A Fatbike for Every Rider

By Nicholas Carman

 

Touring bicycles, and touring cyclists, have always been an adventurous and capable lot. When balloon-tire mountain bikes first appeared on the market in the early 1980's, many riders quickly imagined new routes and new places to ride. In subsequent decades, the development of 29-inch wheels, suspension, and fatbikes have further influenced touring routes and styles. Based upon unconventionally wide rims and tires, fatbikes are the ultimate adventure bike, suited to the unique challenges of riding on sand, snow, deep gravel, and rough tracks. Many dirt routes are emerging, which empower riders to expand the scope of their travels and spend more time off-pavement. Now, people are riding in unimaginable places with a unique level of creative route-planning. Wanderlust and a fatbike will take them there. 

See a list of fatbike manufacturers here

What is a fatbike tour?

Fatbikers have challenged the concept of what is possible on a bike, and fewer and fewer stones remain unturned each year as new creative routes are explored. These include treks across the snowy state of Alaska in winter; along the length of South America on a variety of ancient stone tracks and unpaved roads; connecting sections of coastline with packrafts and fat tires; and across the Australian Outback along the length of the sandy Canning Stock Route, unsupported. 

However, a fatbike tour need not cross continents, and can be made on a more local scale. Is there an unimproved abandoned railroad corridor in your area, such as the John Wayne Pioneer Trail across the state of Washington? Have you encountered an unrideable sandy track, as on the road out to the Bahia de Sebastian Vizcaino (Vizcaino Bay) to view migrating whales in Baja, Mexico? Do groomed winter snowmachine tracks connect your community to a public cabin, as along the Arrowhead State Trail in northern Minnesota? These routes are prime for fatbike touring, and every state has unique routes that may be best accomplished on big tires. Creative route planning is central to life on a fatbike.  

Fat tire features

Fatbikes provide three features in hearty proportions: traction, suspension, and flotation. Equipped with tires ranging from 3.7-4.8 inches on 50-100 mm-wide rims, fatbikes allow unprecedented amounts of flotation and the capacity to operate at variable pressures. Lower pressures increase the footprint of the tire, providing increased surface area like a snowshoe or backcountry ski. Flotation is essential to the genesis of the entire genre, whose early history is credited to pioneering cyclists in Alaska and New Mexico looking for solutions to ride on sand and snow.  

Traction on fat tires is unmatched. On steep climbs, a tire at lower pressure will deform to make a greater contact patch, forcing more rubber knobs to the ground. 

On rough terrain, a large volume tire provides a basic suspension system, reducing strain on the bike and rider. A pneumatic tire is simpler than a sealed hydraulic system (as on a full suspension mountain bike), which allows more conventional frame designs that are easier to pack for touring.

Riding a fatbike will always draw a lot of attention, as curious onlookers want to know more about “those monster tires!” This can be a good way to meet locals. A fatbike looks like tons of fun, and everyone wants to get involved. Beware if you are afraid of speaking with every single person that sees your bike, as it is inevitable. 

Fatbike challenges

There are a few challenges to touring on a fatbike. As a result of specialty components, including large tires, tubes, and rims, fatbikes tend to be heavier and more expensive than an equivalent mountain or touring bike. Quality fatbikes begin at about $1,500, and base models typically weigh between 33-36 pounds, while premium models weigh less than 30 pounds, and complete custom fatbikes have been built down to 22 pounds. While a superlight carbon fatbike with carbon rims may be appropriate for a short tour with lightweight equipment, a solidly built steel, aluminum, or titanium model may be best when touring with a larger load.

Replacement parts for a few key components are uncommon in most bike shops, including cranks (100 mm BB), rear hubs (170 mm or 190 mm spacing), rims (50-100 mm), and tires (3.7-4.8 inches). This should not be a major concern on short trips close to home, but for extended travel in foreign lands, advance planning may be necessary.

Frame design

Four-inch tires do not fit in a standard mountain bike frame, so some unique solutions are required to accommodate fat tires and a wide range of gears. Early fatbikes, like the Surly Pugsley, utilized a 100 mm bottom bracket borrowed from downhill bikes (68/73 mm is normal), which remains in use today. The Pugsley also uses an asymmetrical frame design, in which a 135 mm rear hub is laced to one side of a rim in a pattern that looks quite strange, but results in a perfectly functional bike and a stout wheel. At the time, wider hubs were not available. The design still benefits riders looking for standard hub dimensions. Offset designs are the easiest way to mate an internal gear hub to a fatbike. 

Recently, most manufacturers have moved to a wide symmetrical rear frame design using 170 mm, and now, 190 mm hubs. The result of each design is similar — big tires and gears are simultaneously possible. The current 190 mm standard builds upon the 170 mm design by allowing the widest rims and tires available, without conflict between the chain and tire in the most extreme gear combinations. It sounds complicated, but fatbike manufacturers have ironed out the details for us so that we can just enjoy the ride.

