Concerning Wheels and Tires Generally.
Page 74
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The Use of Solid Rubber Tires for Heavy Loads. Costs of Operation.
In the general introduction to this section, which appears overleaf, we have suggested the tire as probably the most important factor in the economic co-operation of the self-proyelled vehicle and of the propisrly-built highway. I °flowing this expression of opinion, we may now usefully set down some of the more important considerations which must be borne in mind by those whose business it. is to see that they get the best results in respect of wheels and tires. The solid-rubber tire is becoming more generally used for heavy loads on all kinds of roads every day. The limitations of the steel tire in regard to its transmission of road shocks, and to its inability to keep direction under certain road-surface conditions, have led users carefully to examine the economic possibilities of the employment of rubber tires. Resultant increased speed, which is a legal as well as nowadays an economic possibility, in addition to the consequent prolongation of the life of mechanical details, are practical results which it is quite possible to balance against the additional cost of the elastic tread.
In by far the majority of those chassis models which are now being found suitable for employment in all Overseas conditions, little attempt will, we feel sure, be made to be satisfied with steel-tired wheels. There are, of course, notable exceptions, but these are for such specialized machines as agrimotors, road trains, steam motor tractors and traction engines and the like. Where, of course, road conditions are of so crude a nature as unavoidably to result in too rapid deterioration of the rubber tread, there, of course, also, the steel tire will still be predominant. In the home country the rubber tire has enabled users of heavy industrial vehicles to obviate that entire dislocation of traffic which has hitherto ensued after the occasional heavy snowfalls to which the northern parts of the British Isles, at any rate, are not infrequently subject. Wooden treads have been tried in respect of such conditions, and it must be admitted that, for certain classes of work, if the wooden blacks be securely held, be easily removable, and be formed of wood with its grain on end, such special method gives quite satisfactory results. Combinations, too, of rubber and metal strips have been used, but our experience to date is not entirely satisfactory in regard to such specialities.
For operation on first-class roads, such as those which are found in and around many great cities of the world, and occasionally on the trunk roads in the more advanced countries, the pneumatic tire of ample section can be employed satisfactorily on light-van models, and, of course, on taxicabs. Under normal conditions, any well-known make of pneumatic should not cost more than 1.25d. per car-mile, as things stand to-day. In Fra.nce, particularly, constructors are inclined to employ twin pneumatic tires on the hind wheels of machines carrying a gross load a not. more than 25 cwt. English constructors, however, are by no means persuaded that this practice is a, good one. There are inherent disadvantages in connection with it, notably in respect of rapid dismounting and inability to secure balance of pressure between contiguous inflated tubes.
It is, rather, in regard to the solid-rubber tire of which most must be said, for it is upon the success attending the use of this type of tread that the indnstry depends so much. On the nages which follow will he found a number of ca.refully-comniled notices concerning, amongst other specialitieq, the solid-tire products of the best-known manufacturers of the world.
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We make no attempt here to draw comparisons between the manufactures of this kind which are produced by the best makers. As a matter of fa,ct, there is little to choose between at least a dozen ot the bept brands. We refer readers in this respect to the amply-worded business announcements in regard to solid tires of all kinds which appear elsewhere in this issue. The manufacturers themselves, who all, without exception, produce carefully-compiled catalogues containing a great deal of interesting information in regard to solid tires generally, will be happy to forward such literature to all genuine inquirers, and we have been asked in many cases to state that they will be particularly glad to receive carefully-compiled particulars with regard. to the nature of the surfaces of the roads upon which tires are to run, so that the most suitable types of treads may be suggested.
During the past, year, the best makes continued to compile very high average mileages, showing consequent reduction of running charges. Taking everything into consideration, including the present suppl.y of raw rubber, and the keen competition between the best makers, we may set down the average running costs of rubber tires for the principal classes of machines as follows: 2.5d. per car-mile for a 5-ton petrol wagon. 1.5d. per car-mile for a 3-ton petrol wagon. 1.75d. per car-mile for a 3-ton steamer. 1.00d. per car-mile for a. 30-cwt. wagon. 0.75d. per car-mile for a 1-ton or 15-cwt. wagon. These costs are based on the assumption that the tires in question will be used for roads of average good conelition.. It is impossible to estimate exactly for cases in which the road conditions are exceptionally bad, and our readers, with their own intimate knowledge of local qualifications, will more readily than we can, make allowances in this respect ; in some cases, of course, costs in respect of tires may easily be double those which appear in the above list.
One of the principal problems in connection with the use of solid indiarubber tires for Overseas purposes is the necessity of some simple means for mounting and dismounting them. It is only in special eases where it is economical to install a hydraulic press. We are pleased to note that the principal tire manufacturers are becoming increasingly cognizant of this important objection, and in the following pages we have occasion to mention smite a number of special methods which are already finding favour in this connection. A brief note with regard to wheels may be added. The wooden wheel, even for home use, is being used less and less for heavier models. The cast-steel wheel with Y snokes is being found to give excellent results for all classes of service. For Overseas use it undoubtedly has exceptionally-favourable qualities. The spring wheel, with a, few exceptions, has failed to secure general approval. A few of the most practicable schemes are now described.