mtbdarby, I feel your pain. I've always been like that too, in every sport, which is why I always gravitated toward distance events -- whether it was competitive swimming, track or cycling. Sometimes it takes me about 10 to 15 minutes before my heart rate will stabilize and I get into my groove. I don't know why this is -- could be partly psychological, but I think it's also the way some of us are built (fast-twitch/sprint vs. slow-twitch/endurance muscle reaction -- at least that's how one of my swim coaches used to explain it.) Some of us are just built for the long, steady haul, some of us are quick out of the gate but short on sustained effort.

Anyway, what I do now is a whole lot of stretching beforehand and build in a 10-minute "pre-ride" before I get onto my favorite routes -- just flats, nothing challenging, and sometimes in areas with a bit more traffic. That way, by the time I get to the rolling hills around Boulder, I'm ready to GO! Just be patient with yourself. The hardest part is during organized rides, when everybody's shooting past me in the first 10 miles -- I have to hold myself back, not try to keep up. Most of the time, I'll be passing them by the time we hit the first hills. And that feels goooooood....