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Six-Wheeled Vehicles.

21st December 1905
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Page 1, 21st December 1905 — Six-Wheeled Vehicles.
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Which of the following most accurately describes the problem?

The idea of employing six wheels to carry a self-propelled road vehicle is not new : several designs were prepared close upon one hundred years ago, but excessive internal frictional losses caused the failure of the machines ab initio. There appears to be an inclination, both at home and abroad, to revive the claims of the six-wheeled commercial motor for use on common roads, and this tendency is sufficiently marked to justify a brief examination of the merits and faults which are necessarily found in mechanical systems of this character. The six-wheeled type is not unique—there are at least three variations. Without paying regard to any of the freak class, we may quote the more usual modifications of which examples are now on the market : these are (a) tractor fore-part, having front steering, with a twowheeled trailer attached through a swivelling table; (b) self-contained vehicle, with three axles, of which the centre one carries the driving wheels, and the extreme pair performs the compensated steering functions; and (c) selfcontained vehicle, with back driving axle, and a bogie forecarriage arranged to steer reciprocally in respect of its four wheels. The first of these is unmanageable in manceuvring and backing, as was amply demonstrated at the first Liverpool trials in the year 1898; the second scheme of arrangement is most readily handled, and allows the best load distribution, but is not free from the common disadvantage of all rear-axle steering gears, which is that one back wheel will mount any adjoining kerb in the process of drawing away; and the last-named, of which the Janvier lorry at the Paris Salon is the latest specimen, whilst it gives an effective three-point support to the frame, introduces both the steering difficulty immediately quoted and a material addition to the cost of construction.

Purchasers of commercial motors place simplicity and efficiency, coupled with reasonable prices, before a consideration of the degree of mechanical cleverness displayed in any system. They are concerned, primarily if not exclusively, with the results that will be vielded in regular daily service, and no amount of protestation will cause them to deviate from that cold, practical examination of the machine as a

whole which must so often make the inventor's blood run cold. It is effective performance of the finished unit that tells in the long run with the business man, who is not always conscious that the result is due to perfection of detail. Yet a detail which may command the highest admiration as such can be rendered useless if wrongly employed, and we feel sure that patentees would do well to keep the toot ensemble before them. This leads us to question whether the advantages claimed for the six-wheeled vehicle can be held to be demonstrated. Its advocates point to the introduction of lighter axle-weights, greater security against side-slip, and increased adhesion for propulsive effort : they maintain a discreet silence as to how it manceuvres in traffic. We must take these claims in rotation, for a vehicle which combines all the good features has yet to be .exhibited, though there is no reason to doubt the likelihood of our having one brought before us very soon : first cost and range of application will then govern its scope. Axleweights which are within the maxima allowed by the Heavy Motorcar Order, 1904, render four-wheeled vehicles, whether for goods or passenger traffic, sufficient for all ordinary purposes, and it is only the exceptional cases of very weak roads that will be better met by the introduction of two more weight-hearingwheels : as in railway practice, the axle-weight is an index to the track—given strong roads, fewer axles are wanted for equal loads. Whether side-slip would disappear with the adoption of a six-wheel drive is distinctly problematical. it will certainly be made no better by the tractor, bogie, or other articulated constructions, but the improved balance of a self-contained vehicle with a central axle should help : it has to be noted, on the other hand, that this arrangement will probably add greatly to the weight on the middle axle. Improved adhesion may be obtained by this greater central load, or by driving on all six wheels with, if one engine is employed, five differentials. Against these alleged benefits, however, there is the difficulty of the path taken by the wheels on the following axle, which, as has been indicated above, set themselves, when the front wheels are turned so much either way from a parallel to the longitudinal normal of the vehicle, as many degrees in the opposite direction, thus swinging the tail momentarily where it is not wanted. This flaw in all the systems advanced to date is sufficient to condemn them for use in Great Britain generally, whatever their applications may be in purely country districts.

We look with more hope for a development of the fourwheel drive. Until that method of propulsion is taken up with real thoroughness and seriousness, users will continue to be troubled with inadequate adhesion. The four-wheel drive has proved a matter of ready accomplishment where electric distribution is employed, but there are no great mechanical difficulties in the way of its successful introduction in conjunction with internal combustion or steam engines. We do not infer the placing of more weight upon the front or steering axle, because that imposes fresh difficulties : it is to have available fifty per cent. more road adhesion, and to secure the valuable front-axle " pull " to supplement the back-axle " push," that we believe the fourwheel drive will merit a relatively wide adoption, in the near future, for commercial purposes.

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Locations: Liverpool

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