Originally Posted by Yoshi

But let's say that you ride a bike geared at 48x16. Someone rolls up with a bike geared at 48x16. Are you pushing the same gear? If the person's wheels are a different diameter than no, your gearing is different. And what about that guy riding 39x13? Is it immediately obvious that he's riding the same gearing, assuming that you both have the same size wheels/tires?

Gear inches make comparisons easier. Instead of saying "I ride a 47x16 with 700x23C tires" I can say "I ride 77 gear inches." You tell me which is easier.