The Section of the Solid.
Page 10
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The Difference Betvveen Paeumatic and Solid-tire Problems. The Need for Ample Sections.
British Value for Money.
In recent issues we have written of the position of the-solid-tire industry in this country at some length. We have of course arrived at that stage when foreign competition has, course, all practical purposes, disappeared, at any rate for the time being. The reasons why users should and now must show a preference for British-made solid tires are, in the main, obvious. But, apart from the sentimental aspect of the situation, the fact cannot be too well realized that, from the point of view of value for money, there is no reason now, nor need there be in the future, why British and other users of solid tires should employ any others than those made in British factories.
Costly Competition's Good Results.
During the past few years, the pace has been forced by very strenuous competition. It cost the participants a lot of money, but the net result, from the user's point of view, has been that the average quality is now very much higher than it was when first competition began to become so keen. It rests with the British manufacturer to see that the improvement which he has effected in respect of the quality of his products shall be reflected in the keenness of his appreciation of the commercial sides of the industry.
Impression that the Solid Calls for Little Care.
A lot of misunderstanding has existed in the past amongst users, which has undoubtedly arisen from a Jack of knowledge, not only of the intrinsic characteristics of a solid tire as a commercial-vehicle component, but also from ignorance as to the care that is necessary in regard to its systematic and satisfactory employment. There is a not uncommon impression that, whereas a pneumatic tire is relatively a delicate form of construction, dependent on comparatively thin rubber and canvas fabrics, and upon pneumatic inflation, subject, moreover, to frequent disablement if great Care be-not expended in regard to its use, the solid-rubber tire, being of a more robust type of construction, calls for little care during use. Indeed,, it is astonishing, when one comes to consider this aspect of the situation, to find how heedless the average user is of such factors as ample tire section, exact tracking of the wheels, the periodic inspection and repair of the tread portion of the rubber, and the necessity of replacement when wear has brought the available elastic depth to within 1 in, of the steel band.
The Compromise of Steel with Rubber, The problems which are peculiar to the pneumatic and the solid-rubber tires, respectively, are distinct. The pneumatic tire absorbs most of the obstacles with which it comes in contact. Its industrial relative overcomes such objects by riding over them and by deformation of the rubber itself. The solid-rubber tire is, as a tread, a compromise in respect of elasticity. The rubber, from the soft outer tread down to the nearly vulcanite base, is more or less resilient, whereas the harder lower sections are mechanically and directly bonded to the inelastic steel band which is its base. This has been found to be the only practical method of mounting solid-rubber treads of road wheels for modern conditions : the single exception to this practice remains on trial. The Clincher type of tire for heavy purposes has almost entirely disappeared. The result is that a modern commercial vehicle of any load capacity depends for the elasticity of its road treads upon the net resilient effect which can be procured from this combination of the elastic rubber band and the inelastic steel base.
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The Evils of Under-tiring.
These are hard conditions, and it is imprudent to expect that the rubber tire will yield its best results if care be not taken that the conditions of operation are made as easy as is practically possible. Take, for instance, the question of an ample cross-section. How many instances are there which we can all recall in which failure even to reach the customary .10,000 miles guarantee can readily be traced upon inquiry to the fact that the section employed is not one which the makers will recommend for the ultimate wheel loads which the user sees fit to impose. An under-sectioned tire will perish if for no other reason than from fatigue of the rubber. Rubber will not continuously withstand overload any more than will any other material Wanted--Maadmum Mileage and Resilience Together.
The user, we must admit, is not always inclined to look with a single eye upon the maker's urging request that be will adopt a heavier and, perforce, a more expensive section : we have often endorsed that advice in our pages. He is not disinclined very often to think that he knows better what the tire can stand than does the maker, and he perchance suspects that the latter is recommending the more expensive grade solely for the benefit of his own turnover. The customary 10,000-mile guarantee, as to the expediency of which there is nowadays considerable divergence of opinion, is also a stumbling-block in this par ticular respect. A rubber tire of heavy specific gravity will, perhaps, yield an exceptional mileage, and even a satisfactory one when overloaded, but the drawback to its use is, of course, its lack of resilience. A heavy, dense tire, moreover, is not so yielding when it meets obstacles, and it is, therefose, more liable to damage. The user has to bear in mind that the successful choice is the tire which will yield the maximum of mileage with the maximum of resilience. If the two combined have proved to be satisfactory, the choice of section cannot have been far wrong. The additional cost of a big section is always recovered by the aslievement of additional mileage. One well-known make of tire which is now, temporarily, out of the running, and of which users have always spoken highly as to quality, was always consistently advertised by the use of the following phrase : " It's the extra mileage that counts," and there was a wealth of truth in that choice of words.
The Best Tire for the Load.
Most of the principal British tire companies now issue booklets, which contain carefully-listed particulars of the sections which they recommend for certain axle loads. In one case which is before us, three loads per tire are quoted for each section which are permissible, respectively, in cases of " best city roads only," " best macadamized main roads," "average provincial roads and hilly districts." In the case of a 120 mm. tire, for instance, these three figures stand at 30 cwt., 27 cwt., and 211; cwt.
Care When In Use.
We have now written at such length as space permits of the necessity for users carefully to consider the proper section of tire which they must choose from the point of view of their own running economy. 'We will devote another portion of this article in a future issue to consideration of the care that should be expended on the solid-rubber tire when in use, and to other factors which make for satisfactory service.