The Eurobike has shown it, the Interbike trade fair in Vegas anyway. The fatbike boom that started two years ago continues to smoulder solidly, even if this niche product can hardly be described as a wildfire. Nevertheless, the speciality bikes have established themselves as a permanent fixture, as the now more than ample range on the market proves. Anyone who didn't yet have a chubby bike in their range of models was followed by a well-known manufacturer for the upcoming winter season at the latest. The parts market in the oversize section is also flourishing. The range of tyres, rims, forks and cranks has never been greater.
The 26-inch rims measure up to 100 millimetres in width, the tyres between 4 and 4.8 inches - this allows a tractor-like grip to be achieved with tyre pressures of around 0.5 bar. Thanks to the large contact area, the tyre sinks less deeply - whether on snow, sand or gravel. You virtually float over roots and stones instead of driving against them - rolling resistance, comfort and off-road safety are therefore unbeatable.
But of course, the advantages are also offset by serious disadvantages. For example, the fun of fat biking is directly related to the weight. Differences of up to four kilos brought the big
Comparison test in BIKE 1/2014
to light. The tyres and wheels are the central issue when it comes to the weight and function of a fat bike. Here, too, there are drastic differences of over two kilos, which has a huge impact on agility. Tyre pressure and the condition of the tyres also have a significant influence on the riding characteristics. If the tyre pressure is too high, the grip advantage is nullified - control and comfort are then a thing of the past. Another special feature is the Q-factor. In order to integrate the wide tyres into the frame, the cranks have to move outwards. If you are used to normal width cranks, the two to five centimetre wider fat bike cranks can cause knee problems on longer tours.
ALUMINIUM OR CARBON
As with every other type of bike, the weight of a bike is determined by your wallet. As soon as carbon comes into play, whether in the frame, rims or add-on parts, it becomes lighter, but quickly also exorbitantly expensive. Does the extra cost of the frame make sense?
A lightweight fat bike hardtail frame made of aluminium weighs around 1850 grams. In comparison, the lightest carbon frame in our last comparison test weighed 1629 grams. A relatively small difference. However, new frames (e.g. from Fatback or Specialized) are said to weigh around 1300 grams. A weight saving of 500 grams is therefore possible if you opt for carbon as the frame material. Whether this makes sense depends on your budget. If you can't draw on a full budget, you have to decide how to reduce the overall weight. The weight saving is more noticeable on the wheels than on the frame.
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WHAT DOES THE FATBIKE MARKET OFFER?
The fatbike market is basically divided into three different categories:
1. the completely unsprung models with rigid fork.
2. hardtails with suspension fork.
3. full-suspension fatbike models.
In addition to the price, the intended use is of course the decisive factor when choosing the right fat bike. If you don't just want to ride your fatbike on the beach or through snow-covered landscapes, you at least need a suspension fork that provides peace of mind.
1. hardtail with rigid fork:
Example Specialised Fatboy
When it comes to "particularly light" or "particularly cheap", there is no way around the rigid fork. The 6999 euro Fatboy S-Works from Specialized achieves the former with a weight of just 11.3 kilos including carbon rims. Compared to the most common fatbike suspension fork Rock Shox Bluto, a carbon rigid fork weighing around 700 grams saves around 1.15 kilos. If you want to retrofit your fatbike with a rigid fork with a suspension fork at some point, you should definitely make sure it has a compatible thru axle. The Rock Shox Bluto is based on a 15x150 millimetre thru axle. In addition, the frame should also harmonise with the usually longer installation length of a suspension fork.
Areas of application: A rigid fork only makes sense on moderate trails. Such models are only suitable for off-road use to a very limited extent. A suspension fork effectively prevents the bouncy feeling of undamped tyres and, in addition to more comfort, simply brings significantly more composure to the chassis.
2. hardtail with suspension fork: Example Canyon Dude
Most fat bikes on the market are a combination of hardtail and suspension fork. Depending on the equipment, the bikes weigh from 12.5 kilos. The Rock Shox Bluto suspension fork (approx. 1850 grams) with 80 to 120 millimetres of travel is currently the first choice. There are no cheaper, functioning suspension fork models. If you want something more exclusive, you can now get the stiff Cannondale Lefty for fat bikes or the 1100 gram Lauf Carbonara - but without damping. As the thick tyres react very sensitively to obstacles at only 0.5 bar, suspension forks on fat bikes can generally be ridden a little firmer.
Areas of application: If you are mainly travelling off-road, you should definitely not do without a suspension fork. A damped suspension fork effectively prevents the bouncing effect of the large-volume balloon tyres. Who wants to bounce over the trails like a bouncy balloon tyre?
3rd Fully: Example Alutech Fat Fanes
Fatbike fullys (e.g. from Maxx, Salsa, Bulls, 11Nine) are still quite a rare species and usually weigh between 15 and 18 kilos. Due to the limited space on the rear triangle, tyres up to 4 inches are often used. The Bucksaw Carbon from Salsa is the first carbon fibre fully and should remain under 14 kilos in the top configuration. In general, the question arises as to whether a purist fat bike that lives from tyre comfort rather than complex technology necessarily needs full suspension. However, if you don't care about weight and agility, a fat bike full suspension bike benefits from an extremely comfortable ride and reserves that make a specific line choice irrelevant even in rough terrain.
