SPOTLIGHT: Fat Bikes – Are they here to stay?

Contributor: Den Koh

Additional stuff: Bikezilla




"A fat bike is characterized with humongous tires which necessitate the use of a longer than usual bottom bracket spindle in order to have a workable chain line. These are the 2 physical characteristics which set them apart from other bikes."


You seen them in magazines, you seen them in videos, you used to only see them at the beach. But now you see many more of them in trails – "floating" above the muddy patches and bashing down rock gardens just like any other trailbikes. Even at many jamborees, you can find riders covering an average of 50 km at one go with them! Enter the Fat Bikes! Just what is so interesting about the fat bike? Stability? Novelty? We hear the common "defense" from fat bike riders that they only wanted a fun ride, and being the fastest or plushest is not on their agenda. Just what does that mean anyway? To really understand what draws seasoned riders towards fat bikes, it is best to hear the opinion from a fatbike rider. Bikezilla spoke to Den Koh, long-time avid fat bike rider who gave us the lowdown on this unique bike genre.




Den Koh shares his Fat Bike Experience


Hair splitting of genres in the mountain bike world has everyone going into paralysis mode over their analysis of bike choices these days. Out comes the fat bike tsunami and there’s no mistaking the glaring space this category of bikes has separated itself from the rest. 

Often greeted with mixed feeling, especially from seeing the comical behemoth hoops and rubbers for the first time but the “Way of the Fat” have paved the path with its ever growing rumble. Respectable biking publications have ceded generous portion to blotting up on the virtues of expanding girth.

Not a single ride goes by without someone asking me “Is this (my fatbike) heavy?” or “Can this bike climb?” My best answer has always been a smile and following close behind while waiting for an overtaking opening on some steep technical sections. Show of prowess? Nah. More to follow on the pros and cons later. 

Due to the versatility and fun factor offered on such bikes which already has a rather dedicated following before the explosion of all things fat in biking, it’s a likely segment of the bike industry to stay and not fizzle where some have been down the road. 

Continual support and development within the industry is crucial which in turn depends on market demand. From the way things are steamrolling along with something “fat” being showcased faster than the reproduction rate of rabbits, I’m willing to hedge a coin to say they are staying for sure.



What’s a Fat Bike?

While fat bikes started as things ridden in snow, by now, ranging from trail duties to cruising miles of sandy beach it has become an almost “do-it-all” type of rig. Trying to pigeon-hole it into a specific category gets more complicated by the day with all the added developments of the last two years.

With the recent launch of the Rock Shox Bluto, fat bike is in the lime light yet again. If that is not enough, the two year prototype testing and unveiling of Salsa’s first to be mass produced full suspension fatbike, Bucksaw, is having eagerly awaiting fat bikers delirious with the news of its coming launch this autumn.

Finally fat bikes are joining the ranks of suspensions as in all other categories of mountain biking. Apart from the constraints of jamming all the suspension in there with the girth of the tire needing extra wide crowns and certainly very different damping characteristics, suspension has always been met with a certain amount of disdain by the fat bike purists. There’s no shortage of purist in other riding discipline but in the fat biking world they do make up a larger proportion than most other biking categories.

Keeping it short, in essence, a fat bike is characterized with humongous tires which necessitate the use of a longer than usual bottom bracket spindle (usually a 100mm) in order to have a workable chain line. These are the 2 physical characteristics which set them apart from other bikes. 

As to the mind boggling array of hub standards coming out faster than drive train can catch up to, again it’s all for catering to ever widening need for a chain line to clear all the cogs to the chain rings. 

So how fat before its considered fat? No hard and fast rule really.  Due to the legacy of the Surly Pugsley (the first mass produced fat bike but certainly not the first) with those 65mm Large Marge rims and 3.8 Endormorph tires, that pretty much sets a benchmark of sort that most go by these days. 

Again with all the developments, lines have been blurred further. Some would argue, 47mm rims mounted with 3.8” rubbers or even just 3.0” – 3.5”looks pretty fat too. Actually that’s just how things were in the very early days with the 44mm Snowcat rims. 

I just go by good old eyeball-O-meter these days. If it whizzes by and looks blubbery odd, chances are, you’re looking at a fatbike or one of the many variation out there.


History of Fat Bike

Sure the Pugsley was the one that got the ball rolling when it first debut and gotten everyone gasping and ogling but folks have been experimenting with various things from long before.

