Cycle Repairing and Adjusting
With a Chapter on building a Bicycle from a Set of Parts

CHAPTER VIII Variable Gear Devices The “Gear” of a Bicycle.—Before even the pur- pose of a variable gear device can be understood, the reader must have a clear conception of what is implied by the cyclist’s term “ gear.” It is not the dimension of any part of his machine, or even the number of teeth on either chain wheel or hub chain ring. It is a term that has descended from the days when the front-driven “ ordinary ” was the only bicycle in vogue. Then a machine was known as a 60-in., 56-in., etc., according as to whether its front wheel had a diameter of 60 in. or 56 in. respectively. A 56-in. wheel in one revolution travels (roughly) 176 in. ; and nowadays, when a bi- cycle, whatever its type, travels 176 in. per one revolu- tion of the cranks the gear is said to be “ 56.” A bicycle of 60 gear travels about 188| in. per one revolution of the cranks ; of 70 gear, about 220 in. ; of 80 gear, 251 in.; of 90 gear, 283 in.; and so on. The “gear” multiplied by 31 gives, roughly, the distance travelled by the bicycle per one revolution of the cranks, since the circumference of a circle equals, roughly, 3| times the diameter. Thus, the gear of a bicycle can be determined experimentally ; but it is more usual to arrive at it by a simple calculation : In the case of a chain-driven modern “ safety,” count the number of the teeth on the chain ii 8