Richard from DC on 4/21/2018 3:22:58 PM:
From Harpers Ferry to Seneca Creek, the trail is mainly dirt. If it rains, it will be muddy for a week. Grass grows all on he towpath except for two strips where the bikes have killed the grass. From Seneca to Georgetown, the towpath is either compact dirt and sand or fairly large pebble stones. I ride it a lot. If it's muddy, even mountain bike tires have a tough time. And a mountain bike tires will absorb at least some of the shock of riding over he pebbles, and they'll get you through the loose sand and gravel. I've never tried it with my road bike except for a very short pebbled section, which rattles my teeth even on a steel frame. I have seen road bikes on the towpath, but they have larger tires. I think it's iffy in dry weather and impossible if it has rained.