Riding around last night, I was feeling like I was getting more winded riding my road bike than I would have riding the same distance on my mountain bike. I guess it makes a little sense: slightly different muscle groups being worked with the different handlebars and different, er, stride? Stroke? Yeah. Or perhaps given a new maximum speed I'm expending more energy maintaining that higher power output.

That, or maybe it's just that I can now hear my breathing, whereas before it was drowned out by the angry buzzing of my mountain bike tread.