To Reduce Road Wear.*
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During the early stages, when smooth pneumatic tires only were used for the pleasure motorcars, automobilists were able to assert that the wear of the road was chiefly caused by horse-drawn traffic, and that their wheels only lifted and dispersed the dust which had been previously ground from the surface of the road by the action of the horses' iron-shod feet and by the iron tires of the wheels of horse-drawn traffic. This, however, cats no longer be said.
The problem of minimising the cost of road transport can no longer be confined to the vehicle, but the road surface and the vehicle that runs on that surface must he considered as a mechanical pair, just as in the case of the wheel and the rail on our railroads. I called attention to this nearly two years ago in a memoir I read before the English Institution of Civil Engineers in London on " Modern Motor Vehicles," in which I pointed out that the question of the improvement of the design of vehicles so as ter minimise road wear was of extreme importance, and I devoted n considerable portion of my paper to his part of the subject.
We must divide modern self-propelled vehicles into two classes: ist the high-speed pleasure vehicles which are almost invariably provided with pneumatic tires, and 2nd the heavier class of vehicles driven at a much lower speed and used for the commercial transport of passengers and goods on the roadways of Europe.
CN THE INFLUENCE OF CLIMATE ON ROAD SURFACES.
I do not propose to lengthen this paper by entering into the question of the substitution of tar binding for water binding of road surfaces, for it is now generally admitted that the substitution of an insoluble material of the nature of tar and tar products as a means of holding together the finer particles composing the surface of the road, in place of the water previously employed, can now be reckoned as a certain method of reducing the washing away of the finer particles in the form of mud during wet seasons, and the blowing away by the wind, or by the draught caused by the passing vehicles, of the fine particles in the form of dust during dry weather. We have therefore to suppose that this use of waterproof binding will be largely increased and that it will be a means of maintaining the surfaces of the roads of France and of Great Britain in a better condition than has been previously thought possible. But my purpose is to draw attention to one or two points connected with the vehicles themselves. Taking class I, the light, fast-driven motorcar, in what direction are we to look for improvement? Certainly we must protest as strongly as possible against any extension of the use of steel-studded tyres, in fact we ought to agitate for the suppression of their use and the substitution of other means of giving sufficient bite on the road surface to obtain satisfactory acceleration and to guard against the dangers of side-slip.
In the United Kingdom several promising inventions have
come to the front which seem likely to yield satisfs.wton
. results. They are all in the nature of presenting a rubber surface to the road, and that rubber surface of a much harder nature than has been hitherto used. With these hardened rubber surfaces it is possible to provide ridges or projections, or studs, all made of the hardened rubber, which seem to give the adhesion and security against side-slip which is required.
With the heavier class we meet with quite another problem. We have here to consider the transport of goods and passengers at slower speeds at the combined least cost of upkeep of the vehicles and of upkeep of the roads.
To my mind the most satisfactory solution of the future is the application of the driving power to more than one pair of driving wheels, in other words the distribution of the weight to be carried, whether this he passengers or goods, over several vehicles, coupling them together so as to get the advantages of only one driver and one conductor, and yet taking in one train of vehicles a sufficient weight of passengers or goods to reduce the cost for transport.
This is the problem which has been successfully dealt with by Colonel Renard and Mons. Surcouf in the Renard train, and it is to the introduction of the Renard train or of trains of the same character that we have to look for reducing costs of road maintenance. So long as heavy trains have to be hauled by one engine and the propelling force applied to one pair of driving wheels, as was the case with all earlier traction trains, both the vertical stresses due to the weight on the driving wheels, and the horizontal stresses applied by the driving wheels to the road surface to propel the train, must always he, so great as to make road maintenance costly, and it is probable that great economy will follow Colonel Renard's sub-division of these stresses. In addition to this we have to consider, both in the case of single commercial vehicles anti trains such as the Renard, the important question of the increase in diameter of the driving wheels used. Colonel Renard commenced with small wheels and in this he was probably wrong. In France, for commercial work generally, we everywhere find wheels of considerable diameter, and the credit for this wise choice of the French people must be given to General Morin's experimental researches made nearly too years ago. For heavy traffic traction engine designers have already endeavoured to minimise the wear of the road by using wheels of large diameter, those ol 2+ metres being very generally met with. Unfortunately in both England and France the designers of motor wagons that have recently come so largely into use, have lost sight of this and adopted wheels of only half, say 1 to t+ metre diameter, although the axle weights have been almost as great as in the case of the traction engines. No reasons have been given for this small wheel diameter except the convenience it affords of loading the wagons over the side, and of course the reduction in the tare weight of the wagons themselves, but I have already shcwn in a memoir read before the English Institution of Automobile Engineers that the increase of tare weight due to increase of wheel diameter is far less than has been commonly supposed.