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SPREAD THE LOA SAVE THE ROAD.

6th December 1921
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Page 12, 6th December 1921 — SPREAD THE LOA SAVE THE ROAD.
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Which of the following most accurately describes the problem?

The Advantages of "More than Four Whee Heavy Goods Wagon, the Public Service V( onfined to Any One• Type of Vehicle. The wry and Light Van can all be Improved.

THOSE who thoughtfully examined the situationin the early days of the war, when, for all practical purposes, progress in design was brought to a standstill, were impelled to wonder in whatiemanner the post-war motor vehicle, developed out of the most gruelling test to which motor mechanism had been, and apparently could be, subjected, would differ from its forerunners.

Radical changes in engine design seemed to be the basis of the most reasonable forecasts. Greatly improved methods of suspension were regarded as being extremely likely to be the outcome of the rough work in the war zones, but actually the most advanced thought was discovered in the practical application of a known method of increasing the area of .contact between the rolling medium of the vehicle and the ground. In this country. the chain track was developed to a high state of efficiency for a purpose of definite military importance ; the same motives operated differently in Germany, where designers aimed to dispose of the load over a greater number of wheels.

The chain track has great limitations when one comes to apply it to commercial uses, but the limitations attaching to a numerical increase of wheels are few indeed, and it is certain that, along this line, the development of the motor vehicle, whether it be intended for the carriage of goods or passen-gers, will proceed in the immediate future.

The Use of Six Wheels Already General. .

To-day, there is no qualified motor designer or engineer who is not convinced of the merit of the basic principle of carrying the load upon more than four wheels. No designer or manufacturer of a goods vehicle, intended to carry more than a ton weight or so, or of a motor coach, would dream of dispensing with twin tyres on the rear •wheels where solids are employed, 'whilst the twin pneumatic tyred wheel has, so far, been the admitted best equipment for the rear axle of the large private car or public service vehicle.

In effect, the use of twin tyres at the rear of a vehicle is the first stage?in the development which we are now foreshadowing. It is a means for spreading the load of the moving vehicle over a larger area of the road surface, with the primary object of reducing,tyre wear. With two surfaces abraiding and pounding one another, the saving of the one must involveethe conserving of the other, and, in this way, road surfaces already benefit by the increase in the number of points sustaining the load, made possible by the use of twin tyres. But this process must, and will, go farther.

There is, for instance, no justification for setting the limit to the number of wheels upon which a vehicle should be borne. Stability, when stationary, calls for three wheels ; stability at high speed calls for four ; practical immunity from risk, owing to tyre deflation, or a fractured or injured secondary steering connection, calls for six, eight, ten wheels—who can say to what extent the increase may, in reason, be taken'?

The disadvantages are few and may be taken first. An increase in the number of wheels and axles naturally entails higher manufacturing costs, some increase in weight, and also in transmission losses. This is the sum total of the price that has to be paid, and it is very small when set against it are the obvious advantages. Moreover, a big discount can be taken from these disadvantages, because the higher first cost will be returned over and over again in greater immunity from risk, lower running costs and lessened maintenance charges. The greater weight and larger transmission losses might entail a higher petrol consumption, but it is more than likely that, by careful design, the whole of this high fuel consumption will be recovered (or, in other words, avoided) by better adhesion, acceleration and retardation, in all of which there it ele

great scope in the motor vehicle for improvement. Thus, the disadvantages may be regarded purely as a means to an end, and' must not be considered by any means as a dead loss.

Let us now look at the advantages. Taking passenger vehicles first, merely increasing the number of wheels from four actually redunes the weight per inch of wheel surface in contact with the ground and brings the pneumatic tyre much farther into the realms of practical politics. So far, the giant pneumatic—" giant" in order to have sufficient strength to carry the load and to transmit the driving stresses—has obtruded too many of its disadvantages into the picture. The weight is great and a change of tyre on the road (by the driver and the conductor of the motor coach, for example) is a big task. The risks of a sudden deflation or of one less sudden are not measurable, and experience of such incidents has yet been in Pneumatics el Risk when a tj Greater comic Greater safety The factor oh Chassis parts < Fuel costs sho4 Road wear an Pneumatic tyrt Fragile goods t A heavier Iota, Unlimited sprt

sufficient to warrant there being given a definite opinion! under this head. The cost is great and the potential life problematical, but when we tome to consider the cm.ployment of the standard 120 mm tyre' we are on much suree ground. We know the capacity of this type of tyre, that it is easily handled and that its cost is low.

The use of more than two axles, therefore, would permit of the use of a greater number of small pneumatic tyres, offering many advantages besides low cost and ease of handling. • The risk of untoward happenings after the bursting of one of a number of tyres would be vastly diminished. The carrying of the load on more points of support would permit of the lightening of some parts of the chassis and body, thus serving insome degree to counterbalance the added weight and costs of the new parts. If the drive is distributed over more than four wheeis, there would be a distinct saving in fuel and tyre wear by reason of the virtual elimination of wheel spinning. With the normal type of two wheel drive, with a differential between the wheel shafts, the loss of contact between either of the wheels and the ground permits the engine at once to accelerate, the ." floating" wheel spins at an enhanced speed of rotation, and on striking the ground again undue tyre wear and road wear are caused. If, however, the wheels on the shaft of a second 'axle are in contact with the greund, one or both wheels of the front axle could be off the ground without the engine accelerating during the period of loss of contact, and the wheels thus rendered momentarily free from ground restraint would not spin and would return to contact rotating at the speed.at which they left it.