Suffice to say production fat wide rims are a pretty recent phenomenon, like early klunking days of mounti bikes, fat bikes started out when someone had an idea to weld and pin normal rims together creating a wider profile to ride around in the snow. (And so we all read this somewhere before)



Characteristics and Applications

My utmost respect always goes to good trials-turn-trail riders. Give them just about any bike and they can ride in just about anything.  As for the rest of us which probably comprise 99% of the biking population… we have come to rely on the differences in various categories of bikes to do our bidding.

More often than not, fat bikes make things a lot easier apart from their intended purposes of trashing in snow, mud and sand. Bring it out on the next ride with the lycra clad 29er XC boys and it fits right at home with that wheel size cluster. Riding pretty much the same but with added stability. Turn around and join the next group of 6” travel trail ride group and it wouldn’t miss a beat.

An argument has always been that it takes more at startup to crank it up to pace which makes it “slow”. Truth is, any biker worth their salt with even just moderate riding experience under their belt would not be all that bothered. 

Neither would the majority of us be pedaling 45km/h on the straights even with an XC bike and keeping that kind of speed and momentum for the entire duration of a ride. Once up to speed, momentum does help fat bikes roll along quite smoothly. Like all wheeled creations, factors like tire tread pattern and air pressure applies – resulting in varying rolling resistance versus traction. 

If you are fat biking, chances are you would be looking for a different fun factors and a little additional rolling resistance is not really a concern. 

Unlike the days of the Pugsley when tire was generally one size – the 3.8” Endomorph, the current market is offering more tyre widths with more features.

One of the biggest hang ups people have when buying a fat bike is how big a tyre can the frame fit. As mentioned, with fat bike trend progressing so fast, being “Bigger, Wider, Fatter” is like a typical fat bike shopper's check list. It might be a case where a frame has just been launched and already their 4.0” clearance with a 60-70mm wide rim is considered outdated. Many fat bikers are constantly trying to fit their frames with fatter tyres. they may not be successful sometimes as the wider wheels may affect chain lines.  One way to mitigate would be the use of 1x drivetrains in line with the industry trends of today. Hence it is important to know your fat bike well before up-sizing it so as to maintain “smooth operation”.






Hubs and Offset

From the early DIY days of hacking and slapping things up, it took a while until the 65mm rims and 3.8” Endomorph combo of the Pugsley that roamed the world for a good period of time came along.  Right up till quite recently the appearance of the first 100mm rims, the Clown Shoe, from Surly. All these were still on traditional 135mm rear hub laced with what many consider insane amount of offset, 17mm and 28mm respectively for the 65mm and 82-100mm rims used on those frames. 

Like the Cambrian Explosion in Evolution, all things fat-bike related had taken off and flourished after years of being stymied, relying on a few small companies to push on and the gatherings of fat-cionados all over the world waiting with fervor for the announcement of items on their fat-bike wish list being fulfilled. 

Many have asked why the peculiar offset frames and offset lacings. Those were necessary before the advent of longer hubs to accommodate the chain line clearance. In the world of fat biking—riders are obsessed with the notion of “float” hence we the growing footprint of these tyres. The last statement would probably bring on the ire of the snow terrain riders considering the "float" theory was originally derived for bikes that can ride in the snow. Truth is, even for the Asian mud riders, the “float” factor on how the tires can easily skim the nastiest mucky goo is why fat biking has a place ib Asian terrains.

When rims started going wider into the 80mm and eventually 100mm territory, the hubs followed with increasing length as manufacturers started to experiment with various geometry changes to the frames concurrently. From 135mm things evolved to 170mm in the rear and now some brands are pushing their 190mm.  What’s next? 210mm? Who knows? The long vs the short of hubs like so many other bike topics are incessantly discussed, argued and likely to continue till end of times.

Front has gone with a 135mm for quite a while but the latest RockSHox suspension fork, Bluto, has gone with yet another.  A 150mm wide front hub. Before lambasting on why “yet another new standard”, it’s been shown that with this width and an accompanying wide crown up top, the fork is able to clear the mega combo of a 100mm rim x the biggest 4.8” tire out there. Before this, other fat bike suspension forks are meant to clear 65mm rims running 4.0” tires, although many have pushed the limits with up to 82mm rims.

Due to the various chain line constraints, the 1x drivetrains has been gaining favor. Using 1 x 10s and 11s drivetrains would make a lot of sense especially for those running mega tooth 40-42t rears to keep things light and chain lines happy.

