[QUOTE=FarHorizon]I'm about to put some "knobby" tires on my single-speed so I can have more traction in the dirt. Does using knobbies on the pavement wear them excessively? Also, I've read that the "V" profile of the knobbies should point forward on the rear tire and backward on the front. Is this so?/QUOTE]
Sometimes knobbies ride funny on pavement. Depending on the tires, the knobs can squirm in tight turns. I've never lost control due to knob squirm but it can definitely feel unsettling the first time that you experience it.
Years ago I read an article that suggested mounting tires with the tread arrows pointing toward the front on the top of the front tire and toward the back on the top of the rear tire. Some tires have directional arrows (sometimes more than one set) on them. Another guide that I sometimes use is to mount the tire with the colored label on the right side of the bike. It seems to me that there are a number of sometimes conflicting theories.