Bicycle Mechanics - can you explain gear inches?

i understand that the higher the gear inches, the harder it is to pedal thus the faster you can go. i've seen many charts and graphs and so on showing me how to calculate gear inches too. my question is what are the inches measuring? the length of the chain? the radii of the cogs/chainwheels? please help, i can't sleep at night with this weighing on my mind.

number of road inches you travel forward in one crank revolution of a gear.

thanks. i guess that's why wheel/tire size plays into the equation. i can sleep easy now.

number of road inches you travel forward in one crank revolution of a gear.

I don't agree. Since the equation normally used is:

diameter * teeth-in-chainring / teeth-in-cog

what you really get is the (effective) diameter of the drive wheel if you didn't have gearing.

To get the distance in inches traveled, you multiply the gear-inches by pi

number of road inches you travel forward in one crank revolution of a gear.

Good guess, but wrong.

Think back to the days of the high wheelers. In those times, bicycles were described by the diameter of the front wheel. The bigger the front wheel, the faster you could go provided, of course, your legs were long enough to turn the crank.

When the equal wheel sized, chain drive, "safety bicycle" was invented, riders needed a way to compare it's gearing to the high wheelers they were used to. Gear inches refers to the equivalent size high wheel diameter.

You are thinking of "gear development" usually expressed as metres of travel, not inches. Check out Sheldon Brown to find out more.