Originally Posted by Cornbread
I usually commute on my cheap MTB because I would have to lock my road bike up outside which I don't want to do. I think the best and cheapest thing you can do is make your MTB more efficient. This is what I did. Get slicks for your MTB, those big knobbies really slow you down. Something like this.
http://www.nashbar.com/profile.cfm?c...eid=&pagename= Also, make sure your seat is high enough to properly extend your leg. Most cheapie MTB seat stems don't extend very high and so you don't use all of your legs like you could. I had to get a new, longer, seat tube that fit me properly. I actually lean over pretty far more like a road bike than the typical upright position you see on a MTB.
Dito for my mtb - I run 1' or 1.25" slicks and use it for commuting but also on slow long road rides and it is quite adequate. I will mention mine cost more and is probably a better frame & wheelset overall, and also that I do prefer a road bike for longer rides but I set my mtb and road bike to have more or less identical positions, regarding the contact points (seat, peds, bar).
So if you like your mtb, try the higher pressure narrow tires and fiddle with your seat/handlebars to get a more aero position. If you want to go nuts you can get a drop bar for your bke (just make sure the new bar will fit your stem clamp and accept your brake/shifters); it's prolly cheaper to just throw on bar ends if you don't have them already. You'll want different hand position options on longer rides.
Have fun!