This last fall (October) a friend and I participated in the 19th annual Yellowstone Bike Tour. Who puts it on just flew out of my brain, but they sponsor a spring ride in May as well. We ride from West Yellowstone, Montana in to Old Faithful for thirty miles, then back if one desires. There is limited sag support. I mean they do have several vehicles that keep an eye on the riders and will help with any mechanical problems, but they don't have much in the way of food. My friend and I just packed our own goodies and didn't have any problems at all. I did the full ride and it came out to a bit over sixty-two miles. My friend, a beginner, called it quits at the halfway point. The elevation varies from 6200 feet to around 6700 feet and can be a problem to those not used to it. Going in to Old Faithful seems to be more difficult, as the ride back went rather smooth despite a headwind. There is still the normal park traffic to deal with, but in early October it isn't too bad. There isn't a time limit on when one has to finish and some take all day! We just took it easy and enjoyed the beautiful scenery, the buffalo along the side of the road, the steam from the geysers and the wonderfully pine scented air. There is a free spaghetti feed the evening after the ride for tour participants and we found it to be rather lacking. (Cold noodles and not enough bread and salad.) If anything, that would have to be my only gripe. Other than that, cool ride, awesome scenery, a long-sleeved tee and good company made for a good ride. I am thinking of doing it again this year.
The park also opens the roads to bikers only once they plow the snow off. This is usually a few weeks before they offically open the park.