Page:EB1911 - Volume 03.djvu/940

 The Sturmey-Archer three-speed hub (fig. 15) has gear-ratios 125 : 100 : 80. In the high gear position the epicyclic toothed wheels are to the extreme left position. The chain-wheel is mounted by a free-wheel on a drive-ring, with which the ends of the spindles of the planet wheels engage at high gear. The sun-wheel, not shown in the figure, is held stationary, and the annular wheel engages with a ring screwed to the hub-shell, by means of keys engaging in notches. The hub is thus driven at a higher speed than the chain-wheel. For normal gear, the striking gear draws the internal mechanism of the hub towards a central position, compressing a spring, disengaging the sun-wheel and locking the drive-ring hub and annular wheel together. At low gear, the internal mechanism is drawn to the right-hand side, where the planet carrier engages with the end plate of the hub by means of claw-clutches. The annular wheel is still engaged with the drive-ring, and the sun-wheel is again locked to the spindle. The hub is thus driven at a lower speed.

Tandem Bicycles.—The weight of a roadster tandem is about the same as, or a trifle less than, that of two single roadster bicycles, but the frictional resistance of the mechanism, the rolling resistance of the tires, and the air resistance at a given speed are much less than twice the values for a single bicycle. Consequently, much higher speeds are attained on the level, and free-wheeling down hill is much faster. On the other hand for riding up hill on a moderate gradient, the effort required is about the same as on a single, while on very steep gradients the tandem is at a slight disadvantage. For the full enjoyment of tandem riding, therefore, a two-speed gear is a necessity, while a three-speed gear is better. In the Raleigh tandem (fig. 16) the frame design is such that it can be ridden by two ladies, and the strength and rigidity is sufficient for two heavyweight riders. The steering and control of the brakes is done by the front rider. Connected steering is employed in some tandems, allowing the rear rider to steer if necessary. For two expert tandem riders, connected steering is slightly more pleasurable than fixed handle grips for the rear rider, but on the other hand, divided control may lead to disaster at a critical moment. Most passengers on a tandem with connected steering unconsciously give the steering a bias in one direction or the other, putting a nervous strain on the steersman which becomes almost intolerable towards the end of a long ride.

Motor Bicycles.—Fig. 17 shows a touring motor bicycle, fitted with luggage carrier and stand, the latter for supporting the bicycle while at rest. The average speed of a motor bicycle being much greater than that of a pedal bicycle the stresses on the frame due to moving over rough roads are greater. This necessitates greater strength and weight in all parts—frame, wheels and tires. To take this increased weight up steep gradients requires increased engine power. The weight of a touring motor bicycle may be from 150 to 200 ℔ The drive is usually by a V belt of leather, or of canvas and rubber, the angle of the V being 28°. The engine speed at maximum power is from 1500 to 2000 revolutions a minute, and the belt gears down in a ratio varying between 1⁄3 and 1⁄6 according to the cylinder capacity of the engine. The possibility of the belt slipping slightly is conducive to smoothness of drive; chain-driving, except in combination with a slipping clutch, is too harsh. The principal defect of the belt drive is that the belt stretches, and on coming to a steep hill may have to be tightened before the bicycle can be driven up. The control of the speed and power of the engine is effected by the throttle, extra air valve and spark advance, the levers for which are all placed within convenient reach of the driver. As the engine is almost invariably air-cooled, the skilful manipulation of these three levers is essential for satisfactory results. On a good level road when the engine may be working at a small fraction of its maximum power, the proportion of air mixed with the petrol vapour from the carburettor may be great, giving a “weak” mixture, yet one rich enough to be ignited in the cylinder. The throttle valve may be fully open and the spark advanced for high speed; the throttle partially closed and spark retarded for slow speed. Under these conditions the engine will run for an indefinite period without overheating. Up a steep gradient, the mixture may have to be made “richer” by partial closing of the extra air opening, and as more heat is evolved, the cylinder walls may become overheated, unless the engine power is sufficient to keep the bicycle moving through the air at a good speed. As the engine cannot run steadily at low speed, pedalling is resorted to for starting and for riding slowly through traffic. For this purpose, an “exhaust valve lifter” is usually fitted, by means of which the exhaust can be kept permanently open, in order to relieve the resistance to pedalling which the compression stroke would otherwise offer.

The nominal rating of the horse-power of a motor cycle engine is rather vague and indefinite. A 3-H.P. engine may have a cylinder of 76–80 mm. diameter and 76–80 mm. stroke. Twin-cylinder engines, with one crank, are largely used, and some excellent 4-cylinder motor bicycles are made with bevel gear transmission. The chief advantage of the multicylinder engine is the smoother drive obtained.

A “trailer” with two wheels for carrying a passenger can be attached to a motor bicycle, but the element of risk is increased. A side-car, with one additional wheel, forms a safer passenger carrier.

 BIDA, a town and administrative district in the British protectorate of Northern Nigeria. Bida town, situated in 9° 5′ N., 6° E., 25 m. N. by E. of Muraji on the Niger, is the capital of the province of Nupe. It was founded in 1859 when Fula rule was established in Nupe, is walled and of considerable size. In 1909 it was connected by railway with Baro, 40 m. S.S.E., the river terminus of the Northern Nigeria railway. The inhabitants, mostly Hausa, carry on an extensive trade and are especially noted for their embossed brass and copper work. The Bida goblets, in which brass and copper are beautifully blended, are of extremely elegant design. The town also boasts a glass factory. The preparation of indigo and the dyeing of cloths are other flourishing industries. The streets are planted with huge shade-trees, so that as Bida is approached it looks like a forest.

In 1897 there was a two-days’ fight outside the walls of Bida between the forces of the emir of Nupe and those of the Royal Niger Company, ending in the defeat of the Fula army (mostly cavalry). The victory was not followed at the time by a British occupation, and the defeated king returned after the withdrawal of the company’s troops and re-established himself upon the throne. In 1900 he allied himself with other hostile chiefs and adopted an openly antagonistic attitude to the British government. In 1901 it became necessary for British troops to march on Bida. The emir fled, without fighting, to Kano. Another emir was appointed in his place, and the province of Nupe was placed under British administrative control. Since that date the town has been peaceful and very prosperous. A mission school has been established, and is attended by the sons of the emir and of the principal chiefs, who are desirous of learning to read and write English. The administrative district of Bida includes the town and is the western division of the province of (q.v.). (See also : History.)