I ride my mtb on the road, and generally average 13mph. The roadies (men) always smile and nod. I wear tights and a jersey...there's something about fat bottomed girls... we make the rockin' world go round .

You might consider putting some slicks on if you aren't going to hit any dirt for a while. Or get some semi-slicks which go both ways as long as you don't need too much traction.

Have fun, and think of all the extra calories you are burning lugging the extra mtb weight...