It just happens sometimes. You're tired; the legs simply aren't there; the wind feels stiff (although it isn't, really); and riding is a drag. I rode not quite 26 miles today, instead of 35-40. Maybe it's time for a break. The road bike is due for a tune-up, anyway, so this week would be a good time. I can ride the hybrid so I don't get too out of shape while the road bike is "out sick".