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| The first bicycles did not have gears. As in the one at
the left, all were direct drive. Each revolution of the rider's feet turned the drive
wheel once. Therefore the ratio of the rider's revolutions and the the drive wheel
revolutions was 1:1. In comparing one bicycle to another, the reference was the diameter of the drive wheel. The bicycle to the left has a 54" (inch) drive wheel. A bicycle with a larger drive wheel would go farther (or faster) with each turn of the drive wheel and a bicycle with a smaller drive wheel would travel less distance (or go slower) than the larger-wheel bike. This measurement of the drive wheel diameter became the standard measurement of bikes regarding its relationship to speed and distance. Therefore people would refer to their bike as having a 54", a 50", a 48", a 46" wheel, etc. Each bike however ONLY had one big wheel size, which had the advantage of going farther but harder to pump. |
| Then came the "Safety Bike", called such because
it put the rider lower to the ground. In the case of a single-speed bike, the relationship
between the "pedal wheel sprocket" (chain ring) and the drive wheel sprocket
(rear spocket) was changed from 1:1 ratio to a 2:1 ratio. Meaning that each time the rider
turned one revolution with his feet, the drive wheel in the rear, turned two times, or
twice. In this case with an "actual wheel diameter" of 27" (inches) the 2:1 gear ratio made the drive wheel the equivalent of twice that, or 54" (inchs), the same wheel diameter size as the Big Wheel Bike above, but with the safety of being lower to the ground in case of a fall. From there, bikes came onto the market with multiple gears, each having a different ratio and each resulting in a different EQUIVALENT DRIVE WHEEL SIZE, allowing the rider to select the best wheel size for the condition of the road he/she was traveling. |