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Take Advantage Of Custom Configuring Gears --- Through Understanding And Simple Math

The Information Presented Below Can Be Used To Take Advantage Of Custom Configuring Gears For A Particular Bike Application!  Design Your Perfect Set Of Gearing For Your Adventure Bike, Sport Touring Bike, Commuter, Getting The Best Peddling For Your Type Of Riding, Needs, The Expected Riding Terrain, Loads Carried, And Weather Conditions.

Bike gear measurements include: sprocket-size, gear ratios, gear inches, meters development and gain ratio.  Gear measures are meant to be simple, practical, calculations.  Gear measures are relative to a bike's cadence, speed, gradient and terrain handling.  Differences and inaccuracies arise between inch and metric users, and the fact that many wheel sizes are nominal and not actual accurate sizes.

Sprocket-Size referees to the number of teeth of the two sprockets on a bike; the front chainring gear, and the rear cog gear.

Example: a bike with a 42-tooth chainring (front sprocket), and a 17-tooth cog (rear sprocket, has what bike engineers would say is a "42 17" sprocket-size.  This is often written down as 42 x 17.

Gear-Ratio is the basis for other gear measures. It's the relative measure of crank to wheel rotation, as each turn of the crank results in so many turns of the wheel. On a chain-drive bike, it's the number of teeth on the front chainring divided by the number of teeth on the rear cog.

Example: A 42-tooth chainring and 17-tooth cog (42/17) has a 2.47 gear ratio.

Gear-Inches is the formula commonly used by English speakers. It's a nominal measure of gear ratio times drive wheel diameter in inches, and derives from high-wheelers who referred to wheel size by diameter in inches, saying "I ride a 56-inch wheel." A standard 27-inch wheel bike with a 42/17 sprocket combination (2.47 gear ratio) has 66.7 gear inches.

Development is the term for Metric system users to define the distance traveled in one pedal rotation, measured as gear ratio times wheel circumference in meters. A bike with a 42/17 sprocket (2.47 gear ratio) and 700c wheels (2135mm circumference) has 5.27 meters development.

Rollout is the best way to measure wheel circumference. In bike racing, it's the official way to regulate development. Instead of measuring wheel circumference by multiplying pi (3.14) to wheel diameter, it's more accurate to do a rollout of the distance of one wheel rotation, with a cyclist mounted on the bike with properly inflated tires. To measure meters development, rollout is the distance the drive wheel travels in one crank rotation.

Gain Ratio is a new measure, a pure ratio that calculates wheel radius divided by crank length times the gear ratio.  A road bike with 700c wheels (340mm radius), 170mm length cranks, and a 42/17 sprocket combination (2.47 gear ratio) has a gain ratio of 4.94.

It Is Easier To Convert Millimeters To Kilometers Than Inches To Miles.   Learn Metric And You Will Have A Easier Time With Measuring, Distance Concepts, And Come Up To Speed With The Rest Of The World!