Last summer, I rode the southern Illinois Tunnel Hill Trail (to see the eclipse!) 77 miles round trip that day (with a long stop in the middle). A small section of the trail was paved, the rest was crushed stone, with a few sandy sections.

This ride was a lot more effort than riding on roads. On this flat trail, I was averaging about 11 mph instead of 15 mph on the road. I had 35mm small knob tires with a smooth block center section for pavement. After this ride, I bought some 38mm all smooth tread tires, thinking they would "float" better on crushed rock trail surfaces, and need less power.

Even hard packed trails like the GAP take more power than riding on paved roads.

So, you might consider a 60 mile trail ride to be more like an 80+ mile road ride. It would help if you can do a test ride this spring on an unpaved trail -- to see if you want to cut back the daily mileage on the GAP.