# Bicycle Mechanics - gear inches

Bikeforums.net is a forum about nothing but bikes. Our community can help you find information about hard-to-find and localized information like bicycle tours, specialties like where in your area to have your recumbent bike serviced, or what are the best bicycle tires and seats for the activities you use your bike for.

View Full Version : gear inches

ogbigbird
10-26-08, 02:52 PM
i was trying to remember the formula for figuring out "gear inches". i remember it's something like chainring multiplied by wheel or cog size, divided by something else. if someone could give me the formula to figure this out, that would be swell.

pt2 of my question, is that not only do i have bikes with conventional 26x1.75/2.125 wheels, but also a few 26x1 3/8. since these are two different wheel sizes in reality, what numbers do i plug in for the 26x1 3/8 wheel vs the conv 26' wheel. and what exactly is "gear inchs"? i used to know this formula, but that was a long time ago. thanks

Galoot
10-26-08, 02:55 PM
5 seconds of googling:

http://en.wikipedia.org/wiki/Gear_inches

merlin55
10-26-08, 03:17 PM
.01 seconds of memory: (Chainring teeth/cog teeth) x wheel size in inches (eg. 27 or 26 or whatever)

39/13 x 27 = 81 inches

ogbigbird
10-26-08, 03:29 PM
thanks! took it a step further and used sheldon's gear calculator.

wmodavis
10-26-08, 05:03 PM
http://sheldonbrown.com/gloss_g.html#gearinch
http://sheldonbrown.com/tire-sizing.html

+1 galoot