 Suggested Gearing Written by John Bryan 45 inch gear for Advanced Riders At least a 35 inch gear for Tourist or Beginners. Flat Land Riders - take note of the climbing chart ! This course will get your legs if you are not ready! Inch-Gear Calculations Explained Here is the way to calculate the in-gear on a bike: Divide the front chain ring teeth by the rear cog teeth and multiply by the wheel size. For convince on a road bike we use 27" for the wheel size, a mountain bike may use 26", or in the case of a small bike 20" tire you would use 20". Example:   39 front divide by 26 rear x 27 ( road bike ) = 40.5 inch-gear If you multiply the in-gear by the constant (pie ) 3.1415 , you will get the distance traveled in inches, with one complete pedal revolution. The lower the in-gear, the shorter distance traveled per pedal revolution, but it is easier! Example:  40.5 x 3.1415 = 127.23 inches (Bike travels with one complete pedal rev) You can see by this that the smaller the in-gear the more mechanical advantage you have, but the bike speed or movement per pedal revolution drops. Note: The wheel size is not a consideration when computing the distance traveled with one pedal revolution. It is only brought into consideration when calculating the in-gear. The number 27" for a road bike is approximate since tire sizes vary and today's bikes use 700 C wheels. The change is so small most folks don't worry about it.  Incidentally, if you know the in-gear and the pedal revolutions, you can calculate the bike speed as follows. In - Gear x Rev (RPM ) x Pie (3.1415) divide by 12, divide by 88 ( this gets you to MPH) equals speed in Miles per hour.   Example going up Mitchell in a 40.5 in-gear at 60 rpm pedal speed: 40.5 x 60 x Pie ( 3.1415) divide by 12, divide by 88 = 7.22 MPH. :-) John