MCCALL, Idaho (AP) — You’ve probably seen these in a bike shop, in a bike rack, or even hanging from the ceiling of a bar or restaurant and wondered, “What the heck is that?”

They’re known as “fat bikes,” rather than “fat tire” bikes, which was an early nickname for all mountain bikes.

Fat bikes sport oversized balloon tires run at low air pressures that are specially designed to ride on packed snow and other surfaces.

So what’s it like to ride one? In short, it’s like riding a bicycle. There’s no special technique involved. You just get on and ride, and that’s what makes them fun.

While they’re sometimes called “snow bikes,” they’re actually more versatile and used for all kinds of riding, from snow to sand to commuting.

Kathy Muench of McCall and her husband, Steve, were looking for another activity to do during winter, and a pair of fat bikes caught their attention.

“We were pretty excited from the get go,” she said. “You look at these things and go, ‘Oh my gosh, look at that bad boy.’ “

They started riding on snow — both groomed cross-country trails and snowmobile trails — then branched to frozen lakes, firm snow during spring, as well as dirt roads, singletrack and even beaches.

“The more you’re on it, the more fun it gets,” she said.

On a recent weekend, it was the trails at Jug Mountain Ranch near McCall that lured them back onto their bikes.

“We’ve been on our bikes more than we’ve been on our skis this winter,” Kathy said.

I borrowed Jug Mountain Ranch manager David Carey’s bike and joined them on the trail system about 2 miles east of Lake Fork (For directions go to jugmountainranch.com/location.)

Carey has welcomed the bikes on Jug Mountain’s groomed trail system, and he’s experimenting with a smaller, narrower groomer that compacts some of the ranch’s singletrack trails so they can be used during winter.

Carey sees fat bikes as another opportunity for winter recreation, a way to extend the bike riding season in the McCall area, and another way for people to enjoy Jug Mountain Ranch’s trails.

All riders have to do is buy a $10 daily trail pass and ride the ranch’s 15 miles of groomed trails and additional singletrack when conditions allow.

“Adding the fat bike to the overall Jug Mountain Ranch trail experience is a great fit,” Carey said. “We are firm believers that this is not a fad and can significantly increase winter trail use to a new demographic.”

Carey rents his personal fat bike and plans to add more to a rental fleet this winter.

Gravity Sports in McCall also rents them for $35 for a half-day, $40 for a full-day and $45 for 24 hours. Bikes are available on a first-come, first-served basis.

“We almost always have bikes available for people,” said Michelle Reagan, owner of Gravity Sports.

Jug Mountain Ranch and Gravity Sports hosted the first “Snowy 45” fat bike relay last year and had 44 riders sign up. The race returns March 2, and Reagan said 80 riders have already signed up.

They will also host a fat bike demo day Feb. 15 where you can try a Surly brand fat bike. All the details haven’t been set, so check jugmountainranch.com or the ranch’s Facebook page.

The interest in fat bikes isn’t limited to McCall and other mountain towns.

Jeremy Whitman, manager of Meridian Cycles, has five fat bikes in the shop’s rental/demo fleet, and the shop has sold 25 of them this winter. He sees fat bikes on Foothills trails, and even in downtown Boise.

Idaho Mountain Touring in Boise also rents and sells them, and several bike shops around the Treasure Valley sell them.

The cartoonishly large tires and stocky, rigid frames make them look like throwbacks to the original mountain bikes, and also something entirely different than what people are used to seeing.

“On any given day, I will have five customers come in the shop just to look at a fat bike,” Whitman said.

It’s also not the young, fast and fit looking for a second, third, or even fourth bike. It’s common for middle-aged rider to ride them because they’re stable, simple, durable and fairly low-maintenance bikes.

“They’re kind of built like a tank,” Kathy Muench said.

The bikes were originally built for the Iditabike, an endurance race in Alaska that’s run during winter. Their popularity has exploded in Alaska, according to Dave and Sharon Sell, who split their time between Boise and Anchorage.

Fat bike riders are as common on the trail systems there as Nordic skiers, and the two sports can complement each other because most skiers prefer softer snow, while firmer conditions favor bikes.

“When the skiing is bad, the snow biking is good,” Sharon Sell said.

While the sale of fat bikes has grown in Idaho and beyond, it’s still a niche sport, and people are figuring out new ways to use the bikes.

Like mountain biking 30 years ago, fat bikes — especially riding on snow — is fairly new to Idaho, and it will likely grow and evolve.

“It’s the early stage for us, and the early stage for the sport,” Carey said.

I’m no expert, but I want to pass on some things I learned as a first-time fat bike rider.

• Relax. It’s just a bike, and although it looks big and burly, it feels like a regular bike. It’s not as nimble as your average mountain bike, but there’s nothing about a fat bike that should intimidate you if you know how to ride a bicycle.

• Dress for exertion, so lighter layers than you would normally wear for cold weather, and breathable fabrics so you don’t get damp from sweat. Remember to factor in the wind chill when you’re going downhill. If you start feeling hot, peel a layer, especially before a prolonged climb, then put it back on for the descent.

• For your first time, go with flat pedals and warm shoes or boots. As you become more comfortable on the bike, you might switch to clip-in shoes and pedals.

• Soft or fresh snow is harder to ride than groomed, hard-packed or crusty snow. Fat bikes aren’t powder machines, which is good because there are lots of other fun things to do on fresh snow.

• A higher gear works better to plow through soft snow. You’re more likely to break traction in a lower gear, but you don’t want to burn yourself out in a higher gear. Find a compromise.

• Stay off the front brake on the downhills. Descend slowly until you become comfortable with the traction, or lack thereof. Brake far in advance of corners, steep downhills or obstacles.

• If you’re losing traction while climbing, shift your weight toward the rear tire so it gets better grip.

• Pedal seated rather than trying to stand and grind up a steep section. You will maintain more consistent traction and balance.

• Enjoy the scenery. Fat bikes go slower than your average mountain bike goes on dirt. Pedal, relax and enjoy the fact you’re riding on snow in a beautiful environment.

• Not all groomed cross-country ski trails are open to fat bikes. Jug Mountain Ranch and Tamarack Resort allow them on their trails, but they’re not allowed on the Bear Basin cross-country trails west of McCall, or on the trails at Ponderosa State Park.

• Do not ride on the ski tracks set by the groomer. They are needed for traditional cross-country skiers. Also, yield to skiers like you would hikers.

• You can ride fat bikes on groomed snowmobile trails, but snowmobilers probably won’t expect you out there, so ride with caution. Consider using a headlight and/or red flashing rear light to make yourself more visible, especially on an overcast day.

Remember, parking lots and trail grooming are paid directly by snowmobilers. You’re a guest on their trails.

In this Feb. 6, 2014 photo, fat tire bicycle rider travels the trails at Jug Mountain Ranch near McCall, Idaho. Fat bikes sport oversized balloon tires run at low air pressures that are specially designed to ride on packed snow and other surfaces. (AP Photo/The Idaho Statesman, Roger Phillips)