The Cycle Industry/Chapter 8
CHAPTER VIII
CHANGE SPEED GEARS
One of the devices on a bicycle which has done more to popularize cycle touring than any other, with the exception of the pneumatic tyre, is the change speed gear.
It was shown in Chapter I that the diameter of the velocipede or high bicycle driving wheel defined the method of calculating gear ratio, i.e. the ratio or number of turns of the pedal crank shaft and the rear wheel of a safety bicycle. If the road wheel is 28 ins. diameter, and the gearing multiplies the revolutions of the wheel by two, that is called a 56-in. gear because the wheel circumference travels a distance equal to one turn of a 56-in. diameter wheel; if the ratio was one to three, the gear would be called 84 ins., and so on.
A change speed gear is a device that allows the gear ratio to be altered to suit the conditions of the road or the riding conditions prevailing at the time. A low gear ratio, one to two, for example, means that the rider is enabled to climb hills better but not faster; the power of the rider does not vary but the power strokes in pedalling are divided into a greater number of efforts in a given time. The higher gears are useful for normal conditions or for riding with the wind blowing on the rider's back or down slopes when the gradient is not steep enough to let the machine run down quickly by its own weight. Under the latter conditions, viz., with the higher gears in use, the rider's feet revolve the crank axle slower, but the ratio of gearing being about one to two and a half turns of the road wheel on normal or middle, and three to three and a half turns of the road wheel on top gear, the machine moves faster with approximately the same exertion; or to explain it another way, the rider has no need with a high gear in use to exhaust himself with rapid pedalling as he would do if he wished to ride fast with a normal single gear.
Some racing cyclists disdain the change speed gear and prefer a single gear of medium ratio, but for tourists, and particularly for women and elderly men, the change speed gear is a boon.
_p73.jpg) Fig. 19 |
Ever since the days of the first safety bicycle the advantages of a change speed gear have been recognized, but it was not until about 1900 that a practical device was marketed. Previous designs were either too heavy and complicated or their poor construction caused so much friction when the train of gear wheels was in use that cyclists preferred a single gear.
I think it was at the Stanley Show of 1900 that Linley and Biggs exhibited a change speed gear that was made by running a specially shaped chain over chain wheels that were wide enough to allow a lateral movement of the chain to shift it from a small to a big sprocket on the rear hub. This provided a change of speed but it entailed a jockey pulley to take up the slack of the chain because there was no arrangement to lengthen the distance between the chain wheel centres when the chain encircled the smaller sprocket, i.e. when the high gear was in use. To show that Linley and Biggs were very practical cycle engineers, very much in advance of their time, a device resembling their original idea has been patented quite recently, but is too crude to have much chance of competing with the refined hub gears of to-day.
Following Linley and Biggs' patent, the next device to claim attention was a two-speed hub made by a Manchester firm and designed by a Mr. Ryley. There had been the G. and J. two-speed hub, the Planet two-speed hub, the Paradox two-speed crank axle gear, and one or two others.
The Hub Two-Speed Gear Co.'s two-speed hub may be said to be the father of all practical hub gears and was sold in considerable numbers. Detailed explanations of these gears would not be understood by non-technical readers, so it will suffice to say that by means of a train of pinions and a sliding member operated by a rod passing through the centre of the hub axle, the changes of gear ratio are made. The rider moves the rod in and out by pulling on it through the medium of a small lever on the top tube of the bicycle, and a wire which runs over a roller from the lever end along the top tube to the roller and down the side of the back stay. The movement can also be effected by Bowden flexible cable from the handle-bar, thus making it unnecessary to release the handle-bar for changing gear.
While the Hub Co.'s two-speed was being sold and gaining considerable popularity, other firms commenced experiments with hub gears. Notable among these were the Eadie Co., who took up Pagan's patent, the B.S.A. Co., and the Raleigh Cycle Co., who paid attention to a three-speed hub made under the joint patents of Sturmey and Archer. Ryley, of Manchester, moved to Birmingham and began the manufacture of a three-speed hub at the New Hudson Co.'s works under the name of the Armstrong.
The three-speed hub was now an established favourite, and so rapidly did it gain favour that it was included in the specification of nearly every high grade bicycle on the market.
Armstrong's and the Raleigh Co. (Sturmey-Archer) laid down an enormously expensive plant of machine tools to deal with the gears on a commercial basis, and were able to so reduce the cost of manufacture that they had the trade to themselves. The only other change speed gear that has been retained by a cycle manufacturer is the original bottom bracket two-speed gear made by John Marston, Ltd. (Sunbeam). This is an epicyclic or sun and planet gear on the crank axle and is operated by locking or unlocking a central pinion surrounding the shaft. It is fitted as a standard article by the makers of the Sunbeam bicycle and has the great advantage that it is enclosed in a metal oil bath case and when the gear is in use the pinions revolve at slower speed than a hub gear, and are being constantly lubricated with fresh oil picked up by the chain wheel.
The production of the three-speed hub gear is now confined almost entirely to Sturmey-Archer Gears, Ltd., Nottingham, and the B.S.A. Co., Birmingham, the Armstrong gear having been merged with the Sturmey-Archer gear just before the war.
One might almost say that the production of hub gears is a special trade, because the accuracy required for the making of the parts is certainly more refined than is the case in any cycle factory where ordinary cycle parts are machined. Only by working to the finest limits employed in any branch of mechanical engineering is it possible to produce an intricate piece of mechanism contained in the space of a large sized bicycle hub. The plant, installed originally by the Raleigh Cycle Co., cost thousands of pounds, and cyclists certainly owe this firm a debt of gratitude for making it possible to buy such a beautifully made gear at a moderate price.
Motor-cycle Gears. The history of the change speed gear applied to a motor cycle is akin to that of the bicycle. The early forms were very crude affairs in comparison with the modern counter-shaft gears as they are termed to differentiate them from their prototypes, which were fitted in the rear hub shell. The motor cyclist very early called for a change speed gear, because his engine refused to give off power unless it revolved at a high speed, and slow travelling on hills reduced that speed.
The first motor cycles were tricycles, and they had gears of the sliding or compound type, then came the Roc gear patented by the inventor of the Wall Auto Wheel. The latter was an epicyclic gear in the hub, the change of speed was effected by locking first one and then the other of two brake drums by means of band brakes.
The first commercially successful gear, in so much that it was marketed in quantities, was the Armstrong, fitted to the New Hudson and afterwards other motor cycles.
Sturmey-Archer Gears of Nottingham followed with a similar hub gear. Hub gears lost favour with motor cyclists on account of the weight of the gear being in the wrong place, and because so many hub gears intended for solo riding were used with side-cars and passengers, and proved unequal to the task of the double work. The modern motor cycle gear is now almost wholly of the countershaft type, and contained in a separate box or case like the change speed of most motor-cars. The Sturmey-Archer Co. and the B.S.A. Co. have specialized in these gears, but many other firms make their own.
Still another popular type of gear used by two firms in particular, Rudge-Whitworth, Ltd. and Zenith Motors, Ltd., is the expanding pulley type. In both instances a belt is used but in the Rudge-Whitworth case both front and rear pulleys expand and contract, and in the Zenith patent only the engine pulley expands and the slack of the belt is taken up by sliding the rear wheel from and to the engine as the call for a low or high-gear ratio is desired.
For a technical treatise on motor cycle gears, I would refer readers to handbooks published by the proprietors of The Modern Cycle, Iliffe & Sons, Ltd., 20 Tudor Street, London, E.C.4.