The sidewalks here are too rough for my road bike. The bumps will beat you up on a skinny tire. I can only do about 10-12mph vs 18-20 on the street next to it. MTB tires may not be as bad. It all deals with your personal comfort level with the road and if they enforce the no sidewalk law. Most of the time, here anyway, as long as you are going in the same direction of traffic it is okay. If the road is real busy, there is a section I will ride the sidewalk, but I hate it. It would probably cut your time in about half if you use the street only.