Bicycles & tricycles; an elementary treatise on their design and construction, with examples and tables by Sharp Archibald 1862-1934

Author:Sharp, Archibald, 1862-1934
Language: eng
Format: epub
Tags: Bicycles, Tricycles
Publisher: London, New York, Longmans, Green
Published: 1896-03-25T05:00:00+00:00

These principles are of direct application to the gearing of cycles.

Example I.- Suppose two rear-driving bicycles each to have 28-inch driving-wheels geared to 56 inches; let the bicycles be equal in every lespect, except that in one the numbers of teeth in the wheels on the crank-axle and hub are 16 and 8 respectively, while in the other the numbers are 18 and 9 respectively. When going along the same gradient at \k\^ same speed, the speeds of the chain relative to the machine are in the ratio of 8 to 9 ; consequently, the pulls on the chain will be in the ratio 9 to 8, that on the chain of the bicycle having the smaller wheels being the greater.

Example II. —Let two bicycles be the same in every respect, except that in one the cranks are 6 inches long, in the other 7 inches. When running along the same road at the same speed, the work done in overcoming the resistance will be the same in the two cases, and, therefore, the work done by the pressure of the feet on the pedals is the same in both cases. But the pedals' speeds are in the ratio of 6 to 7, therefore the average pressures

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to be applied to the pedals are in the ratio 7 to 6, the shorter crank requiring the greater pressure.

Example TIL —Suppose two Safety bicycles to be equal in every respect, except that one is geared to 56 inches, the other to 63 inches. With equal riders, running along the same road at the same speed, the work done in both cases will be equal. But the distances moved over during one revolution of the crank are in the ratio of 56 to 63, that is, 8 to 9. The numbers of revolutions required to move over a given distance will therefore be in the ratio of the reciprocals of the distance—that is, 9 to 8. Consequently, the average pressures to be applied to the pedals in the two cases will be in the ratio of 8 to 9, the bicycle with the low gear requiring the smaller pressure on the pedals

The whole question of gear for a bicycle thus resolves itself into a question of what will suit best the convenience of the rider. Assuming that the maximum power of two riders is exactly the same, one may be able to develop his maximum power by a com. paratively light pressure on the pedals and a high speed of revolution of the cranks, the other may develop his maximum power with a heavier pressure and a smaller speed of revolution of the crank-axle. The former would therefore do his best work on a lower geared machine than the latter. The question of length of crank depends also on the same general principles, different riders being able to develop their maximum powers on different lengths of crank.

The maximum power a rider can develop by pedalling a crank-axle is probably at low speeds

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