When pedalling gets too easy, switch to a higher gear. When it gets difficult, switch to a lower gear. That's it in a nutshell.

Reality: a road bike will be faster than a mountain bike minus other factors. The slicks are nice, but there is nothing like a lightweight, aerodynamic bike with skinnies when it comes to speed on the roads. With your mountain bike, you will have more "rolling resistance" than your sister does. If you want to go faster on the road, get a road bike.

As a mountain biker, I would then suggest that you put the knobbies back on the bike and take that puppy out on some trails! Oh, yeah! I like road biking, but the mountain biking helps me work out a lot of stress, but I'm a more aggressive personality.

Enjoy!