In all honesty, with the added weight, traction and all on a fat bike, even the strongest riders on the trails are spinning on granny gears. Only ego would keep one constantly on a 32-36 front chain ring at 5-6 psi chugging roots and rocks.


Tyre Pressure

The whole “float” discussion goes hand-in-hand with low tyre pressure. While typical trail bikes use lower than road bike tyre pressure so that the tyres can deform to accomodate the undulating terrains in the trail, fat bike goes one up in using single digit tyre pessure (psi) to leverge on the tyres' deforming, bouncing and wide contact area for floatation and stability.

In short, the want for flotation (that is having the bike gliding across otherwise tyre sucking mud or soft  fluffy snow or slipery sand dunes) had riders tinker with tyre wishlist and that in itself is a key driving force for the fat bike evolution. (Think economic terms: Demand and Supply). More choices became available, in terms of tread patterns, tyre widths and rubber compounds.


Wheel Weight

All cyclist thik about weight weenying to a certain extend. But to a fat bike rider, rotational weight weenying is a holy mission. From the mind boggling array of carbon rims and lightweight tyres available these days there are loads of options to choose from. Weight weenying also comes with a good incentive to improve aesthetics of the bike. But it doesn't come cheap.



Pros and Cons of riding Fat Bikes in Tropical Terrain


With no snow or sand dunes, essentially it’s down to chomping down jungle trails caked with mud in the wet Monsoon months when it comes to fat bike riding in South East Asia.  Fat bikes have certainly proven their versatility taking in the worst that the goo has to offer in the rainy seasons. 

Riding a fat bike in muddy and rainy conditions has an edge over the typical trail bikes in that, it just seem more fun and easier to tackle those goo and mucks. Of course, that is provided a rider has that many bikes to choose from.

What fat bikes lack in the department of being lithe and lightning quick, they easily makes up in terms of stability. They make surprising quick work going up those short technical sections that abounds in our local roller-coaster style terrain whether it’s wet or dry. Where normal size tyres struggle to find a line to punch through or the much desired grip on a wet day, a fat bike can easily take a “dirty line” that would be considered difficult or impossible with say even 2.5” All Mountain tyres. Often in those scenarios, trying to do the “impossible” could mean risking a front wash-out. But, not necessry so with a fat bike!

Can it get any better? Fat bikes are not race bikes. With this in mind, exploratory rides are where big wide wheels can really be appreciated. Fat bikes seem to give riders the feeling that they are monster trucks in a world full of trail bikes, which now look like the typical 4x4s.

On the other hand, owing to the geometry and characteristics that gives the kind of advantage over skinnier brethrens, the steering and handling are rather different. Swift railing over berms requires some getting use to as opposed to what is normally done with relative ease on typical trail bikes. 

Riding a fat bike also requires certain re-learning on where to put one’s center of gravity and making subtle shifts to body weight which is important for smooth and flowy rides. It is like, things just went back to basic. Remember the days before suspension eat up every bumps for you? The rigid mountain biking days where limbs are one’s best suspensions? Even with the low tyre pressure and fat bouncy tyres, the rider will still has to adapt to the characteristic of how a fat bike behaves in different situations.

With low running tyre pressure and the wide contact surface with the ground, many experienced what is termed “self-steer”, where the bike seems to have a mind of its own and go in a certain direction, having the rider to expend a little more effort in keeping a straight line. That being said it usually boils down to finding that sweet spot for the bikes' tyre pressure rather than something being inherently wrong with fat bikes with regard to this self-steer phenomenon.

When cornering, fat bikes with its current typical geometry may give a feeling of under-steering feel that requires some pre-emptive anticipation. Many factors could have caused this, and it may differ from bike to bike depending on each bike's set-up.


What’s Next for Fat Bike?


Suspension is definitely the in thing now. Purists turns a nose up at the mention but let’s face it, with the way fat biking movement storming the scene and making their presence into just about everywhere, it’s only a matter of time when more folks will be trying to push the limits and ride it into harder and more gnarly terrain. Fat or not, screaming like a banshee down a kilometer long rock strewn trail, suspension would be the foremost yearning on anyone’s mind with all the jarring and arm pump fatigue setting in.

With all the mainstream brands already in the game by now, what’s next? Cheaper bikes and knock offs are certain to follow. While there are truly budget conscious and decently specced bikes like the On One Fattie, I’m beginning to see many SGD$1500-2000 fat bikes being sold with components that don’t really make the grade for trail use. Just a personal opinion, fat biking can demand quite a lot from the drive train with the kind of constant high load torque delivered. Buying one of these cheaper rigs and followed by the essential upgrades may not be all that cheap as compared to starting off from a better specced bike from a better known brand. 

