I also wonder about the mileage per hour number - average on a bike computer or when you look at the speed. It seems that when I am riding on flats, it's usually between 13-14mph when I look down, sometimes can be more. Downhill can be 20-30mph. But there are so many steep hills where you see 5-6mph going up, that when I'm done, the average is usually 11mph and I can't seem to get above that.

I just finished a bike tour where I was the slowest one in the group and felt very frustrated and discouraged. The others either have been riding much longer than I or were much younger than I. I think it may be good to stretch yourself with someone who is slightly better than you, but being with a group that is too fast doesn't help.

I did learn that the mileage was not the key. I could feel good or bad after 30-40 miles depending on the speed of the ride and if there were any breaks. If we rode half way, had lunch and continued, I was fine. If the group rode straight thru, I barely made it back. I also just ordered a bunch of Nuun electrolyte tablets for my water because I sweat a lot when it's hot out and may have depleted my salt.