Are you aware that in May of this year Adventure Cycling will release route maps for a new Chicago-NYC route? You can see it here in blue:


https://www.adventurecycling.org/rou...rview-map-pdf/


What I think we be called the Philadelphia Spur goes through Pittsburgh then uses the GAP and a portion of the C&O. It eventually intersects with their Atlantic Coast route west of Lancaster, PA. The Atlantic Coast route goes through D.C.


What width tires exactly? As noted you could very well be fine on the GAP. From the southern terminus of the GAP at Cumberland, MD, you could take U.S. 220 and 220(Bus.) to Bedford, PA (original home of Cannondale) to pick up signed PA Bike Route S. That will take you east to an intersection with ACA's Atlantic Coast route in/near Columbia, PA. I did this during a cross-PA tour back in 2013, although I continued east to Philly. Not the most direct route, but it avoids the C&O, and there are enough camping options on or close to the route to make it workable. Another benefit is that you could detour off Route S at Breezewood, PA and ride the Pike to Bike, which is an unofficial 8.5 mile trail on an abandoned section of PA Turnpike. Not only does it eliminate a big climb out of Breezewood, it's a neat ride assuming you have lights for the two long, unlit tunnels. (IIRC, the second tunnel heading east is over 1 mile. There is a crown near the eastern portal so you literally cannot see the light at the end of the tunnel until you close in on it.) It was one of the filing scenes for the post-apocalyptic film "The Road" staring Viggo Mortensen. The surface is somewhat rough in places, but I had a friend who rode it last fall on 25c tires during a credit card tour and was fine. From the end of the trail it is extremely easy to get back on Route S.


Let me know if you want details.