thats what I am doing.I have my mtn bike for when I go camping or riding with the family.then I have a very old road bike that I am fixing up to ride when I am by myself.that way I can get the speed up to where I want and enjoy it for the ride.(not that I don't enjoy my rides with my family.)I can go farther and faster by myself that with the family.it is not the greatest old bike but it's paid for.keep the mtn bike.put some slick tires on it.I did and it really changed the way the bike rode.
Rick G