A few years ago, when mountain bikers on fat-tired bikes first ventured into the Minnesota woods, a group of guys went online to share their best tips for making the trails ridable. Despite the 4-inch-wide tires that give fat bikes their distinctive, almost cartoonlike appearance, the bikes still sink in deep snow. Opting instead for a packed trail, some of the guys said they should just send masses of volunteers outfitted with snowshoes to stomp out a path and hope fresh snow didn't fall before they got to enjoy it. Others were more — and often less — practical, suggesting a snowmobile, a motorized snowboard or even using buckets of water to create an icy path. One guy suggested some combination of blowtorch and a snowmobile.

It wasn't entirely clear if he was joking.

That was just a few winter riding seasons ago, but since then fat biking has turned a corner. Riding a crest of surging sales, bike shops report running out of the $1,600 to $4,500 bikes as ridership has grown by about 50 percent nationally each of the last two years, according to an industry presentation from Quality Bicycle Products (QBP), a major bicycle parts supplier based in Bloomington.

Some 20,000 fat bikes are in ­circulation in the U.S., many with tires ranging from 3.7 to 4.7 inches wide, enabling them to roll down snow-packed trails, across beaches and frozen lakes and in a surging crop of new races and organized rides designed specifically for people who want nothing more on a freezing, snowy day than to hop on a bike and go.

"It seems like everyone has a fat bike nowadays," said Reed Smidt, president of Minnesota Off-Road Cyclists (MORC), an advocacy and bike trail building group.

Smoothing the way

If this is fat biking's moment, then the volunteer trail workers and groomers have made much of it possible.

Some 50 miles of groomed fat biking trails, known as single-track, are now offered at six parks in the metro area.

Each trail has its own grooming regimen, said Smidt. Some get groomed by machines, others by snowshoes. Some just get ridden on by other fat bikes until there's a path.

The hodgepodge of grooming ­methods, some of them made possible by clever hacks, gave rise to the first-of-its-kind snow grooming summit in Cable, Wis., on Jan. 10. Sponsored by MORC and QBP, the conference drew some 70 people from across the Upper Midwest to share their best tips.

"We wanted it to be like show and tell," said John Gaddo, a QBP employee who helped organize the conference. Photos from the event show a lineup of the various grooming machines people brought to show off. Unlike the 4- to 7-foot-wide grooming devices used for Nordic ski trails, fat bike groomers must be narrow enough for single-track bike trails, which are sometimes as narrow as 20 inches.

Some groomers use "rollers" that are little more than heavy cans laid on their sides and rolled down the trails. Others use "draggers" that sculpt a flattened path as they're dragged along. Providing the necessary horsepower for either method sometimes falls to a snowmobile, but the machines often can't maneuver through tight, twisting turns commonly found on single-track. So other groomers use a Rokon, an off-road motorcycle with two-wheel drive made by Rokon International of Rochester, N.H. Designed to go into the back country, it's a low-geared, low-speed motorcycle, which happens to do a good job pulling grooming devices, said Gaddo.

Gaddo said he's a fan of both rollers and draggers, rollers for their efficiency and how well they pack the snow, and draggers like the one he calls "the cheese grater" for its appearance because it keeps the snow fresh and prevents the trail from icing up.

Wide smiles on fat bikes

As a longtime bike commuter, I'd ridden in the winter before, but never on a fat bike. The big tires seemed like overkill and for the last few years I found myself watching fat bikers with something bordering on disdain. My 1961 Schwinn Typhoon rolls easily in winter over a plowed road or bike path, and pride kept me from trying anything new. And then, during a recent warm winter day, a friend encouraged me to come ride with him at Elm Creek Park Reserve on one of the winter biking trail systems maintained by the Three Rivers Park District. Another friend loaned me his beautiful fat bike made by Salsa, one of the brands owned by QBP.

We parked at a lot near the trails and rode up a plowed road for a few minutes. The tires made a satisfying sound as they rolled with sure-footed stability under the frame. The bike itself felt similar to any other mountain bike, but the tires were deflated to just 6 to 7 pounds of air pressure. It's a common tactic for fat bike riders, giving them more stability as the tire flattens out where it meets the road. We saw an opening in the trees, the beginning of the trail, and I drove straight in.

And this was where my first lesson in fat bike riding kicked in: Warm weather left the trail's shoulders soft that day. As long as I stayed in the trail's middle, the bike did fine, but winding through the woods around trees, I often strayed to the trail's edge. If I went too far, the front wheel sank and the bike came to a sudden stop.

Other times, some funny things about momentum took place, and I found myself riding a runaway bike that didn't respond to my steering. Even with the handlebars turned and the front wheel pointed toward the middle of the trail, the tire sometimes slid down the side of the hard-packed ridge left by other riders and the bike followed its own course deeper into the woods, dropping me on the trail.

Soon I realized I didn't have the skill to ride the bike in these conditions, even with a lifetime of bike riding behind me. Other riders out that day swiftly navigated the trails I struggled on. It was just the challenge of it that made me wonder: What have I been missing?

The trail improved somewhat, and so did I, and I managed to wind through a loop's worth of wintry woods before arriving back at the parking lot. I returned my friend's bike with the idea I'd go out again, once it got colder.

A week later, I borrowed a Pugsley made by Surly Bikes, another brand from QBP. It's one of the original fat tire bikes, introduced in 2004 as the first mass-produced fat tire frame, and likely the reason fat biking has taken off. On a brutally cold January day, the groomed trail at Theodore Wirth Park in Minneapolis was more ridable. ­Slicing through the trees as cross-country skiers enjoyed their own trail nearby, the Pugsley rode the snowshoe-packed trail as if it were a dirt path in the summer. A few times the trail emerged from the woods and crossed in front of skiers, a sensation I started to enjoy as the summer world of biking and the winter world of ­skiing collided.

Later that day, with the world of fat biking opening up to me, I found myself riding down the frozen waters of Minnehaha Creek. For whatever reason, there wasn't much snow on the creek and dozens of fat bike riders before me had left tire marks up and down the route. The Pugsley rolled easily along the creek's meandering path, under bridges festooned with icicles and past snow-covered back yards. After an hour of traveling west, I turned and pedaled east, eventually arriving at Lake Hiawatha. The snow here was deeper and it took effort and balance to push through, but something about riding a bike through the snow across a frozen lake made me laugh. Smidt, the MORC president, had warned me: People sometimes get a big grin riding on fat tires.

Near the middle of the lake I stepped off the bike and took in the view. Ice crystals moved in shimmering rivers across the snow. Wind filled my ears with a low howl. And the Pugsley, riderless but still upright with its fist-width tires locked in inches of snow, pointed toward the shore.

It looked perfectly at home.