Areas of application: Difficult terrain, maximum traction and suspension performance are the keywords that characterise a Fatbike-Fully. The preferred direction: downhill. Active riding and longer climbs are difficult to realise.
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WHAT DO I HAVE TO WATCH OUT FOR?
Fatbikes not only require special frame designs, but also special add-on parts. Rims, hubs, forks, cranks and derailleurs are the interfaces that need to be considered on a fatbike.
The Q-factor describes the distance between the cranks. So that the chain can run past the wide tyre, the cranks inevitably have to be further apart. While normal cranks range from 164-174 millimetres, the narrowest fatbike cranks (Salsa, E13) start at 196 millimetres and can go up to 225 millimetres. A wide Q-factor can cause knee problems. Pay attention to ankle clearance.
Thru axle As with all other bikes, fat bikes also benefit from the increased stiffness of a thru-axle. While the Bluto suspension fork from Rock Shox comes with a 15x150 millimetre axle, there are two common dimensions for the rear triangle in conjunction with a thru axle. 12x177 or 12x197, which is often based on the recommended tyre width of rather slim 4 inches or super fat 4.8 inches.
Single or double? Single drivetrains are very popular with fat bikes because the thick tyres leave hardly any room for the chain and derailleur. As the outer diameter of a fatbike is at 29er level, the climbing gear should never be too large. If you also want to utilise the traction advantage on steep climbs, you should not fit more than 28 teeth. With a double crank and front derailleur adapter, a 22 tooth chainring is an even better choice.
Tyres Fatbikes traditionally ride on 26-inch wheels, which in combination with 4.8-inch wide tyres even exceed the diameter of normal 29ers. To keep the weight of the rotating mass on the outside low, Trek also offers 27.5x4-inch wheels and tyres as an option for its Farley fat bike. With a tyre weight of between 1 and 1.7 kilos, you should look for lightweight tyres with a particularly flexible carcass (120 TPI).
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ALTERNATIVES
But a little too fat? Or too heavy for touring? Then the bike industry offers alternatives.
You can think what you like about e-mountainbikes. But if you do, then e-assistance makes sense on fat bikes. The thick knobbly tyres on fat bikes not only provide traction, but often also weight en masse. In combination with e-assistance, the grip advantage can therefore also be utilised with ease uphill. Disadvantage: E-Fatbikes like to weigh over 22 kilos.
If you want to benefit from the better grip and comfort of thicker tyres, but shy away from the disadvantages such as weight and wider Q-factor, you should take a closer look at the mountain bikes in the new Plus format employ. With 2.8-3.25 inch wide tyres, plus bikes are closer to normal MTBs and are noticeably more agile. However, they offer more comfort, traction - and therefore safety - particularly on demanding terrain. The range of hardtails and fullys is already very large.
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WHERE IS THE TUNING POTENTIAL?
Tyres are the decisive factor on a fat bike. To exploit the full potential, the tyre pressure must be set meticulously. 0.1 bar already makes a big difference on a fat bike. It is therefore essential to use a digital tyre pressure gauge.
Tubeless Not only the tyres, but also the inner tubes weigh quite a bit at 400-600 grams (each). Fortunately, there are already tubeless-compatible tyres that can be sealed with around 150 millilitres of latex milk. As there are currently no special tubeless kits for fat bikes, you have to seal the often holey rim with a wide, airtight adhesive tape. When inflating, a powerful compressor is required until the wide tyres jump cleanly onto the rim with a fairly loose fit. This tuning measure can save up to 900 grams. Some tyre manufacturers are already working flat out on lighter tubes weighing around 150 grams.
Spikes Fatbikes were originally developed to ride in places where normal mountain bikes cannot go - snow, sand, deep mud. While the thick tyres still offer pretty good grip on compact snow, it's also the end of the road on black ice. The tyre industry has developed special studded tyres for this area of use. For example, the Dillinger 5 from 45NRTH. With a fine, foldable 120-TPI carcass and 258 aluminium/carbide spikes for 250 euros (per tyre).
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"I like the hovercraft feeling of fat bikes." - Interview with Michael Staab, Product Manager Canyon
What do you see the fatbike being used for?
For me, the fatbike is not a special winter bike, but rather a trail bike. With the right key data, it can be used for a very wide range of applications. And even if I can't really justify it objectively, I really enjoy fat biking.
What points should you pay particular attention to on a fatbike?
The weight, especially that of the wheels, is extremely important and has a huge influence on the handling. A 4-inch tyre is enough for me. I personally don't need the extra traction of a wider tyre, but I do feel the increased weight. A narrow Q-factor also makes sense. With some fatbike cranks, the ankle clearance is also very small.
Aren't plus bikes in direct competition with fat bikes?
Plus has nothing whatsoever to do with fatbikes. The differences are too big. What I like about fat bikes is the hovercraft feeling. The low tyre pressure means you almost float over the trail and therefore roll incredibly easily off-road. This feeling is much less pronounced on plus-size bikes. On the other hand, more active riders have more fun with the more agile plus bikes.
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