• To obtain wheel spin with a multi-driven axled vehicle, one wheel of each axle must be free of the ground, and the chances of this are, naturally, small—growing smaller as the number of axles increases. The greater part of all tyre wear occurs as the result of wheel bounding. Eliminate this and tyre costs will fall tremendously.

A material advantage is to be anticipated in the shape of a greater immunity from skidding on wet .surfaces when the number of separated points of contact i increased. The greater the number of them points of contact the greater the probability of a larg3 number holding the ground.

Greater Safety More Comfort.

There is, undoubtedly, a higher factor of safety in braking when the brake drum area is so much greater—as is possible when the number of wheels is increased. The risk of overheating the brake drums isPreduce,d. proportionately. The greater the number of wheels, the lighter may be the springs and axles, thus reducing that bugbear of all motor design—unsprung weight. The difference that all this would make to the comfort afforded by the 'vehicle to its passengers scarcely needs pointing out, for it ia. so obvious.

There 'no reason why the number of wheels that steer the vehicle should not also be increased. No difficulties are involved and there would be the practical advantage of a lessened risk from the failure of any detail of the steering gear. As a matter of fact remarkably few accidents of this kind occur, and when they do they are generally the result of the failure of a cross-rod joint or a steering arm, thus involving only one wheel. With, say, three other wheels under control, the vagrant wheel would easily be mastered. An increase in the number of axle's must make for safety in another direction which, up to now, has presented difficulties. The back axle, as being a point on a vehicle that remains nearly constantly at a definite distance from the ground, has been chosen as the component upon which to hinge the dig-in type of sprag. But there is some risk of a, sprag on the back axle,beirig iumped, and one or two attempts have been made to hinge the sprag on a frame member about amidships. This is not entirely satisfactory, because of the action of the springs. But with three or four axles there seems to be no justification for leaving off the wag from any vehicle That is likely to be called upon to travel in hilly country, and it would seem ae if a cumulative effect would be obtainable from a group of two or three sprags, one coming in after the other and thus serving to take up the shock gradually. When one comes to consider the goods vehicle, one finds that all of the advantages foreshadoweel for the passenger vehicle may be appropriated. We need only exchange " comfort " in the case of passengers with "immunity from vibration and breakage" in the case of fragile goods. Axle weights on the 6 ton (12 m.p.h.) and B ton (8 m.p.h.) classes would, by merely doubling the number of rear wheels, be reduced by about onehalf, but as these axle weights are permitted by law (with a revision of the law so much desired by men who have studied the questiont to allow of a greater total axle weight of vehicle proportionately to the number of axles), there is here a possibility, of a substantial reduction of the wage charge per ton mile.

Our illustrations show, in perhaps a rough-and-ready way, the legal types of vehicles now engaged in goods and passenger transport (except the small van, however). It would not he practicable to show the variations in each of the classes of goods vehicles permitted by law to travel on the road, these classes" being best defined by their permitted speeds of 4 m.p.h. (2 ni.p.h. in towns, villages, etc.) ; 5 m.p.h. ; 8 m.p.h. ; 12 m.p.h. and 20 m.p.h. In each case it must be apparent that great possibilities would be opened up by the employment of more than four wheels for the support of the vehicle and load.

It is almost impossible to go into all the technical details of a multi-ax led

vehicle. Thatsis a task which but very few designers have commenced to examine. Our description of the Ifustad sixwheeled chassis, in last week's issue, is probably the only published account of a vehicle which is borne on six wheels and is steered on four and driven on four. As a piece of design, the vehicle is extremely good, and we have hopes of being allowed shortly to examine the chassis itself and to make certain tests.

• One matter requires careful study, in view of the fact that, with the enterprise that characterizes the engineering department of the Lonaon bus service, it would surprise nobody to learn that an experimental multi-axled Three

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chassis was to be put into construction for London's public passenger services. The advantages of such a development would be very great, for it would

-then be possible to approximate more closely in carrying capacity with the 80-seated tramcar, whereas the largest existing bus—the S typo—now seats but 64. The probable need for providing two conductors, however, is, we understand, one of the objections to the further axles to a goods vehicle permit the use of pneumatic midway between them is tyres for the transport of fragile goods. on the circumference of the mean turning circle of the vehicle. If this axle be placed anywhere but at the rear, trouble occurs with the wheels to the rear of it. We do not regard with one atom ef approval the idea of making more than two wheels (the two referred to) non-steerable, for the wheels on the axle which is not in IIIVI.Til , line with the pivoting point of the

1 I vehicle must slip on the road sur ijj thus abrading the tyres and

I introduce strains on the bearings. If the drive be taken to an axle between the front and rear axles and the rear wheels be made to steer, the effect must be to swing the rear of the vehicle to right or to left on any turning movement, whilst it would be most inadvisable to approach nearer to a kerb or any other 1 obstruction than, say, six inches. All the wheels in front of those on the rear axle can be employed for steering purposes, and these all being forward of the non-steerable wheels would 'simply require to be turned in the same direction. With steerable rear wheels, set in a narrower track,

, the difficulties still present are the obtrusion of the wheel arches into the body space, and the sideways swing of the rear of the vehicle.

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Locations: London

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