I second having a motorcycle history. Being comfortable on two wheels for me came from countless miles on four seperate motorcycles. On my second motorcycle, at 14 (the legal age in OK to have a motorcycle license) I hit 74 and thought I was king of the road, on my fourth bike, a '04 GSX-R 750 (the black and yellow one, 'cause it's faster) I've hit 176 on a track, of course. Once you've been that fast on two wheels, the speeds attainable on a bicycle seem like nothing. While you don't have to go triple digits on a motorcycle, riding one definitely helps to get comfortable with higher speeds on a bicycle.

-Barry-