Go here:

http://software.bareknucklebrigade.c...it.applet.html

Take a few minutes to study this applet and play with it.

Most factory bikes come with a chain ring and cog ratio that provides about 78 gear inches.

For long commutes, I ride at 82 gear inches but find this too high, for me, when mixing with traffic.

The best all around ratio for casual riders seems around 72 gear inches, a little lower than most riders who start out on factory bikes think they like.

Those "in the know" generally describe 63 gear inches as the "do everything" street and mountain bike ratio, but this low of a gearing requires a VERY good spin, beyond the capabilities of many casual riders.

I presently ride at 61 gear inches and plan to move up to 65 gear inches in the near future.

Changing a tooth on a cog will result in a 3 to 5 gear inch change; whereas, changing a tooth on a chain ring will usually result in a one gear inch change; but play with the Rabbit applet and discover for yourself.