Build-a-Bike: the Fat Edition

In a day and age where consumerism is as much a part of the culture as peanut butter is to a good PB & J, I find solace in knowing that the things that I spend my hard earned money on are quality items that can be 100% personalized to me.

I vehemently detest consumer culture. We as humans are much much more than what we buy (If you haven’t already, please check out the book No Logo, by Naomi Klein, if you want to have your world shaken and redefined on this subject). But for some silly, disassociated reason, I have no problem justifying the purchase of a new bicycle at pretty much any time.

Odds are, I’ll use it.

In the process of building up my own new fatbike, I made some notes should you want some help or guidance in doing the same thing. It’s a lot of work, this whole ‘being picky’ thing. And if this simple guide can make it a little easier for the next picky gal who comes along, than I’m happy to help! Cheers to shredding your dream bike! I hope the following helps you to build yours exactly the way you want to.

— Choosing a Frame —

Welcome to bike buying on planet earth, where an abundance of options will inundate you and leave you feeling numb and opinion-less until you eventually make a decision based solely on someone else’s opinion. Isn’t it the best?

There are so many modern and rad bike geometries on the market these days, and the variety of companies have pushed the standard so high that pretty much anything you desire, you’ll be able to find a top of the line model of. Not without paying a pretty penny, though.

Fatbikes come in the same ol’ varieties of metals: carbon, aluminum, titanium (ti) and steel. The best advice I can give you here is to avoid a heavy metal fatbike at all costs. In a sport where the momentum you’re able to carry directly dictates the amount of fun you’re able to have, you don’t want a ti or steel fatbike. Trust me.

On the fortunate side, fatbiking is totally one of those areas in cycling where I don’t think it matters if you have a carbon or an aluminum frame. In this instance, I would say, go with the less expensive (aluminum) frame and save that money for nicer components. Once you get it rolling, you’ll never be able to tell the difference.

I raced an aluminum frame fatbike my first season and, from my personal experience, your core strength and your power output win fatbike races. The frame material has nearly nothing to do with it. Also, the weight difference between carbon and aluminum fatbike frames is nominal.

My aluminum Specialized Hellga Expert from last year came out to 29 pounds, while many a bike that I sold to carbon die-hards came in at a starting weight of 30 or 31 pounds. The price difference for aluminum and carbon is usually somewhere between $500 and $1,000 between similar builds, money that in my opinion, would be much better spent on a dropper seat post and drive train. But we’ll get to that later.

One thing to be on the lookout for when buying a frame is a threaded bottom bracket (BB). Moisture is nearly unavoidable when fatbiking and the bottom bracket is usually the first place that takes abuse and is usually the last thing to get serviced. Do your future-self a favor and go for the most hardy BB type on the market - threaded. That way, you won’t wind up replacing it a few short seasons after your purchase date.

Corvus FLT Frame:

FatBack, based in Anchorage, Alaska, makes the hardiest and most innovative fat frames on the market. This carbon framed bike is built for bikepacking and racing alike, and comes with a threaded BB, which suited my needs perfectly.

— Rigid vs. Suspension Fork —

The decision on whether to ride a rigid or suspension fork is made simple by determining your application. If you will be riding your fatbike on snow trail only, a rigid fork is all you will need. The bike will handle tightly and responsively and you will never need suspension on the thin white ribbon of pow. Carbon front forks tend to be more flexy than aluminum forks, so keep that in mind when thinking about all of the aggressive cornering you’ll want to do. Ditching that suspension will also make your rig significantly lighter, which is a big plus.

On the other hand, if you intend to use the bike as a trail bike, do yourself and your rims a favor and buy a suspension fork. RockShox makes the fatbike specific Bluto in 80 mm, 100 mm and 120mm variations, while Manitou makes an even lighter suspension fork, the Mastodon, with an even wider range of travel options. Here is an excellent article comparing the two.

RockShox Bluto:

I built up my fatbike with a 100 mm suspension fork and with intentions to bikepack. The Bluto adds nearly 2.5 pounds to the bike - no small amount. But it’s a fair price to pay if you want to enjoy some gnarlier trail on your fatty. Come race season, I’ll switch to the rigid fork which came with my frame and will enjoy the instant weight savings!

— Dropper Seat or Rigid Seat —

To me, this decision is a no-brainer: If you want to have fun on your fatbike, buy a dropper seat post. This is one of the major perks of riding a bicycle in the 21st century - we now get to enjoy a smooth transition between climbing and descending without hopping out the saddle to lower the post.

The dropper seat post has revolutionized the way we ride a bike, and even more so, the way we fatbike. Snow riding can feel clumsy and impossible at first, with your feet sinking into the powder every time you put a foot down. This is frustrating enough, until you try getting on or off of your bike. Without a dropper seat post, this can be an incredibly cumbersome task in the snow. And trust me, you don’t really want to find out the hard way.