A sub genre that would catch on would be electric fat-bikes or add-ons to make them work as such.

Lighter rims and lighter tyres as of any other types of bike. And also, with improve in carbon fibre manufacturing techniques and chances of lighter and stronger metals, bikes will only get lighter from here. But it would reach a point of diminishing return when things become overly light at the expense of strength and durability. It has reach a point by now where 80mm rims are at a sub 700g range.

Lighter tires will come at the expense of 2 things. Firstly, if aggressive knobs are not needed, less rubber on the tyre translates to a lighter tyre. Next would be the sidewall. It’s a moot point to argue that just because some specification like tpi (thread per inch) count is high and the weight is light the tire would still be strong. When push comes to shove and your hoops are getting gutted over rocks, that’s where the test of strength in a tire comes in. Simply put, lighter tires are simply thinner and weaker tires. Choose one according to how you ride and carry tire patch (not just tubing patch). It has come in handy a couple of times for me when I was over zealous at some rocky sections that chewed up the sidewall into tears.


What to Look Out For When Shopping for a Fat Bike


Shopping for a fat bike these days isn’t the easiest thing with all the choices and consideration for whether its future proofed? Evolving standards which do not seem to be slowing down anytime soon is adding to the complexity of making a decision.

For many here, a fat bike will not be the first nor only bike. Most are curious on what these are all about. Basic question to ask is what the fat bike you intend to purchase will mainly be for.

Fat bikes are versatile, it can be changed to a number of different configurations like touring or simply leisurely commuting around.  But if like most, you are going to use it as “another mountain bike”, then of course you would want the same kind of components that can withstand the abuse of off-road riding rigor and with fatbike, maybe a little tougher and better as it can be hard especially on drivetrain components. All those dirty impossible lines that you can take and smile at Mr 2.1” XC does take a toll especially if you are an all-out hard riding type after awhile.

Next, are you in “the bigger, the better” camp? Check out manufacturer’s specification on what they say about the biggest combination of rim width and tire size that their frame can take. Not all fat bikes are created equal. In general if you have something that will clear the biggest and decide later on that it is too much wheels or simply want something smaller and more nimble, there are options to downsize. Not the other way around.

IGH or Internally Geared Hub is popular for the derailleur-haters out there. But if that is one of your consideration, take note that up till now there seem to be no makers for anything bigger than 135mm. This pretty much reduces the choice of frames to those with offsets like Surly or the Muru Finke. Couple of other brands like Salsa and Fatback offer adapters on their 170mm frames that can take a 135mm IGH.

Drivetrain considerations for custom build fat-bikes.. As most brands are banking on 1x drivetrains and the more expensive models running 11s components it would take a little research if you are still relying on cheaper 2×9 or 2×10 options to custom build after buying a frame. For some, like the Moonlander, things like a problems solver adapter for the front derailleur would be needed when running a 2 x 9 or 10 without running into quirky chain line issues would mean using a crank that is specially designed for this particular frame, the Surly OD crank.

Tires are not a cheap thing on fat bikes compared to normal mountain bikes. Each piece of these rubbery walrus carcass can easily run 2-3 times more than an average mtb tire. So do factor into the cost when buying a whole bike to see that what is spec is good enough to take some abuse on the trail. 



Bikezilla Conclusion (For Now …)


The reason fat bikes seem to be associated closely with the "fun" theme could be due to the fact that there are more lifestyle flavour associated with this genre as compared to the other types of mountain bikes. At the same time, fat bikes naturally exude a masculine feel regardless of where it is ridden. This makes fat bike a contender for a "fun" (yes it's that word again) bike that may serve as a do-it-all for some and a leisure city bike for others. On the technology development front, while much researches had been done for all the other types of mountain bikes, things are  just heating up for fat bikes. With the anticipated increase in demand for fat bikes, we see a lot of possibilities for fat bikes, maybe even a genre that has many sub-genres in time to come. Let's see if what we think becomes  reality.


We would like to thank contributer Dan Koh for sharing his views and exprience on this topic. We woud also like to hear the views of other fat bike riders on the issues discussed. We would suggest using the Bikezilla forum page to discuss on this topic further.



Photos used with permission from Den Koh, Sammy Tan and Halil Hassan