Winter Is Here: Bring Out The Fat-Bikes!

Winter has arrived, and for many in snowy climates, this means that mountain bikes are hung up in the garage, road bikes are put on trainers, and the countdown to spring begins, waiting for when trails emerge from their blanket of snow, flowers spring up, and another season of long summer days of riding begins.

To pass the dark days of winter, some turn to alternative sports, but a growing number of people are embracing riding in the winter, on the snow, on bikes with 4-inch wide tires.

While snow-bikes, or fat-bikes, aren’t new, a surge in their popularity in recent years has seen the emergence of new frame builders, new wheels, and new tires.

The first mass-produced fat-bike was the Surley Pugsley in 2005. The wide rims and large volume tires were ideal for riding in the Minnesota winters, where Surly is based.

Since then, a variety of companies have built their own fat-bike, including Speedway Cycles’ Fatback, Chain Reaction Cycles’ 9:ZERO:7, Salsa’s Mukluk, and Wildfire Designs’ FatBike.

The number of snow bike events around the States has also increased. While the granddaddy of snow bike racing is still the Iditabike in Alaska, where racers follow the Iditarod trail from Anchorage to McGrath for 350 miles, or even to Nome for 1,000 miles, several smaller race series’ are popping up in snowy states around the country.

The Leadville snow bike series has seen increased participation and snow-biking is also gaining ground in Idaho where Grand Targhee ski resort was the first resort to allow snow-bikes on their Nordic trails.

The concept of a fat-bike is simple: fatter tires provide more floatation on snow, sand, or other soft surfaces, so the entire frame is designed around being able to fit larger rims and tires.

Large volume tires can be run at extremely low pressures, further increasing the floating ability of the bike on soft surfaces as well as increasing traction.

The unique parts of the fat-bike frames are the wider fork and rear triangle, a wider bottom bracket, and wider rims and tires.

Frame and fork

In order to fit 4-inch wide tires, fat-bike forks need to be significantly wider than a standard mountain bike fork. Many fat-bike front forks are built to accommodate a 135-mm front hub, wider than the standard 100-mm front hub.

Some fat bike enthusiasts will put a gear on their front wheel so if something happens to their rear hub, they can swap the front and rear wheel and keep riding.

The rear triangle also has to accommodate the 4-inch wide tire. To do this, the chainstays and seatstays are bowed out and lengthened to the point that some fat bike riders will but a 29-er wheel on a fat bike frame and ride a normal tire in the summer.

When sporting 4-inch tires, a standard bottom bracket won’t allow the chain to clear the tire through a full range of gears, thus most fat bikes have a 100-mm bottom bracket shell and bottom bracket spindles ranging 145-mm to 171-mm.

The geometries of fat bikes are similar to standard mountain bikes in terms of head tube and seat tube angles.

Generally, snow bikers prefer to be more upright than their dirt riding counter parts. Having less weight on hands is a key component to keeping blood circulating in the fingers and keeping hands warm in cold conditions and since snow bikes tend to move at slower speeds, aerodynamics play a less important roll in efficient forward movement.

Wheels and tires

Fat-bike rims come in a range of sizes ranging from 65-mm to 100-mm wide. The wider rims allow the high-volume tires to spread out more increasing the contact area with the snow.

The Surly Large Marge was the original fat bike rim at 65-mm wide but several other companies such as Flattop and Vicious Cycles have entered the fat bike arena with their own rims, many of them wider than the Large Marge.

Surly makes a variety of different fat bike tires for different riding conditions. The sizes range from the Endomorph, which measure in at 3.7-inches wide, to the Big Fat Larry, which comes in at a whopping 4.7-inches wide.

Both the Endomorph and the Big Fat Larry come with a fairly shallow tread pattern ideal for snow and sand, but to complete the collection, Surly has also created other fat tires for people wanting to venture beyond snow and sand on their fat-bikes.

The Black Floyd, at 3.8-inches wide, is a nearly slick tire idea for rallying around on pavement or hard trails while the Nate, also 3.8-inches wide, has, according to Surly, a “shred-your-face-off, run-over-anything, kung fu grip knobby tread pattern.” The Nate can be seen on fat-bikes riding on a wide variety of terrain, including rocky, desert trails.

Optimizing normal bikes for snow

If snow biking sounds like a good time, but the thought of another bike in the garage is prohibitory, most mountain bikes can be made snow worthy.

Rigid forks on hard tails are generally advised as suspension tends to fail at very low temperatures and snow is a smooth enough ride to render suspension useless.

Most modern day frames can accommodate 3-inch tires that will float on firm snow conditions.

The key to being able to ride effectively on snow is to be able to ride low tire pressure. Since there are no sharp rocks to hit on a snow covered road or Nordic trail, pinch flatting is rare, and while tubeless is a viable option for many snow-bike rides, sealant tends to fail at extremely low temperatures, rendering many tubeless systems ineffectual for some locations in the winter.

Like 29’ers a decade ago, fat-bikes are gaining popularity at a rate where mainstream bike manufacturers will eventually have to take notice.

Winter recreational centers will also be forced to consider bikes, so watch for Nordic centers to start catering to fat-bikes in order to increase their user-base. If they build it, riders will come.

Check out more suggestions for how to prepare for winter riding. 

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Eszter Horanyi lives and mountain bikes in Crested Butte, CO.  She has dabbled in road racing, cyclocross racing, and cross country mountain bike racing, but has gravitated towards ultra endurance and multi day self supported racing in the more recent past.  She firmly believes that nothing tops a good ride with good friends on good trails, thus she spends her life in search of all of the above. All articles by Eszter.