Fat can be light

As a result of rotund rims and tires, fatbikes can be heavy. As with any touring bike, it is worth considering your individual needs to strike an appropriate balance of strength and weight. A 125-pound rider with a 20-pound load don’t need an overbuilt 45-pound bike with leaden wheels. It is possible to select or design a fatbike that will endure an epic adventure without breaking your back to lift it off the ground. 

Considering the kind of riding that is possible on a fatbike off-pavement and off the beaten path –  pairing a lightweight camping load allows the bike to be ridden to its potential. Panniers do not behave on rough terrain the same way they do on smooth pavement, and are susceptible to bouncing and banging on the rack. Soft luggage from Revelate Designs and other custom bag makers enable rackless touring, and are more than just a solution to save weight. Non-rigid luggage attachments ride quietly on rough terrain, with little risk of broken hardware. The reduced profile of the bike will be easier to thread through tight situations as well.

Wheels and weight

Fatbike wheels compose half the weight of a fatbike. To enhance the riding experience, it is possible to reduce the rotating mass in the wheels without a great loss in strength or durability. Lightweight components have helped to reduce wheel weights dramatically over the last few years. One unique feature now common on many bikes are wide singlewall rims manufactured with weight-saving cutouts. Despite initial trepidation from riders claiming these “holey” rims were only for use on soft surfaces, they have proven durable in many tough situations.  For especially heavy loads, solid rims from the same extrusion are available. Last year, wheels built with solid 82mm Surly Rolling Darryl rims survived a monthlong unsupported trek on the sandy, corrugated Canning Stock Route in Australia. 

Mid-fat concepts

Finally, when flotation is not the ultimate goal but the features of a wide tire is still desired, a new concept exists. A mid-fat tire and rim combination, first available from Surly as a 29 x 3.0-inch tire on a 50mm rim, benefits from improved traction and suspension with a hint of flotation, in contrast to a normal 29-inch mountain bike wheel. Without gaining as much weight as a proper fatbike, and utilizing mostly standard mountain bike components, the “29+” concept may suit some off-pavement tours better than full 4-inch tires. Mid-fat rims and tires are also available for 26-inch wheels, and fit both the Surly 1 x 1 and the Troll. Most fatbikes will accept 29-inch and 29+ wheels, which must be built as a custom wheelset. Dedicated 29+ frames include the Surly Krampus and the touring-oriented ECR.

Now, over a dozen complete fatbikes are offered from a variety of manufacturers. Fatbike equipment is developing at a rapid rate, with a new level of specialization. Whether a fully-loaded trek across uncharted backcountry or a fast and light ramble along sandy river trails close to home, there is a fatbike for every rider.

Bit by Bit

Wheels

Tires are available from a growing list of companies, including Surly, 45NRTH, Vee Rubber, Specialized, Maxxis, and Fatback. Most tires are available in a 27 threads per inch (tpi) wire bead version and a lightweight 120 tpi folding model, the latter benefiting from a more pliable casing for greater comfort and efficiency, and less weight (this is a common feature on road and mountain bike tires as well). While most tires cost between $90-$150, less expensive tires are now available for $45-$60. As a bonus to those on a tight budget, heavier tires with lower tpi tend to be more resistant to sidewall cuts in rough country.

As on a mountain bike, tires come in fast-rolling designs and aggressive, high-traction models. Low profile knobs spaced closely together as on the Surly Knard or 45NRTH Husker Du are best for fast riding in ideal conditions, such as as on hardpack snow or dirt. Aggressive tires like the 4.8-inch Surly Bud and Lou are best for deep snow, mud, beach gravel, and riding on the moon. A growing range of tires exist between these two extremes. 

Rims are essential to a wide tire footprint. Surly produces their ubiquitous fatbike rims in three widths: the 65 mm Marge Lite, the 82 mm Rolling Darryl, and the ultra-wide 100 mm Clownshoe. Wider rims increase the footprint and improve the profile of the tire for increased flotation, although narrower rims will be significantly lighter, and may produce a more responsive tire profile when riding at higher pressures, as on dirt roads and trails. The most common rim today is the 82 mm Surly Rolling Darryl. This dimension provides a useful profile in a range of conditions. Rims as narrow as 45-50 mm may be appropriate for fatbike tires when flotation isn't a priority. 

New rim manufacturers will drive development and lower prices in the future, while the emergence of carbon fiber fatbike rims have enabled even greater reductions in wheel weight. Some ultralight carbon models may be suitable for some touring conditions.

