They're ungainly and won't win any prizes for speed, but fat bikes are growing in popularity.
With their cartoonishly big tires, they've become a favorite of winter cycling enthusiasts. But as fat bikes proliferate over the frozen landscape, cyclists are running into conflicts with other trail users — especially snowmobilers.
Duluth has an extensive network of single-track mountain biking trails. But during the winter, when there is deep snow, there are few trails for fat bikers to ride.
Because the balloon-like tires of their bikes sink in deep snow, riders need groomed trails.
• Photos: Fat bikers look for a winter trail
Snowmobilers, on the other hand, have developed 21,000 miles of "grants-in-aid trails" across the state. They gain permission from landowners, and pay to groom and maintain them.
The snowmobile trails are illegal for fat bikes, but tempting to their riders.
So before another winter storm blew in Thursday night, Todd McFadden and Chris White got in a fat bike ride along Amity Creek in Duluth.
Their four-inch-wide tires crunched over a packed-down trail that winds through pine trees and crosses stone bridges over the meandering creek.
"We're riding the snowmobile trails because that's all we've got to ride," said McFadden, who bought his first fat bike about six years ago.
Fat bikes are now allowed on some of those trails, but not on grants-in-aid trails like the one they rode Thursday.
"That trail right now, is perfect for riding a fat bike. Our single track trail down here, you can't get on it," he said. "So these few hundred people in town with fat bikes, the weather's nice, good temp, you know where they're going to go."
The attraction snowmobile trails hold for fat bikers is starting to cause problems between them and snowmobilers, said Greg Sorenson, regional director of the Minnesota United Snowmobilers Association.
Sorenson, of Proctor, Minn., said tensions surfaced last week, when several snowmobilers came across a group of fat bike riders.
"They were given the middle finger salute by four of them, and all the snowmobilers were doing were snowmobiling on a trail that's built, maintained and groomed by snowmobilers out of their registration fee," he said.
The solution to such discord, Sorenson said, is to move fat bikes to different trails.
"It's no different than cross country skiers," he said. "They have their own trail system so they're not in conflict with snowmobilers that are traveling much faster."
Most cyclists agree, said Duluth rider Chris White.
"Bikes don't really belong with sleds on the same trails," White said. "Fat bikers are going to have to start to groom their own trails in different places."
To do so, they will have to organize volunteers and pay for trail maintenance, much like snowmobilers.
That's starting to happen. Mountain bikers in the Twin Cities pack down 65 miles of single track trails with groomers they've rigged up behind motorbikes and snowmobiles.
Others are also responding to the growing demand. Giants Ridge Golf and Ski Resort in Biwabik recently became the first ski area in the state to allow fat bikes on groomed cross country ski trails.
John Filander, director of winter recreation for Giants Ridge, said the decision upset some skiers, including his wife.
"She was concerned about the speed, [until] she saw, basically, fat bike speed is about the same as a skate skier on the trail, and if the conditions are such, that the skate surface is firm, fat bikes leave hardly a mark," he said.
Fat bike trails also could provide a potential new revenue stream for such areas, especially during winters with poor snow conditions.
The state Department of Natural Resources has identified some trails where fat bikers can ride, including 10 miles of groomed single track at the Cuyuna County State Recreation area near Brainerd.
But the department is discouraging fat bike use on the roughly 1,000 miles of state motorized trails, like the Munger Trail connecting Duluth and Hinckley. Although fat bikes are allowed there, they create a safety concern, said Pat Arndt, communications and outreach manager for the department's Division of Parks and Trails.
"Snowmobiles have gotten quieter over the years, and if you've got the wind from the wrong direction, and they're going anywhere up to 50 miles per hour on a trail, that is just not necessarily a safe place to be," he said.
Arndt said the agency is trying to figure out where cyclists want to go, and how the state can best accommodate them.
In the 1980s, when mountain biking first became popular, bikers zooming around curves angered hikers and horseback riders. With fat bike popularity now exploding, enthusiasts like Gary Sjoquist, advocacy director for Bloomington-based Quality Bicycle Products, are trying to develop more places to ride to prevent those conflicts.
"How about a pilot program in a state park, where we can build a fat bike trail?" he asked. "Or can we find an instance where we can find a shared use with a groomed Nordic ski trail, so people can see, it's not going to screw up the trail; they really can coexist."
Quality Bicycle Products developed the first fat bike about 10 years ago. Most of the 20,000 fat bikes in existence today are made by the company under its Surly and Salsa brands. With even Walmart selling a $200 fat bike, Sjoquist said it isn't some fad — the fat bike phenomenon is here to stay.