The Gap is great, extremely well maintained. The C&O is nice,but suffers from poor maintenance. ( the Gap is maintained by volunteeers, the C&O by the National Park Service.
I would ride the Gap on road tires every day. We were on a tandem with 42 gravel kings. I was jealous of people on race bikes flying by on the Gap. Glad we had the 42’s on the C&O.
Given the quality wide tires you can get now, I would pick something like a Continental 5000 32 mm tire for the Gap. I’d have no hesitation to ride it on 25’s on my road bike that can’t fit any bigger.
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.