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30th January 1923
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Which of the following most accurately describes the problem?

Will the Giant Single Tyre Gradually Displace the Twin Tyre ?

AMONGST ALL those things in connection with the heavy motor vehicle which have become, by long familiarity, almost, as it were, second nature, there is none which would seem to be less susceptible of alteration, more permanent, than the twin solid tyre equipment of the rear wheels. The engine might be a " twin," or a "four," it might be a " six," or even an " eight " : the tyres would still remain twins.

It is true that certain disturbing factors have made their appearance of late, as, for example, (1)

the occasional use of three tyres, of which one was credited with certain anti-skidding properties ; and (2) the tendency to look with favour on the giant pneumatic. So few have these defections from established custom been, however, that they might almost have been said to be as indicative of the proper procedure in tyre equipment as those few fine


days of 192'2 were of the real flavour of a. right good English summer, to which we are all properly inured. The few pneumatic tyres which were used last year did not spoil the market for solids, any more than the two (or wan it three?) fine days spoiled the summer. However' they may have had their significance: it looks very likely that they had. We may see the day when all our heavy vehicles are on pneumatics, and we may also, although it is less likely, have a fine summer—some time! The wise owner of a fleet will keep a sharp look out, for, although one swallow does not make a summer, he is generally the forerunner of many, which are not likely to make their appearance if there is no summer in the offing. Similarly; although the presence of a vehicle or two on pneumatics does not necessarilymean that all the other fellows are out of step—behind the times—it does mean that somebody is trying the matter out, and that there is, at: least, a prospect that he may discover something good. Now, all this is by way of leading up to a plain hint that those heavy commercial motors which may -.,. occasionally be seen traversing our beautiful roads on single wide solid band tyres are not doing it just so that they may be different..from everyone else, or . nearly everyone else. There is method in their

madness, and it may be just as well for us to think the matter out now, so that we shall be the more ready to make up our own minds when the question " twins or large singles? " comes before us for decision.

The twin tyre resembles a certain well-known little coloured lady, by name Topsy, in that it was not I:orn, but just " growed." The early rubber-tyred commercial motors were not heavy, nor did they carry heavy loads. The tyres were, therefore, comparatively small ; toosmell, as a matter of fact. At any ratettheyewere gle. As time went on and larger and larger machines were fitted with rubber tyres, the 'need for larger tyres arose and rapidly passed beyond that stage when it could be met by single tyres. Not only were the dimensions of the single tyres which would be necessary for the loads such as to make them unwieldy, but it was impossible, with the knowledge then availa.ble, to turn out, as a single tyre having a wide tread, a satisfactory article. The fairly obvious course was, therefore, followed of fitting two smaller tyres in order to carry the load. It must be admitted, too, that the results of that, as it were, extemporized solution of a difficult problem, have been •quite passably successful.

Time and tide, however, do not wait: nothing in this world stands still, and success; whether small or great, but breeds the desire, even the necessity, for still more and further progress. Further success in connection with solid tyres for heavy vehicles must take the form of increased mileages—or so, at least, would the average user opine—and makers of tyres, for their part, believe that the substitution of the single broad tyre for twins will conduce to that end. Progress in that direction has taken the form of improving manufacturing processes to such an extent that it is now possible successfully to make tyres of this type up to twelve or even more inches wide. The tyre makers' opinion is being borne out onditions, , to keep efit of the of twins ved, and, the conmileages, ed. (4) An early single tyre.

in practice by tests under comparable and users would do well, as I have hinte their eyes open if they would have the be latest and best. Mileages exceeding thos by so much as 50, per cent, have been achi in certain circumstances, particularly whe ditions of use are unfavourable to high even better comparative results have accr The single tyre is stated to be betterl than the other for several reasons, but the most 'mportant one, that which counts, is that it dois not so frequently have to support occasional 1 cal over loading, as does one or other of twins. I does not require a tyre expert, or an expert of an kind, to realize, for example, that when a vehicle is travelling along a steeply cambered road, the lo d cannot possibly be evenly distributed over all fo r tyres of a pair of twins. The inner tyres are carr ing most of it, and, in exceptionally bad eases, th may be carrying practically all the load. Pot I oles are frequently encountered, too frequently, a a matter iof fact, and in the majority of instances, f only as the outcome of the driver's effort to av id them, they are crossed with one tyre on the ci ge of the hole and the other hanging over the dip. In such

circumstances, 'the whole of the load on the wheel is carried by one of the twin tyres. If, in conjunction with the consideration of these circumstances, it be borne in mind that rubber tyresaof all kinds are -particularly susceptible to damage as the result of even temporary overloads, and particularly so, again, if that loading is local, the line along which improvement must be effected beconzes apparent.

The single wide solid tyre, with flat tread, such as is illustrated by the accompanying sketches, does not suffer from any of the disabilities which I have just enumerated. It will conform to the surface of any cambered road which the ordinary user is likely to encounter. The inner edge of the tyre will, it is true, be compressed to a greater extent than the outer, thus proving that it is taking more than it fair share of the load, but even the outer edge will be taking a proportion and, even in the worst possible conditions, the whole section of the tyre is actually supporting the stress. On the other hand, in many cases, the outer tyre of twins may be free. and untouched, since there is no real connection between the two.

A similar comparison, again favourable to the single solid, may be made in connection with the striking of a pot-hole. The actual area of tyre in contact with the road may be no more in the case of the single than it is with the twin: the fact remains that the reaction, in the former, is taken across the whole width of the wheel tyre, instead of on half. The effect is materially to reduce the local overloading, and toincrease the tyre's chances of life.

That is the main reason for the superiority of the single solid. Other advantages are that there is no lodgment for stones and flints, such as is afforded by the space between the twins. Again, for practically the same price, the quantity of rubber available for wear is increased by an amount equal to that which fills Um space which would exist in the case of twins.

The problem of skidding, which may occur to the reader as being likely to arise in connection with the use of these tyres, is solved by cutting three or more grooves in the tyre, as indicated in our illustrations. As these grooves may, at a trifling cost, be recut, and the anti-skidding properties of the tyres restored when they are worn to such an extent as to make that operation seem desirable, it appears that, on balance, the advantage lies with the giants.

It is more than likely that the single tyre will rapidly find favour in the Dominions2 and in partially developed countries, where the particular advantages a the giant single (in that it shows a better return, in regard to the percentage of increased mileage) are likely to stand out. There is another reason, however. Most commercial vehicles in the Dominions and overseas are under-tyred, and, by their construction, cannot be equipped with tyres of a ,greater section than those for which the wheels and adjacent parts are designed, and with which they are fitted as exported. The giant single, with its greater area of section of rubber, and its better resistance to load, offers a solution of the difficulty which has already become apparent in many places abroad, and which will soon be appreciated almost universally. At any rate, the makers of this class of tyre are already feeling the effects of this circumstance, in the way of increasing export orders.


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