There was extensive coverage about fat bikes in the media last year (it's hot) and there's a photograph of a person riding a fat bike towing a Christmas tree on the cover of this year's Patagonia Holiday Catalog. Fat bikes were recently dubbed the "Hummers of the two-wheelers' world" in the Wall Street Journal. These specially-made bicycles that accommodate ultra-wide tires that can be run at very low pressure less than ten pounds of pressure allow fat bikes to roll over soft, slippery surfaces like snow. XC ski areas from Vermont to Michigan and Arizona to California and Washington are now allowing fat bikes also called snow bikes to be used on their groomed trails and offering rental bikes, too.

Fat bikes are one of the fastest growing segments of the bicycle industry. There were 10,000 fat bikes sold since 2010. They provide a great way for cyclists to stay in shape during the winter season. In eastern Washington's Methow Trails the winter season can be longer than all other seasons combined and it was one of the first trail networks to embrace fat biking. They saw it as a new, exciting way to get outside and recreate and for the passionate XC skier interested in fitness, it provides another way to cross-train. Last winter, there were 500 rentals with only 16 fat bikes at Methow Cycle & Sport and this was an increase of 60% above the previous year.

Kingdom Trails in northeastern Vermont is a foremost mountain bike destination in the east and they've quickly parlayed this notoriety into becoming a mecca for fat bikers in the winter. They host the biggest fat bike festival in the east.

Fat bike products are available from companies such as Surlybikes.com and Salsacycles.com and even the mainstream company Trekbikes.com among others.

According to a recent survey by the Cross County Ski Areas Association there are at least 28 of the XC ski areas, which now welcome fat bikes on their trails. Flagstaff Nordic Center outside of Flagstaff, AZ is running a snowmobile on 25 km of the snowshoe trails to accommodate fat bikes. The bikes ride much better on packed trails compared to riding on soft snow. Fat bikes can be rented at Flagstaff Nordic for $35 on weekends plus a $10 trail fee, and they offer a 40% discount on weekdays ($20) while charging a lower trail fee on weekdays ($7), too.

One avid snow biker describes the thrill of riding his fat bike in the winter as, "Riding on snow has been a great alternative to my other winter love…Nordic skiing. Hopping on the snow bike has been a great way to mix up the winter activities. There's an amazing sensation when you climb aboard a snow bike and find that you "can" ride where only skiers or snowmobilers had once been able to go!" Surveys show that 71% of fat bikes were introduced to the sport at a demo, borrow, or rent the bike that they are riding. And 64% of the fat bikers said they would pay to ride on groomed trails.

Fat bike trail offerings are assessed on a day-by-day, snow conditions, user compatibility basis. Information on the trails that are open to fat bikes is available daily on the Methow Trails grooming report. Just like a skier, a valid Methow Trails day pass will be required for snow bikes.

Fat bikes are available for rent ranging from $10 at Rikert Nordic Center in Ripton, Vermont to $20 during the week at Flagstaff Nordic reaching $75 a day at New World Sport, a Fort Collins, Colo, shop that sends riders to local packed snowshoe and XC ski trails. It's $55 at Village Sports Shop in Lyndonville, VT and they suggest rider use the bikes on the nearby Kingdom Trails, where there are bikes to rent, too. Methow Cycle and Sport in Winthrop, WA has a $35 half day rate or $55 for a full day. They have rental bikes at the store and on site near 5 km of trails at nearby Sun Mountain Lodge. Reservations are recommended for weekends and holidays. Methow Cycle and Sport will also provide rack adaptors for customers who wish to transport rental fat bikes to the riding area of their choice. Other XC ski areas that have fat bikes on location to rent include Cross Country Ski Headquarters in Roscommon, Mich at $15 per hour and California areas with fat bikes include Bear Valley Cross Country & Adventure and Royal Gorge Resort where there are 10 km of trails available and rentals for $20 per hour.

As one might imagine the price for purchasing a fat bike ranges greatly from a low-end of $200 (at Walmart) to $2,000-6,000). Like any other equipment the low end is probably less reliable and the high end includes bells and whistles or are built with carbon fiber construction.

Currently, the issues for fat bikers include skier/biker relations and conflicts, variable and changing snow conditions, impact on trails, and building fat bike-specific trails. Fat bike riders are asked to follow a code of etiquette because they can damage trails groomed for classic and skate XC skiers. A typical list of XC ski area "conditions of use" include:

* Riders need to purchase a trail pass to use the area's trails and tell the ticket vendor that they are planning on fat biking.

* Trail access is dependent on conditions and they should check the daily grooming report for detailed trail access information.

* Purpose built snow bikes only! Both tires must be wider than 3.7" and tire pressure must be less than 10 psi, no exceptions!

* Bikes should yield to all other users. Stay to right side of trail at all times, stay out of the classic ski tracks, and give skate skiers a wide berth. * Stay off trails with more than 3" of new snow.

* If you are leaving a rut deeper than an inch, having a hard time riding in a straight line, or pushing your bike, the snow is too soft and you absolutely should not be biking on the trails.

* Be an ambassador for the sport – stay polite, educate other bikers, discourage bad behavior, follow the rules, and we'll all have a good time this winter.

* Stay on trails designated for Fat Biking.