Monday, July 9, 2007
This chart was sent to me by John Bravard from Portland, Oregon, where the bike lanes are plentiful and the rain is wet.
Here is some explanation from the gear-head himself. This is in reference to the numbers in the middle of the chart.
Johnny B. says, "It's 'gear inches' - which is a standardized measurement that basically determines how far the bike will travel with one revolution of the pedals.
The "46.4 inch" gear means that one turn of the pedals will move the bike the same distance as a wheel with a 46.4 inch diameter. The concept is that by introducing gears/gear ratios we effectively change the wheel diameter. I'm not sure why this is the standard instead of using the actual distance covered with one pedal revolution - which would be this number multiplied by pi.
Higher "gear inches" means that the bike will go further with each pedal revolution and that you will pedal slower at a given gear than if you were pedaling a lower "gear inch" combination. For example, if you were riding a 45 inch gear at 90 revolutions per minute, you would be traveling at approximately 12 mph. If you were riding a 90 inch gear at 90 revolutions per minute, you would be traveling at approximately 24 mph."
Well, there you have it. Thanks John!