THE TREND OF TYRE DEVELOPMENT.
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Solids' Supremacy Challenged. The Two Alternatives. Which Will Win Out ?
The Case for the Cushion.
EVERYTHLNG points to the fact that, in the near future, determined efforts will be made. to oust the solid tyre from popular favour on many types of commercial vehicles. The issue really depends more on the experiments which are being conchicted by various manufacturers and large
, vehicle users than upon the pi.opaganda of the interested tyre makers. Nevertheless, this cannot be entirely ignored, because, in many cases, it is so obviously based on facts and actual performance. Were all the roads of the country as smooth as many of the London streets, it is probable that the Bohd tyre might have held the field for very many years. But, in view of the fact that road uevelopmelt has lagged behind road transportation, and that, in many parts of the country, the road surfaces are admittedly, quite unsuitable for heavy motor traffic, and that, in consequence, the road transport, vehicle has to run under conditions with which it really never should be called upon to contend, greater tyre resiliency is an urgent necessity in many cases.
Then, quite apart from the mechanical rkspect, there is the question of the passenger edrying vehicle, and-, as this sea-son is amply demonstrating, an ever-increasing n-wnber of people are turning to road travel, where the facilities are offered to them, in preference to the train. So that the question of comfort is becoming just as important in commercial Vehicles employed on passenger work, as it has been for very many years in the case of Pleasure cars.
Pneumatic and Cushion.
As iecent articles in these pages have shown, the pneumatic tyre has already become very popular in America, and the thin end of the wedge is now being
driven in to the tyre trade, in this country. In previous articles, the many advantages .claimed for the pneumatic have been outlined, and, in so far as they are proved, will undoubtedly lead to the adoption of the pneumatic for a. great variety of purposes. But, it is hardly to be expected that this type of
• tyre wir . or -can, oust the solid from every application in which it is at present used. As we mentioned recently, it is quite unlikely, for instance, that the London buses will ever be run on this type of tyre. But, with activity in the pneumatic field, comes a revival of interest in the possibilities of . the cushion tyre. Recently, under the heading of "Greater Tyre Resilience," we went very fully into the merits ef the Killen designs. That versatile inventor, Mr. Killen, has given much thought to the solution of the tyre problem -by means of the'cushion principle, and, with such a tyre in existence, it is hardly likely that the commercial vehicle world will vote overwh61iningly in favour of pneumatics before the respective merits of the two types have been very thoroughly examined.
The progress of both is bound to be comparatively slow in any case for a time, owing to the wheel question. 'Unless satisfactory arid inexpensive wheel conversion can be carried out, it is probable that many vehicle users will hesitate at the expense of fitting special wheels. So that the tyre makers must, while popularizing their tyres amongst users, endeavour to per
manufacturers to build vehicles specially equipped to run on them. ` 028
In viewing the respective merits of, the pneumatic and cushion tyre, certain considerations a-rise. Inthe first place, it is results that are required. AUprogress tiaroughout the history of transportation has been in the direction of time saving and the provision of greater comfort, and it is solely a question of which type of tyre will fulfil the necessary conditions with a minimum of expense and with a maximum of freedom from trouble..
Though pneumatics undoubtedly possess many advantages, it must be admitted that there are certain considerations which weigh heavily against them. There is, for instance, the question of the spare tyre. However much confidence a heavy vehicle owner might have in pneumatics, he would .hardly risk the possibility of roadside delay by omitting to carry a spare tyre against possible contingencies. It might never be needed., in which case, apart from-the extra weight-uselessly carried, which is considerable, the tyre would deteriorate. This is, tif course, equally the case with smaller tyres on touring ears, but in that case the value and the • weight are so much less.
Twin Tyres Simplify the Question of "Spares."
On lorries fitted with giant tyres, moreover, a spare is necessary for both, rear and front wheels, -as the sizes are dissimiliar, and it is here that one advantage of twin rear pneumatics is evident. Although objections are raised to the system, on the grounds of the unequal load which may be thrown upon the tyres and the difficulty of maintaining equal inflation pressUres, there is a great advantage in having tyres which are interchangeable on all wheels, and •which, moreover, are smaller, lighter and less expensive than giant pneumatics. Moreover, another advantage is that, with twin tyres, the inflation pressures are considerably lower, and a mechanical pump is not such a vital neeeskity. So, in examining the relative merits of pneumatics and cushions, the twin pneumatic system must-not be overlooked, _EC.S. it does not possess seine of the disadtantages which will weigh against the big pneumatic in competition with the cushion.
The resilience of the cushion tyre is, perhaps, notso gre"at as the pneumatic, though it is very much
higher than that of the solid. But it scarce heavily in the matter of reliability, as there is no possibility of collapse, such as occurswhen a pneumatic sustains a puncture. In the ease of the Killen type of cushion, many other advantages are elairaed. There is, for instance, the feature of ground contact. Under heavy loads, the tread of the Killen tyre automatically distributes itself so that the area in contact is increased with the load. Moreover, it possesses the excellent feature that, when the load, is increased to a. maximum, the tyre has become better able to support it, and has, in fact, the supporting properties of the solid -with a, much greater area of ground contact. The pneumatic, on the other hand, under extreme conditioas of load, may possibly burst, but its strength would certainly not be increased.
Then there is the question of auxiliary appliances to consider.
Giant pneuanaties require a mechanically-driven pump. There is no question about that. We recently were present at an attempt to fill a giant pneumatic
by a foot-operated pump that was quite futile, taking.
time into consideration. So that the engine, or gear-shaft driven pump, is quite essential. Then there is the jack question. In order to raise the axles of a lorry sufficiently high to enable the larger sizes of pneumatics to be mounted or removed, jacks with a much greater lifting range than those in common use must be employed, The cushion tyre does not require such changes, and that is not the least of the arguments in it fav our.
In thus attempting to forecast what the trend of tyre development will be, one of the most important factors is unknown, and that is the rate at which road development will proceed undeir the new regime
of the Ministry of Transport. The necessity for resilient tyres being inversely. proportional to the degree of excellence attained in road eanstruction, the two are so interdependent that the influence of the road will have a great effect in deciding the ultimately most successful form of tyre.