Originally Posted by Ken Cox
Go here:
http://sheldonbrown.com/gears/
Enter your correct tire size and crank length, and choose Gear Inches.
Put in a couple of different chainring sizes and a bunch of cog sizes (cassette) and click on calculate.
Study the results.
crank length dosnt make a difference in gear inches, you only need to calculate crank length with your for your gain ratio. I mean DUHHHHHHHHHHHHHHHHHHHH.