Fat Bikes: An Explanation For The Curious

 The other day in the comments section I got a question about fat bikes in general which prompted me to publish this post. The question I got was prompted when a reader of the blog noted that I made distinctions between capabilities of my three fat bikes. This was something I discovered some time ago, and realizing that not all fat bikes are created equal was why I commented as such in the post. The question then, distilled down to its elemental basics, was , "What are the characteristics and differences between various fat bikes?"

I will attempt to answer this question based upon my experiences over the past nearly 10 years of riding these things. Plus, I have a reference series I wrote in 2016 on this very subject which I will link to at the end. So, here goes......

The Snow Dog during a ride back in January of 2011.

The earliest complete fat bikes which were available were based upon what had come before which was an evolution from 26" mountain bikes of the 1990's. The geometry of those days informed the earliest forms of fat bikes and the Surly Pugsley of 2005 was pretty much following in the footsteps of those early pioneering efforts. The main focus of design was endurance and expedition. The bikes then reflected these traits. Racing (in the XC MTB sense anyway), mountain biking, and other uses of fat bikes weren't ever a consideration then.

The primary limiting forces on design in those days were tires, rims, and the perceived need to accommodate triple crank drive train capability to preserve a wide range of gearing. Since these driving forces were what informed the complete fat bikes that appeared out of Salsa Cycles in 2011, the same that had also influenced the Pugsley, it meant that we had inherited the same limitations on tire/rim sizes and in regard to what was thought in terms of drive train needs. 

For instance, the Mukluk which debuted late in 2010 had a triple ring crank, front derailleur, of course, and a fairly limited rear tire clearance. Not that you could get a tire to fit to max out clearances, because the new Larry tire was only a 3.8" wide tire. (Most probably the Big Fat Larry was already on the drawing board by this time, which would max out tire clearances on the OG Mukluk) So, why weren't these bikes future-proofed? Surely by 2010 it was becoming a thing for mountain bikes to have 2X drive trains, for instance, which would have allowed for even wider tires in the future. Right? 

Well, of course it was, but what wasn't anticipated was that fat bike demand would be so ravenous that bikes couldn't be made fast enough to satisfied demand. Now this necessitates a look at the business side of things circa 2010/2011. This period of time was when the whole 29"er craze had all come to a head and those crazy days of increasing sales from 2007-2009-ish were slowing down. The economic downturn of 2008 had affected the economy as well, so bicycle dealers and brands were looking for the "next big thing". The 650B based, long travel mountain bike scene, (yet to be dubbed "Enduro®") was just getting going, and that was one band wagon brands were jumping ship to for sure, but this Winter-time craze of riding corpulent sized tires in snow was something entirely new. Salsa and Surly dealers, who normally would have been shedding dollars in the off-season, now had a product that was flying out the doors. And this did not go unnoticed.....

One of two prototype test bikes Salsa Cycles had made to develop the Mukluk. Seen here at Interbike 2011.

Remember, manufacturers and brands were looking for the next trend and were not about to be left behind as many were when 29"ers took off. So, seeing the success of Salsa Cycles and Surly, the R&D to bring new fat bikes to market leapt into action. By 2012 there were so many more fat bikes out, or coming soon, that you could not keep track of it all. This in turn pushed innovators to dream 'bigger', and the fat bike pioneers, mainly Alaskan brands like Fat Back and 9-Zero-7, saw a way to keep one step ahead of things and pushed the 150mm front/197mm rear standard. This allowed for 100mm rims and the widest tires, (at the time 4.7" wide) and still have plenty of clearance. The single front chain ring pretty quickly took over as well as this eliminated the complexity, weight, and snow/mud clogging of front derailleurs and shifters. Limitations that Salsa and Surly accepted due to what was available and due to perceived demand previous to 2011 were now being swept aside.

Flotation was the name of the game, and if you wanted to traverse the deepest snow, cruise marshy, wet lands, or go where there was no single track at all, but just deer trails or the natural forest/wood floors, these big, fat tired monstrosities were the thing. But not everyone wanted or needed that. Fat bikes soon also became mountain bikes, bike packing bikes, and even full suspension and racing bikes. Heck, people were using them at gravel road events and fat bike categories soon popped up at many gravel events. 

So, now days you have to figure out what it is that you want from your fat bike. Expedition? Cargo? Racing? Cruising trails? A way to get outside and stay fit in Winter? There are a bunch of ways to tackle any of these desires. To that end, I wrote a four part series in 2016 to help you choose a fat bike that is right for you. Much of what I wrote then is still true today with the possible exception of full-suspension fat bikes, which have tailed off in availability in the last few years. (Used examples are still coming up for sale all the time though) Also, the Cargo/Bikepacking fat bikes, like Surly's Big Fat Dummy or Salsa Cycles current Blackborow are not covered as they didn't exist yet. So, here's the series if you want to check it out:

How To Choose Your First Fat Bike: Introduction

How To Choose Your First Fat Bike: What To Look For

How To Choose Your First Fat Bike: Types Of Fat Bikes

How To Choose Your First Fat Bike: Or Something Else!

The cargo category of fat bike started with Surly's Big Fat Dummy

Since I didn't cover cargo fat bikes in my original series, I will say a word or two here. First of all, these rigs are huge. You need to consider storage space, transporting such rigs, and whether or not you'll really need one. The Salsa Blackborow is a bit more manageable in these regards, but it still is a longtail bike. These aren't necessarily your first fat bike, but for the right conditions and for the right person, this type of rig could prove invaluable.

Then as I re-read the series I noted that I mentioned a few things about tires and wheels, which I never really detailed. So, following are some differences with regard to wheels, rim widths, tires, and a word about axle standards.

Some fat bike tires, like this Terrene Wazia, are stud-able.

Wheels for fat bikes are defined by diameter and the width of the rim. A more trail worthy, more XC MTB type fat bike would have a narrower rim. 70mm-80mm would be in that category. Expedition type fat bikes which require more flotation would have wheels with wider rims to help spread out tires and give better stability at super low pressures. 90mm-100mm rims are in that category. There is some cross-over with some folks using 80mm rims for their lighter weight as expedition category rims, but wider is typically better for flotation. Go narrower for more of a MTB experience. 

Diameter can be either 26" or 27.5". The 27.5" size is a newer standard and it is said that you don't need quite as wide a tire or rim to get similar flotation results as you can with the wider 26" based stuff. I've never tried the 27.5" stuff, so take that with a grain of salt. 

Tires can be 3.8-4.2" which would be best with older fat bikes, fat bikes used for MTB, or gravel riding. 4.5"-5+ inch tires are getting into that max flotation, expedition, go anywhere category. Studded tires exist, but are really expensive. I'm not a huge fan of studded tires, but some people cannot live without them. You have to decide for yourself there. Don't ask me because I'll probably never do a studded fat bike tire. It's just not my jam. Prices for fat bike tires are anywhere from a little under 100 bucks to close to 200 bucks a pop. Expect to spend more like 200-250 for a single studded fat bike tire that is worth its salt. 

Axle widths are almost always the 197R/150FRT standard now, but 150frt/177 rear is also somewhat of a thing yet. Older bikes are quick release, may have weird brake standards, and vary in axle standards quite a bit from modern bikes, so beware in the used market should you decide to go that way. You may get stuck with an outdated fat bike wheel set standard.

And with that I will end this rambling post. If you all have comments or further questions, I'd be glad to entertain those in the comments section. Thanks for reading!