Last summer I had some particularly bad days, and I've been trying to discern the exact causes. Undoubtably there are a number of factors, but I've been wanting to run a particular idea by folks more knowledgeable in touring than myself.

I had this feeling that riding slowly (10mph or less average speed, stops not included) tires me out more than riding at 14-15mph, on a given route. All my previous tours, as well as training and commuting in the city, were faster than last summer, where I was solo and on some scenic routes. There was one particular 60 mile day when I gently climbed 600 feet over the latter half, and it took me less to ride 60 miles with 7000 ft of climbing back in 2012. The last 2 hours or so up the mountain pass at the end in 2012 were done at a staggering 3.2 mph, yet I still did better time. Food stops and rests were about the same.

What do you guys think? Is there an average speed sweet spot, so to speak, where the efficiency is better than it is above or below it? It's quite clear that one gets tired quicker when maintaining a greater speed than preferred, but I expected slower riding to have a positive, not negative, effect on energy levels at the end of the day, for a given route. Is it something universal, or could it be just me, because I train and commute at higher speeds and maybe I have conditioned the body to maintain a certain type of effort?