Tubes on stock fatbikes are heavy, nearing a full pound per wheel or more. In situations where punctures are not a common risk, lighter tubes intended for 2.3-3.0-inch downhill tires can be used, saving as much as a .5-pounds per wheel. If punctures are a serious concern, standard size fatbike tubes are best, although DIY tubeless methods are widely publicized on the internet and have proven reliable. Tubeless systems are often lighter than comparable tube and tire combinations, and nearly eliminate the risk of flats. Look for more tubeless-ready fatbike tires and rims in the near future.

Handlebars

Comfort and control are paramount to any touring bike. Part mountain bike and part bushwacking all-terrain vehicle, fatbikes benefit from wide handlebars and a comfortable upright position. These days, many riders prefer upright bars in excess of 680 mm or 700 mm. On rough terrain, titanium and carbon fiber handlebars can help to reduce shock to the hands and arms, although they are more expensive. On longer more casual tours, multi-position handlebars such as the Jones Loop H-bar can help reduce upper body discomfort, available in both aluminum and titanium. Ergonomic handgrips such as those from Ergon are highly recommended on any upright bar.

Gearing

Fatbikes are equipped with a wide range of gears, emphasizing the low range used when climbing or riding through challenging conditions. Most bikes now use a simplified double crankset instead of a triple, with a wide-range mountain cassette in the rear. For a tour in distant lands, a three piece crank that attaches via a square-taper or ISIS spline may make crank replacement easier than with the modern two-piece crank design, in the event of damage from impact. Many quality two piece designs are found on stock bikes, providing a lightweight and efficient pedaling platform.  

Shifters range from push-button trigger shifters, twist shifters, and top-mount thumb shifters as are stock on the Surly Pugsley. Thumb shifters are often preferred by long distance tourists for their simple design and ability to operate in a “friction” mode, especially useful in situations where the system may be compromised by damage or wear. Personal preference reigns, and modern shifters are both effective and robust.

Internal gear hubs (IGH) provide an alternative to derailer systems, sealing the entire gearbox into the rear hub away from the weather and the trail, and removing the risk of clogged or bent derailleurs. Quality IGHs operate in an oil bath with little friction. The 14-speed Rohloff Speedhub is the leading choice for demanding cyclists. Several reputable hubs are also available from Shimano and Nuvinci. All IGHs are designed for 135mm rear frame spacing, found on the offset designs of the Surly Pugsley, Schlick Northpaw, or the 9zero7 Tusken.

Brakes

All fatbikes are equipped with disc brakes. Most bikes use cable-actuated mechanical disc brakes, in contrast to hydraulic brakes which rely upon a closed system of hydraulic fluid and pistons. Mechanical disc brakes such as the venerable Avid BB7 are the most reliable in long-term use, and are much easier to service on the trail. Quality hydraulic brakes tend to be reliable, but when something goes wrong, service is more complicated and small parts are difficult to obtain. For greater stopping power, larger rotors and mechanical disc brakes make a good match on a long tour, although 160mm rotors typically suffice.

Pedals

As always, pedals are a personal preference. Fatbike tours may include some challenging sections of trail, and a good walking shoe may be helpful if forced to walk alongside the bike. A platform pedal also allows easy dabbing of the foot to the ground, which is common on winter trails or on rough tracks. 

Exploring frame materials:

A steel fatbike frame is a good platform for a rough stuff tourer, whether out the back door or across the globe. The Surly Pugsley uses a common 135 mm rear hub and includes attachment points for racks, fenders, and bottles. It is a tough steel frame in a proven design that can be built as a full-loaded tourer with racks, or with lightweight luggage.  

Aluminum frames are known for being light and stiff, as well as corrosion-resistant. The same lightweight frame could be built into an utralight racer or a full-featured tourer. The Salsa Mukluk and the Fatback aluminum frames each feature generous tire clearances, braze-ons for racks both front and rear, and up to five water bottle mounts, making them ideal for touring with or without racks. A lightweight bikepacking load on an aluminum frame could yield a very fun and capable bike, perfect for those moments when the bike must be hauled over downed trees or across a stream.

A titanium frame may be the ultimate touring fatbike. Light in weight, corrosion resistant, and comfortably compliant, titanium frames are available from many companies and custom builders including Salsa, Carver, Lynskey, Twenty2, Muru, Black Sheep, Moots, Erickson, and more.

An ultralight carbon frame may make the difference between riding and pushing in some scenarios. Carbon frames from Borealis and Fatback feature rack attachments points on the frame, although a lightweight frame is best paired with a light load. Superlight carbon wheels are available from several companies; the tubeless-ready doublewall Borealis Carbondale is most promising for lightweight touring applications.

 

Nicholas Carman left on a bike trip in 2008 and never stopped riding. After a full season touring across Europe and the American Southwest, he resides in Alaska for the winter, working towards another round of adventure. He shares words, images, and ideas at gypsybytrade.wordpress.com.


View as PDF