I just got back from Yellowstone, and the roads leading to it. All I can say is that if you leave the bike home, you'll be kicking yourself every day. It is some of most beautiful country up there, and there were lots of cyclists around. In Yellowstone itself, most roads seemed bike friendly, although some sections didn't have much shoulder, but these sections were short. The roads through the Tetons was also incredible. It seemed that wherever we went, we were thinking how bike-able the roads were. Have fun!

(Oh - in Yellowstone, we saw a few bears, but they were far off the roads - unfortunately on our hiking trails , and the bison didn't really seem to care about our presence.)