As I written before, I'm just getting back into biking in a more serious way for the first time in 30+ years. A story I've seen many times in this forum's archives.
10 years ago I did a few 2-4 mile rides, two years ago I did a few 1-2 "rides." In September I decided to try it out again and really enjoyed the exercise from a couple of 3 mile rides. So I've been working my way up to 5, then 6, and then 2 days ago to 8.
However all of these recent rides were on unfinished trail beds that were a little soft. So on Tuesday I went onto a real rail trail to see what that was like. Tried out the Sugar River Trail out of New Glarus, Wisconsin --- a wonderful little town with good food, a great bakery, and two ice cream shops. And they have a great old train depot that serves as the visitors center and trailhead.
There were no cars parked at the trailhead parking lot, not unexpected on a weekday morning in late October. And I think they knew something that I didn't. For it had showed two nights before and was just melting off. I thought that wouldn't make a lot of difference on a "limestoned" trail. I was very wrong.
I rode for 3 miles and was dying. The trail bed was soft, very soft. My tires were cutting a rut about 1/4" deep in the trail, at times a 1/2" deep. The tires became caked with sand to the point where they were now "smooth" with no visible tread. It was like pedaling uphill the whole way, with 20 pound tires.
I turned and came back, riding 6 miles in all and was completely exhausted. Had to stop twice. I was very disappointed in my conditioning as I thought I had progressed to the point of where a 6 mile ride on flat terrain should be much easier.
So as I got back to town, huffing and puffing, I got on the town's paved trail. I had to try it out to see how much of a difference the trail surface made. To my delight, riding on the pavement, even after the 6 tough miles, was a breeze. I put in a couple of miles at a relatlvely good pace and renewed some confidence that my conditioning was improving.
So I found out, what I knew but guess I needed to have re-inforced, that not all miles are equal. I think the 6 miles on the soft trail were probably equal to 15 to 20 (or more) on pavement.