How important is it that you get your 100 miles? I came to a realization at some point that 100 miles on a road bike is not the same thing as 100 miles on my sturdy commuter. If I spent 7 or 8 hrs on a bike I could do 100 miles on a road bike but only 70 miles on my commuter. Either way it's 7 hrs on the bike at the same effort level. So I quit being so hung up on 100 miles. I focus on hours instead.