Confusius: "Hi, I need to buy a tire and some gears."
Ken: "Ok. Road bike, Hybrid, or Mountain? How many speeds?"
Confusius: "Road bike. I'm not sure how many, my rear wheel was stolen."
Ken: "Ah, I see. Well the number of speeds on your shifter determines what cassette or freewheel you will need. (foreseeing trouble) Wait a sec. . . . do you already have rear wheel?"
Confusius: "No, but I have an extra front wheel."
Ken: "???"
Ken: "You know you can't put a front wheel on the rear, right? They aren't interchangeable."
Confusius: "Why not?"
Ken: "Uh. . . totally different. Different spacing, different hub shell, different axle."
Confusius: "They look the same."
Ken: "Actually they do not. The rear hub is wider and has either threading or a spline to allow you to mount the cassette or freewheel. Otherwise you'd have no way to bolt the gears on there(lamens terms)."
Confusius: "Oh. Ok, back to the drawing board." (he leaves)
