I was stopped on the side of the bike path, topping off a slightly underinflated tire. “Hey nice bike. What’s that extra tube for? Must be heavy duty or somethin’. Is it for extra weight?” The tube in question is the twin top tube on this here Kona Humuhumu. A retro/cruiser/mountainous/classic/singlespeed/bar-hopping/klunkish/commuter. Why is the extra ...