Originally Posted by
wunderkind
Part of my commute is street and packed gravel. I've researched around and determined that while getting smoother tires will help me to go faster on the streets. But may be a risk on the gravel paths (has turns and slight humps). So i am wondering if it make sense to have the front tire remain knobby but the rear will have a skinnier smoother tire. Does it make sense or am I off the wall here.

Ha! just last week i was wondering about the same question
http://www.bikeforums.net/showthread.php?t=557699
apparently as they said, it's not going to make much of a different, is either or.
mixing both doesn't really do anything.
specially for me, i cut across large grassy fields (short cuts

) and if i use the skinnier tire on the rear it will sink me into the dirt.
using the fat tires (Racing Ralph) i've no problems on those places.
the only downside of using fat tires, is not so much for performance, but the noise and breaking ability on asphalt road.
the Racing Ralph is pretty damn fast compared to Knobbies tires, the only problem is stopping on target, sudden stops with Knobbies type of tires are usually impossible on Asphalt roads, while racing tires can hit it on the spot, if you can manage not to go flying off your handle bars
just today i had a close encounter stopping suddenly for a cross road that suddenly lit up as i was aproaching, a long streak of squealing sound... my poor tires .... sigh...