Notoriously, hydraulic actuated mechanics misbehave in colder weather. The lower temperature can cause the fluid in the system to thicken, which will have negative effects on the actuation of a dropper seat post and ultimately may cause it not to work. For this reason, I only ride with mechanically actuated seatposts on my fatbike.

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Specialized Command Post:

Dependable performance.

— Cranks & Bottom Brackets —

Finding the right cranks and bottom bracket for your frame is perhaps the most confusing aspect of building a bike yourself. The company that manufactures your frame will have a ‘frame spec’ page listed on their site, associated with your bike specifically. This is like your bikes bible. Read it, know it, maybe even bookmark it, because it can and will come in handy. Here’s why: There are almost infinite different ways to build a bike and it's nearly impossible to order equipment that works for your bike if you don't understand the bikes geometry. This is usually the reason that most people go to a bike shop and buy a pre-assembled bike or talk to a mechanic before they buy components to figure their own build. It’s actually REALLY difficult to know which equipment will work on your specific frame. However, a bike’s frame specs (often listed online as ‘geometry’) is like it’s road map to fun times.

You will want to know the dimensions of your frame’s bottom bracket shell in millimeters. This will help you determine a bottom bracket (BB) to fit. The new standard, if there is one for fatbikes, is a 100 mm shell width.

There are many different types of bottom brackets for fat bikes, but these three are the most common: Threaded (ShredWorthy recommends this kind), press fit ( essentially, a bearing in a plastic cup that fits into the frame, this kind is most commonly stocked), and bb100 ( where a bearing fits directly into a bottom bracket shell, most companies are moving away from this kind).

The SRAM DUB bottom bracket will fit into almost any modern bike. The DUB series provides a standardization for cranksets by fitting into a wide variety of frames, and creating a universal interface for the cranks.

Most fatbikes will work with SRAM’s Fat 4 or Fat 5 series of cranks. The only difference between the two, as it turns out, is the chainring offset. The Fat 4 comes with a 3mm offset while the Fat 5 comes with a -4 mm offset. The standard crank length is 175 mm, while a lot of small or extra small frames are spec’d with 170 mm cranks.

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SRAM DUB & GX Eagle Cranks:

I went for the new SRAM DUB BB because I think industry standardization for bottom brackets is one of the best things to happen to the cycling industry in a long time. The 175 mm GX cranks were an easy and inexpensive option for me on this build.

— Drivetrain Options: 1x vs. 2x —

What is the difference in a 1x (one-by) and 2x (two-by) system?

Maybe you’ve heard about the craze sweeping bikes into a new era of modern. Maybe you’re a skeptic who has never tried 1x, or sees no reason to.

Well, pretty much every 2017 or newer bike that you’ll see sold in a shop has a single front chain ring and no front derailleur. This is a 1x.

‘How can they take away a feature on a bike and call it better?’

I’m glad you asked.

A 1x system not only removes the front derailleur and limits you to a single front chain ring, but it also removes the left-handed shifter on your handlebars since, in this system, there is no front derailleur to shift. This makes the bike more simple, which makes it more fun. You’ll no longer find yourself on trail wondering if you’re in the right gear. With a 1x system, you shift based on what feels right, only using the right hand. This allows your focus to stay more tuned in on trail.

An added benefit of this lack of a second shifter is that it clears up some space on your handlebars. Not only does this look cleaner, but it allows for more features, like a dropper seatpost lever. If you plan on getting into bikepacking, this also frees up room for bag attachments on the handlebars.

Almost always, I will try to steer someone buying a new bike towards a 1x drivetrain. Unless you are specifically looking for antiquity, 1x drivetrains are simply more streamline, they are current, and the benefits outweigh the downsides in my opinion.

However, many riders fear transitioning from a 2x to a 1x because they are concerned they will lose too much range (how hard or easy it is to pedal). Sometimes this is the case, but not always. In a 2x system, there is usually a pretty large number of overlap in your gearing (some combinations end up requiring the same amount of force required to pedal). The 1x system eliminates the overlap and potentially also eliminates some of your high end gearing (which would only ever be used when downhilling a bike at roughly 30 plus mph). The average rider has no need to go 30 mph on a bike, and thus the 1x system is a practical and simplified way to ride.

With the 1x system as the new standard, 11 speed and 12 speed cassettes rule the market now-a-days and for mountain biking, SRAM offers the best drivetrain in the game: the eagle 12 speed drivetrain.

While you can’t get one of these drivetrains without selling an arm and a leg, I can just about guarantee you that you will have worlds of fun riding a 12 speed, and that as far as bicycle components go, wide-range drivetrains are probably the best bang for your buck.

What this wider sprocket in the rear does is offer you more low gears, or climbing gears. These bigger gears in the back require less torque and less energy expended to go up a hill. ‘Well why would I want that?’ you might say, ‘That will only make me slower.’

