We have a story in today's Out There in the Gazette about the future of ski biking, which looks at the sweet, sweet bikes being made by a fellow named Devin Lenz in Ft. Lupton. They ride like a big downhill mountain bike, which is pretty cool. For a long time, the alternative ski bike has been something more like the bike below. Something that looks more like a kids toy that you ride using short foot skis like outriggers -- a lot of fun but silly looking.
Even if you're very good at it, like racers in the Alps.
So... ski biking, or skibobbing as it's also know, has never really caught on. But now there are a few people like Lenz making a more bike-like ski bike that seems to attract a lot of attention. Also, a company called Hansen (formerly Winter X Bike) makes these cool conversions for your existing mountain bike. I rode one recently, it was pretty cool. Not as design-specific as the other bikes, but also a lot cheaper.
So, if you really want to see what these bikes can do, get yourself some of this youtube of them in action at A Basin.