four-wheel steering is not quite like that.

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“After the first one-third of a turn of the steering wheel, the rear steering changes direc­tion. Instead of defecting the same way as the fronts, the back wheels counter-steer up to 5.3 degrees, sufficient to diminish the turning circle by a full metre to 9.6 metres. Four-wheel steering is the most radical development for cars since four-wheel drive. If there are disadvantages, they are not apparent so far. Only some 3,000 Preludes will be sold in Britain this year. It is an extremely well- proportioned two-door. 2+2 with a small back seat (despite more space this year), engineered to very high stan­dards. “

 

Motor Sport reported the Berlin Motor Show in March 1938. GERMANY’S CARS ON PARADE. Herr Hitler opens a show of technical novelties: “Another novelty on the Mercedes stand was the Gelandewagen, or "estate car." This would appeal greatly to British trials enthusiasts, as it has not only four-wheel-drive, but four-wheel-steering as well! Furthermore, the car can be driven either with front steering and rear drive, in the normal fashion, or with front steering and the drive on all four wheels, or with all four wheels both driving and steering. The changes in the various mechanisms may be effected easily from the driver's seat by means of two extra levers. The car, which has a 2-litre 4-cylinder engine, has a 5-speed gearbox, in which bottom gear is in the neighbourhood of 40 to 1. It has a maximum speed of about 53mph. The Gelandewagen, as its name implies, is designed for travelling about over very rough surfaces, as for agricultural or hunting purposes, or for military use. All four wheels are independently sprung, and, as a matter of fact, both front and rear axles are identical, except that one faces forward and the other backward. The steering linkages, the differentials, the means of taking the drive, and the suspension systems are the same in both cases. With the four wheel-steering in use, the Gelandewagen can turn round in a circle of only 7 metres.”

Frederick William Dixon (1892-1956) designed a racing motorcycle with a banking sidecar and was successful on two, three and four wheels, winning two BRDC Gold Stars. At the age of 40 he also invented an all-wheel control system. In1932 he led the Ulster TT for four hours before crashing his self-assembled Riley through a hedge. His engineering became the stuff of legend for racing driver APR Rolt, who encouraged work on four-wheel drive, forming a partnership to exploit it, which later became Harry Ferguson Research when the Belfast tractor millionaire took an interest. By 1945 Dixon’s logical mind had gone beyond merely four-wheel drive and he developed and built an astonishing car on which each wheel was independently sprung, driven, braked and steered.

The front and rear axles pivoted centrally with a pull-rod mechanisms drawing the inner wheels closer and pressing the outer ones apart to follow through a comer. It was ingenious but not, alas, a success. Lacking modern hydraulics the prototype, through its tendency to navigate sideways, quickly earned itself the nickname of The Crab and was soon abandoned.