"Lex II: Mutationem motus proportionalem esse vi motrici impressae, et fieri secundum lineam rectam qua vis illa imprimitur." - Newton's Second Law from the original 1687 edition of the Principia Mathematica


Bicycle Gearing

            The purpose of a bike transmission is to transfer the power of the foot to the power that propels the bike forward. The force of the foot provides a torque which provides a tension on the chain which provides a torque for the back wheel. That torque provides a frictional force that propels the bike. The difference in radii between the foot and the front gear provides a mechanical advantage. The power is the same across the entire system but the amount of force and velocity adjusts resulting in the same amount of power.


chain drive
http://www.exploratorium.edu/cycling/images/chaindrive2.jpg


            For example, if a bicycle rider wants to get up a large incline but doesn’t want to destroy their legs, they can shift into a gear that lets them rotate the crank many times to turn the back wheel just once. This will result in more torque at the back wheel and the amount of force that the rider outputs is smaller at the expense of having to spin the pedals faster. The opposite is true if you are on flats and you want to travel faster. By choosing a larger drive gear and a smaller driven gear, the back wheel will have less torque but will complete more revolutions.

gears
http://www.exploratorium.edu/cycling/gears1.html

            Transmission systems of bikes are often discussed in gear ratios. If I had a front gear with 30 teeth and a back gear with 15 teeth it would have a gear ratio of 2:1. This means that for every revolution that I make on the front gear with my foot the back gear will rotate two times. Modern road bikes commonly have up to 22 gear combinations due to two front chainrings and 11 rear cogs allowing riders to select the most efficient gear ratio for their situation.




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A Brief Bicycle History

            The creation of the bicycle that we know today has three different steps in its history. The first and most important discovery in the development of the bicycle is accredited to Baron Karl von Drais because of his “running machine” which had two wheels and front wheel steering. His creation, the Draisienne, was improved on by many others into a pedal equipped bicycle, also known as a velocipede, which is the second milestone in the creation of the bicycle. More improvements to bicycles were made like rubber being added to the rims to improve comfort and tension spoking which allowed the front wheels to be made larger. Because the pedals were fixed to the front axle and gearing that we’re accustomed to wasn’t around, speed was limited to the amount of distance per pedal revolution. By creating a larger wheel, one could travel more distance per revolution and thus travel at a larger speed. These funny looking bicycles, commonly known as high rollers, were superseded by safety bicycles. These bicycles had a steerable front wheel, equally sized wheels, chain drive to the rear wheel, and a seating position in between the

A Brief Bicycle History

            The creation of the bicycle that we know today has three different steps in its history. The first and most important discovery in the development of the bicycle is accredited to Baron Karl von Drais because of his “running machine” which had two wheels and front wheel steering. His creation, the Draisienne, was improved on by many others into a pedal equipped bicycle, also known as a velocipede, which is the second milestone in the creation of the bicycle. More improvements to bicycles were made like rubber being added to the rims to improve comfort and tension spoking which allowed the front wheels to be made larger. Because the pedals were fixed to the front axle and gearing that we’re accustomed to wasn’t around, speed was limited to the amount of distance per pedal revolution. By creating a larger wheel, one could travel more distance per revolution and thus travel at a larger speed. These funny looking bicycles, commonly known as high rollers, were superseded by safety bicycles. These bicycles had a steerable front wheel, equally sized wheels, chain drive to the rear wheel, and a seating position in between the two wheels. Bicycle improvements continued to be made, but the creation of safety bicycles mark the last main milestone.

two wheels. Bicycle improvements continued to be made, but the creation of safety bicycles mark the last main milestone.