development (~99 gear inches). Relationship to gain ratio Both "gear inches" and "metres of development" are concerned with the distance travelled per turn of the pedals, and are ultimately ways of indicating the mechanical advantage of the drivetrain, but neither of them take into account the length of the crankarm, which can vary from bike to bike. The crankarm is a lever arm. If two bicycles have different crank lengths but are otherwise identical, a longer lever arm gives a greater mechanical advantage. To take this into account, Sheldon Brown proposed a gear measurement system called "gain ratio," which is calculated by the distance travelled by the bike divided by the distance of revolution of the pedal axle during one turn of the crank. He argued that it also has the advantage of being dimensionless. See also Bicycle gearing Derailleur gears Hub gear Outline of cycling References External links Sheldon Brown's gear calculator Online calculator for gear inches, metres development, and gain ratio BikeCAD has a graphical means of displaying gear inches as described here Gain Ratios—A New Way to Designate Bicycle Gears Gain and Watts Calculator Mike Sherman's gear calculator Online calculator for derailleur gears, with useful graphic displays HPV Drivetrain Analyzer A drivetrain analyzer and gear calculator for HPV's (Human Powered Vehicles) that will handle compound drives and geared cranks and hubs. Bicycle gears