Wheel Treads to Suit Road Camber.
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Extracts, With a Few Notes Commenting Thereon, From a Paper Recently Presented by Mr. A. E. Collins, M.Inst.C.E., City Engineer of Norwich, to the Institute of Municipal and County Engineers.
The struggle for supremacy between road and wheel has been evident almost ever since there have been roads which could be called roads. Wheels, of course, are vastly older than roads, and this perhaps might be deemed to yield to them a prescriptive right to the last word in argument, as to which of these two should be adapted to suit the other: But no such onesided procedure would be effective in these days of rapid development.
Road v. Wheel. Wheel v. Road.
As years go by wheel will follow the road, and road will follow the wheel, alternately, just as, to quote a particularly topical analogy, gun has forced the development of armour, and then again, armour has added to the penetration and muzzle velocity of artillery.
Road Maker and Road User.
The struggle is a ding-dong one. We find the road surveyor harassed by "interminable foundation and crust problems" pressing for a solution of the roadcum-wheel difficulty by the drastic limitation of axle loads, the widening of treads, the further employment of elastic tires, etc., etc. Meanwhile, wheel users are inclined to think perhaps that more should be done to bring the roads into line with the wheels, to build up their foundations, which is better in accordance with the requirements of the heavily-loaded axles of fast-moving traffic to-day.
Flat Tires and Cambered Roads.
Not the least interesting of the many problems to which this inter-struggle has given rise, is the very strict limitation to the usefulness, for load-carrying purposes, of the wider steel tires.. It is obvious that tires set accurately in the horizontal plane can in no way accommodate themselves to a road surface which is cambered at all, other than by cutting down to a flat path, from their inner periphery outwards. This is a consideration of so obvious a nature, that naturally it has received very close attention in the search for possible solutions from motor-vehicle constructors throughout this and other countries.
The Rubber Tire Adapts Itself to Camber.
The rubber tire eliminates any consideration of this kind, and with considerable efficiency renders it pos sible for the tread to adapt itself to the cambered road. The increased use of elastic treads on wagons of the heavier load-carrying classifications, is further limiting the trouble as between wheel tire and cambered road.
The old problem which Mr. A. E. Collinshas rediscovered and endeavours to solve, therefore, only concerns the heaviest typesof steam wagons, steam tractors, and traction engines generally.We reproduce below certain extracts from Mr. Collins's paper, which he recently presented to a professional Institute. Additionally we include, as illustrations, two of the drawings which he subunits will make provision for the automatic adaptation of tire surface to roadcamber outlines.
Extracts from Mr. Collins's Paper.
" Notwithsta.nding contrary opinions freely expressed by irresponsible enthusiasts it is impracticable within a generation to raise the standard of road construction throughout the country to economically withstand the heavy weights and high speeds which builders and owners of motor wagons, traction engines, etc., adopt. If the attempt be made to construct roads to carry such mechanical traffic as many owners appear to wish, the problem seems an impossible one to solve, haying in view the total economy of roads and conveyance. "Roads would be given a better chance than now if it were imperative that wheel diameters and widths were strictly governed to agree with their loading and where wide wheels are necessary, that they be so constructed or mounted as to pass equally upon the road for the whole width of wheel.
The Wheel Trouble.
" Indiarubber tires, provided they are not too hard, practically effect this distribution on roads of average cross-section or camber. Wide iron or steel tires only do so on roads of the camber the tires are made to suit. There is no standard camber for roads, and if there were, ordinary wear and tear cause changes therefrom, so that the adoption of a standard camber would not remove the trouble. It is obvious that ordinarily mounted wide wheels, made to suit a fiat camber, will bear on their inner edges when running on a road of greater camber and vice versa resulting in intense loads on narrow widths and unnecessary injury to roads. The presence of diagonal or other bars or projections on tires emphasizes this injury. In the endeavour to arrive at an intensity of loading which the average roads of the country should be expected to carry the writer has watched the action of ordinarily heavily-loaded cart wheels, and has come to the conclusion that an ordinary cart wheel of 5 ft.. diameter with 2!, in. steel tires loaded to 42 cwt. on the axle or g cwt. per inch width of tire does net cause unreasonable wear or damage.
"In considering the question of the amount of wheel tread-in contact, the flattening of the tire is negligible ; from numerous observations the length of are of tire in contact with the macadam when in average statei.e., neither noticeably dry nor wet— may be considered as 1 in, and the pressure due to the load 8i cwt. per square. inch of surfaces in contact.. . •
" iron or steel tires should not be permitted where they exceed acertain width (the writer puts this at 9 ins.) unless the wheels are so arranged as to adapt themselves to the constant variations in cross-sections —i.e., camber of' reads. The writer, before advancing this proposal has considered how it can he complied with, and has designed various alternative methods therefor, three of which are illustrated in the. attached suggestive diagrams which are submitted for criticism.''
Neither a New Problem Nor a New Sr■lution.
It must certainly not be .concluded by the author of these schemes that he has discovered a new method of meeting an old difficulty. Both of his proposals have certainly been considered in principle by numerous constructors and designers. We cannot recall at the moment any single individual design which has, in practice, perpetuated e=ther one of these particulars. The outstanding difficultyof either of these lines of advancement is the obvious one of greatly increased weight, if anything like the strength of existing live or dead-axle types is to be preserved, to say nothing of increased width or, alternatively, decreased stability.
Where Not to Put Disc Couplings.
The very clumsy method illustrated in the smaller of our two drawings shows large leather disc couplings. We fear Mr. Collins cannot possibly have experimented practically with a final drive allocating the maximum torque to joints of this kind. There appears to be no special reason why the quite remarkable De Dion final drive, which stood up so well in early motorbus operation, should not be employed in the manner that is suggested in Mr. Collins's second scheme.
It is good to find that surveyors are interested in possible mechanical adaptation of this kind, but there are very considerable difficulties in respect to the practical development of either of the schemes, which Mr. Collins advances, which have been considered and in all cases abandoned, -principally-on account of the weight trouble which we have already mentioned.