Tires for Vans.
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The Pneumatic the Ideal in Effect for All Vehicles Operating On All but the Best-surfaced Roads. Considerations of Commercial Expediency Tend to Limit Its Use to Light Vans.
The suitability of the pneumatic tire'for use on commercial vehicles is a constant theme of argument. A detail academic discussion of the relative merits of the solid and air-filled tire would fill many issues of this journal.
The actual difference in riding comfort as between solid anti pneumatic has been felt by most of us, also as between steel tires and others of more yielding material such as wood or rubber; this method of discrimination., through affording good first-hand notions of the relative shock-absorbing qualities of the various tires, is apt to give hazy notions of their valves.
A brief epitome of the general results of research and experience is, therefore, useful as directing ideas into the proper channel. In the beginning, a tire was a hoop or band, usually of iron, the use of which was to tie the fellies of a wheel in place. It was immediately recognized that in order that the wheel and its tire should be durable, it was necessary, in the construction of the latter, to provide against wear by making it somewhat thicker than was necessary merely for the original service of binding together the component parts of the wheel.
This tire is in general use to-day for horsed vans, its utility for any but those or the slow-running steam wagons is now finished. In the first place so soon as speeds ordinarily experienced in horse-drawn conveyances were exceeded, as in the bicycle and the early motorcar, so soon did the non-absorbant nature of the inner tire, in regard to shocks due to inequalities and small obstructions in the road, become apparent. In the horse-drawn carriage of the more luxurious type, the bodywork was suspended either from straps, themselves hung from the ends of elaborate springs, or from C springs, the effect being to provide a conveyance in which the passenger, at the speeds customary, was immune from vibration in any direction. It was the advent of the bicycle, a springless machine, that impelled progress in tire construction, which first showed itself in a change of the material for the portion of the wheel next the ground ; the tire proper, perforce had to be of some substantial and comparatively unyielding material, in order to fulfil its primary and essential function as a tie ; it became the practice to case it with some yielding material, the most suitable of which proved to be rubber. The epoch-making advent of the pneumatic tire of hollow rubber filled with air to afford additional cushioning occurred shortly afterwards. Similarly with the self-propelled road vehicle, this was in better case than the cycle, for it could be con veniently sprung. Structural difficulties, however, prevented the springing from being so complete as in the horsed-carriage ; the straps, or their equivalents, the C springs, which catered for shocks in a horizontal direction, could not be incorporated into a practical automobile chassis. It is this fundamental failing in the springing system of all motor vehicles—that it does not cater for the horizontal components of shocks— which calls for the fitting of a tire of resilient material.
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The other particular n which the iron tire failed when called upon for use on a self-propelled car was in respect of tractive efficiency, a property for -which there had previougly been no demand, at least as regards propb1sion along the public roads, In this also, curiously enough, rubber appeared to possess the necessary quality to a high degree.
In considering, therefore, the most suitable type of tire for any vehicle, the following are the points which should be reviewed : — . The condition of the road over which the vehicle is to journey, the speeds at which it will run, the weight and character of its load, and, finally, the question of comparative maintenance costs. As regards the first point. If a perfect read, without any obstruction of any kind, and level, could be found, suitable tires for vehicles to operate on it would be of perfectly rigid material, and the wheels would require to be exactly circular. On the other hand, the conditions set by a rough, cobbly road are best met by fitting large pneumatic tires of such a size that they need only be inflated to a low pressure. Now to deal with the second _point : speed. The • effect of sudden impact with ridges or obstructions in the road, such as those left by uneven repairing, or misplaced road material—it is these only in the main which impose horizontal shocks and which necessitate yielding tires—is not felt. at speeds of below eight miles an hour ; it does not become orreal consequence until 12 m.p.h, is exceeded. It would almost seem, therefore, that the legal distinction, be
tween heavy and light vehicles, which sets the limit at two tons unladen, allowing those under this weight to travel at speeds up to a maximum of 20 m.p.h,those weighing more must not exceed a speed of 12m.p.h.—would almost serve as a, line of demarcation for the use of pneumatics.
Our third consideration, of weight, is thus seen to be distinctly concerned with the second, as might have been expected, That the dividing line suggested in our last paragraph is not adopted_ in practice is because of the dominating effect of the fourth consideration, the cost of running. Considered from the _point of view of tire service only, irrespective of cost, the speed at which the vehicle is operated sets the style of tire most satis factorily. By this ruling all chassis of capacity up to 30 ewt. would be fitted with pneumatics, as well as a few two-tonners. On a cost basis, the conclusion's drawn are, unfortunately, different. In consequence, the limit of loading up to which pneumatics may be economically used is less than half the load given above, and, in but exceptional cases—we have in mind that of Selfridges, who use pneumatics on two tonners and all sizes below—the 15 cwt. van is the largest vehicle to which we should advise an owner to fit the more resilient tires. It is admitted, of course, that tha wear and tear of the chassis is less
with pneumatics, but, if this effect on a vehicle designed for pneumatics and shod with them, be com
pared with that on one designed for and fitted with solids, it will generally be found, and particularly in the larger sizes, that the saving in maintenance charges hardly justifies the additional first cost of the former tires if fitted to the latter type of vehicle without considering the higher upkeep figure which must be expected in the case of pneumatics. The consideration of converted touring-car chassis is beyond the scope of this article. Briefly, the conclusions which may be drawn are : For speeds of up to five miles per hour and with heavy loads, use iron tires, tbetween this and 12 m.p.h., solid rubber tires, above 12 m.p.h., pneu
matics. The last recommendation to be modified so as not to apply to vehicles for loads of over 15 cwt.,
except in special circumstances in which, absence of vibration is of more consequence than cost of running even here it might prove to be better, if loads are heavy, to use tires of solid rubber and to limit the speed to a maximum of 12 m.p.h.