While in theory, that is true, in practice, it’s not the case. Having a wider gear range, and accordingly, more low gears, means that you’re saving energy when you need it most and not blowing up your legs on the steep climbs.

This past winter, during the 28 Below fatbike race, Michelle and I were riding neck and neck, trading the first place women’s position back and forth. When we came upon the last climb, a steep quarter-mile pitch to the highest elevation point on the course, Michelle maintained her speed, holding a fast cadence while I had to hop off my bike and hike my way up, falling further and further behind her. What played a huge role here was our gearing differences. Michelle was riding a 12 speed cassette while I was riding an 11 speed. I didn’t have the low end (easier) gears that she had to pedal up the mountain. In retrospect, it would have made more sense for me to have been running a 12 speed drivetrain, since I had bumped up my front chainring to a 32 tooth.

12 speeds give you the advantage of bumping up to a bigger front chainring and still winding up with more low end gearing than if you were to stick with an 11 speed.

Playing around with gearing can be a fun, but expensive process. I ended up finding my sweet spot last year on a SRAM 11-speed XO cassette with a Wolf Tooth 32 tooth oval front chainring.

It’s worth noting that if you plan to bikepack on a weighted bike, a smaller front chainring may be the way to go. Since climbing with extra weight is made more difficult, it is wise to gear your bike towards climbing rather than speed for these sorts of long distance endeavors. A common bikepacking drivetrain combination would be a 28 tooth front chainring and a 12 speed cassette.

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SRAM X0 1 x 11 Drivetrain:

I have run into a little bit of difficulty finding the drivetrain set up that I want for this new bike. Because no one seems to manufacture a 32 tooth chainring with a -4 mm offset, I have maintained my 11 speed drivetrain rather than converting to 12. This will have to do for now.

— Brakes —

Hydraulic lines, as I mentioned before, historically react badly to cold weather. This is a strong argument for mechanical brakes on a fatbike, in my opinion. However, I have never ridden mechanical brakes in the snow, nor would I want to (since my goal in the snow is usually to go as fast as I possibly can, including stopping as fast as I possibly can). I have never had a problem with my hydraulic Guide brake lines “freezing up”, and for that reason, I will recommend the 4-piston SRAM brakes that bring me to a halt quickly and consistently whenever I ask them to.

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SRAM Guide Ultimate:

These 4 piston brakes offer serious and reliable stopping power, which is essential to good fatbiking.

— Hubs and Rims —

Your rim choices abound for fatbikes. Much like choosing the fork for your bike, your rim choice should really depend on your planned application. Will you be racing this bike? Choose carbon hoops. Will you be riding this bike year round? You might want a slightly more narrow rim, like the SUNringlé Düroc (think 50 mm as opposed to 80 mm). If you plan to ride groomed snow exclusively, you can go with something much lighter and less beefy, like H.E.D.’s BAD rims. My fatbike has two planned applications: a bikepacking rig & a snow race machine, so accordingly, I have purchased two different sets of rims: an aluminum narrow pair for trail riding and bikepacking and a carbon 80 mm set intended for snow use only.

The rolling mass of your fatbike is a very important aspect. I would recommend spending a little bit more money here, so that you can optimize your fun to dollar spent ratio. The lighter your wheels are, the more momentum you will be able to carry in the snow. Keep this in mind while you’re shopping.

There are currently two different common rim diameters for fatbiking: 26 and 27.5. 26 inch wheels are definitely the industry standard but the 27.5s offer a little bit more traction by providing a bigger contact patch at any given time. If given the option, I recommend 27.5 wheels for fatbiking, as more traction is always a huge advantage in the sport.

As far as hubs go, DT Swiss makes an awesome set of fat hubs called the Big Ride 350s. These ratcheting hubs are great for riders who can lay down the power, and are easily rebuilt, should they get used and abused like any good fatbike should. However, the top of the line hubs always come from Industry 9, and if you have the extra money to spend, Industry 9 is known for building hubs that can withstand terrible weather conditions and they require the least amount of servicing out of all the brands on the market. Plus, they offer the rainbow of colors in hub options. So, you could customize your bike even further, while adding significant quality where it matters most: in your rotational mass.

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DT Swiss Big Ride 350

I went with these hubs because they are reliable, competitively priced and easy to rebuild if need be.

— Finally, Tires —

This is often an after thought when building a bike, but for fatbiking, this is an exceptionally important aspect. Keeping your rolling mass as light as possible without sacrificing traction and big lugs is a tough game to play.

I started off my build with Maxxis FBF tires because they were the only 27.5 fat tires I could find. But I quickly learned that while the traction provided by these big lugged tires was great, the extra weight wasn’t worth the benefit and made the bike feel sluggish. That’s not a good feeling.

I switched to the 45NRTH VanHellga and have been loving the feel of the bike since. These tires are the perfect mix of heavy duty and light weight.