Originally Posted by The Fixer
...that's fuzzy math.....
*shrug*
Far be it for me to contradict Sheldon Brown.
"...to calculate: the diameter of the drive wheel, times the size of the front sprocket divided by the size of the rear sprocket."
Diameter of the drive wheel changes your gear inches. 700c wheels have a different diameter than 27inch wheels. QED.
http://www.sheldonbrown.com/gears/