Shock-Shifter Hubs.
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Notes on Some Recent Experience with John Muir and Son's Speciality.
Quite a lot of people have heard about John Muir's " Shock-Shifter " hubs during the last year or so, but it is to be remarked that the number of individuals who are able clearly to explain the principle of their construction--to say nothing of their mode of action—is still strictly limited. "Oh, yes, I've heard about the 'shock-shifters,' but I'm not clear what it is that actually happens." This or some similarly-indecisive. coniment is the usual reply to a request for an opinion as to their feasibility. That definite and satisfactory results in running ser
vice have actually been obtained is readily conceded. The forceful personality of the inventor has unquestionably done much to make the " shock-shifter " known to many commercial-motor users, but, up to the present, road experience, and the data therefrom, have had to be acquired very largely at the expense of the proprietor of the patents. The user is a very-conservative person ; he is particularly loath, as a rule, to experiment with contrivances which he is not with facility able to understand. We are, however, informed that steps are now being taken to ensure that the shocks incidental to such one-man exploitation shall shortly be shifted, in part, to other shoulders.
For the past two years, from time to time, what have purported to be descriptions and criticisms of the " shock-shifter " device have appeared in print, yet a casual survey of several of these written opinions, we must confess, has instructed us but little. In order, therefore, to decide if we could usefully procure lirst-liand impressions, with a view to a short criticism and review of this device, that should finally assist many doubting users to form their oN,N n opinions, we recently sought from Mr. Muir an opportunity to test a set on the road and to examine such units as have considerable road-service to their credit.
We have prepared a special drawing, and have reproduced it herewith, in order the more easily to explain to our readers the principles which have been embodied by the inventor. The dominant idea of the whole device is to absorb the road shocks, and the effect, from the dynamic point of view, is much the same as many of those contrivances which are known as shock absorbers. We cannot subscribe to the suggestion, which has been made elsewhere on behalf of Muir's hub, that it enables the energy expended in overcoming obstacles to be turned into potential energy which can be applied to assist propulsion.
The hub is not, it will be seen, an integral part of the wheel itself. Interposed between the hub proper and the body of the wheel is an annular-shaped chamber, very-nearly full of steel balls. Lateral registration is secured by the provision of strong overlapping side flanges, whilst the permissible relative travel, in the vertical plane, of the wheel and its hub centre is limited by a number of equally-spaced check bolts which are located in the flanges of the hub, but which have ample clearance in the wheel proper.
We have described the " shock-shifter " chamber as being nearly-full of hard-steel balls, and it is upon the fact that the ball chamber is not quite full that the relative motion of the wheel and the hub depends. While running, the tendency of all these balls is naturally to cling to the outer wall of the annular chamber ; centrifugal force is, of course, responsible for that. When the overcoming of some obstacle on the road surface necessitates the bodily raising of the wheel, subject, of course, to the amount of deformation of the solid-rubber tire, the tendency is to displace the balls from their symmetrical position in the annular chamber and to cause them to become re-arranged in accordance with the relative motion of the wheel and the hub. While the wheel is moving, however, the balls, owing to centrifugal action, are constantly attempting to re-assume their symmetrical outer position. When they were displaced, they allowed the hub to become more or less eccentric with the wheel, but, when normal running equilibrium is again achieved, the balls compel the hub to return to its old position. It is presumable that, when standing, the tendency of the hub, owing to its weight, will be to push the lower balls out of the way (shown, exaggerated, in the diagram reproduced on this page), and to rest. eccentrically this, in turn, would, to sOTY1 extent, be resisted by the static friction of the balls. Once on the move again, however, the balls would force the hub to assume its practically-central position.
The device is almost the equivalent of a liquid bee.'. ing which cannot leak; the smaller the balls the nearer the approach to hydraulic conditions. The
reaction, which causes the recovery of the normal position of the wheel, and which plays the part, when the wheel is in motion, of the stored energy of a spring, is provided by the centrifugal action of the balls.
We reproduce photographs of steel and wooden driving wheels, which have undergone prolonged tests on motorbuses belonging to the L.G.O. Co. ; the Scotland Yard authorities would not permit these tests to continue, as they claimed that their weight did not coinply with the regulations. The chief engineer of the omnibus company, however, was satisfied with their running, and he is a critically-minded man. Their efficiency as road-shock-absorbing devices is unquestionable, and this has been definitely proved by the remarkable petrol saving effected in service by the L.G.O. machines. The effect of high road resistance is considerably reduced. From personal experience, we are able to testify to the shock-absorbing qualities of Muir's hubs ; a series of tests on a badly-sprung solid-tired touring car at varying speeds over one of the worst pieces of road in West London yielded remarkable results. If individual users can be convinced on such questions as prime cost, lateral stability after wear on the flanges, maintenance over prolonged road tests, weight and similar considerations, it is undoubted that Muir's hubs will effect savings in other running costs.