"Why?" is the wrong question. Fat bikes are all about "Why not?"
Fat bikes are those cartoon-looking mountain bikes with huge tractor type balloon tyres. If you fancy one, here’s what you need to know.
The general tyre width window on fat bikes is 4in to 5in. Typically and historically speaking, the rim size is usually 26in. But there are now 27.5in rim fat bikes coming out. And, as ever with fat bikes, there are folk who have gone OTT and made 29in fat bikes.
It’s arguably best to ignore rim size for now. Tyre width is far more important with fat bikes.
Anything narrower than 4in and you’re dealing with a Plus bike, or even the just-don’t-call-it-Plus range of mountain bikes that come with 2.6in tyres now.
What are fat bikes for?
That’s a surprisingly difficult question to answer. Although it is true that fat bikes were originally invented for riding across sand or snow, that isn’t the reason why fat bikes exist now. The vast majority of fat bikes are ridden on the normal trails that you ride any mountain bike on.
You can ride fat bike… anywhere. Fat bikes are first and foremost about grip. Traction tractors. The fat tyres aren’t really a substitute for, or alternative to, suspension. Don’t go for a fat bike if you’re looking for a suspension bike experience. Fat bikes aren’t best treated as bump soakers. They’re for hoovering up terrain. ‘Floatation’ is a commonly bandied about term.
Why ride a fat bike?
There is one simple answer. An answer that trumps all other answers: because you want to. You don’t have to justify it.
That said, the market for fat bikes is far from straightforward or free of tech. Once you go down the rabbit hole of fat bikes you’re quickly into the complicated compatibility-strewn world of Q-factors, hub widths, chainlines and super-precise PSI.
How floaty do you want your fat bike to ride? The principle choice here is 4in tyres or bigger-than-4in tyres. Not many riders are well served by tyres bigger than 4in.
Unless you genuinely are mainly riding on sand or snow, don’t get instantly sucked into the temptation of the fattest tyres possible. They’ll be insanely sluggish and bouncy and will quickly become not-fun. And fun is what this is all about.
4in tyre fat bikes offer the complete fat experience with hardly any drawbacks or compromise.
Rim widths range from anything 50mm up to crazy beamers of 100+mm wide. You really do need to match your tyre width to your rim width very carefully. It’s this aspect that can end up being costly if you dive in to purchasing a fat bike too eagerly without doing your research. Fat bike wheels aren’t cheap.
For 4in tyres you need to pair them with rims of between 60-80mm wide. For fat bikes with tyres wider than 4in, rim width is a complicated business where single millimetres have an pronounced effect. Needless to say, for 5in tyres we’d recommend not going over 100mm in rim width.
Unlike on regular mountain bikes, where we would always recommend tubeless, with fat bikes ‘going tubeless‘ is easier said than done and the benefits are minimal at best. Sure it can save a bit of weight but not that much. And the extra heft of fat rubber is actually part of the ride experience and performance. WOOMPH-ing your way across the landscape is a big part of the experience.
So although you can go tubeless, it can be very hard getting tyres to seal and may require considerable outlay on special equipment.
It’s almost not worth even thinking about tyre tread pattern and design. The sheer footprint of fat tyres is what generates the traction. Err on the side of minimal knobbles.
As for sidewalls and tyre weight, don’t be tempted with the lightest tyres you can find. They just don’t ride very well. They wibble around and deflect like mad. They also offer no damping whatsoever to counter bike bobbing.
It may feel bizarre talking about suspension when dealing with fat bikes but, as we said above, fat tyres are not an alternative to suspension. Suspension and fat tyres do two very different jobs. A suspension fat bike is not a pointless thing.
A 4in tyre is not an alternative 4in-travel suspension fork.
Fat tyres are about amount-of-rubber in contact with the ground. Fat tyres use their size to deform under pressure (from above and below) to increase the amount of tyre adhering to the trail. They aren’t there to absorb rough stuff.
Fat tyres are not for soaking up bumps (although they do soak up small trail buzz admittedly). Loads of people assume that’s what fat tyres do. It isn’t correct.
Think of fat tyres for traction and suspension for control. Suspension has damping. Suspension is still the thing for controlling the immediate after-effects of large external forces (bumps, hard corners, G-outs etc).
So, as with regular hardtail mountain bikes, feel free to go for one with a suspension fork. We’d actually strongly recommend it if you want a fat bike to be your only/main bike. RockShox and Manitou are the names to look out for here.
That said, if you’re merely fat-curious or want a fat bike to become part of your fleet of available mountain bikes, there’s a lot to be said for saving money (and weight and servicing) and going for a rigid fork fat bike.
Hubs and bottom brackets
The elephant in the room of fat bikes. Hub and bottom bracket standards are all over the place. Because you can’t fit those oversized tyres into regular mountain bike frames and forks, this has resulted in a lack of consistent approach to hub widths and also bottom brackets (cranks have to be set wider apart to fit either side of the expanded rare stays).
It many it’s probably best to not worry too much about it. Whatever you go for you’ll be left stranded. There’ll be spares and upgrades for all standards for quite a while yet.
That said, if you want to leave the option of running a suspension fork at some point, get a fat bike with 150 x 15mm front hub.
The rear hub width that appears to becoming the most common is 197 x 12mm. In some ways this is a bit of shame as it leads to really special wide Q-factor cranks (think: John Wayne) but that’s the way it appears to be going.
Some notes about Q-factor. Regular mountain bikes have a Q-factor of around 170mm. Modern fat bikes are coming with Q-factors hovering around 200mm.
Despite what anyone may try to tell you, frame material has only one effect on the bike: weight. There is simply no way that any inherent ride characteristic of the chosen frame material is detectable through 4 inches of rubber.
Go carbon if you have the funds and want to save weight. Go titanium if you have more money than sense and like the look. Otherwise just go for an aluminium or steel frame fat bike.
Due to their snowbike heritage – and current wilderness bike wannabe status – you can sometimes find cable actuated disc brakes on fat bikes.
Not to beat about the bush, cable disc brakes suck. Their one and only advantage is that the can be mechanically/agriculturally bodge repaired if they go wrong in the middle of the Artic Circle. Are you going to be riding in the Artic Circle? No. Get hydraulic disc brakes.
Some fat bike retailers
Some popular fat bike models
Surly Ice Cream Truck
Salsa Beargrease Alloy
How much to spend on fat bike
You get what you pay for, as with all things in life. You will find fat bikes being knocked out for very tempting prices. Much like with niche bikes like fixies, singlespeeds and even arguably BMXs, the cheap option is very tempting. The problem is though, they won’t ride very nicely and they won’t last very well. At one point does a £500 fat bike you bought ‘for a laugh’ turn into a wreck or money-pit project?
We’d strongly recommend looking at fat bikes nearer the £1000 mark. From a recognisable and reputable bike brand (you’ll find almost every bike brand has a fat bike or two lurking in their range). And purchase it via a proper bike shop who will help you set it up and sort out obscure spares etc.