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Adventure, Cycle / December 4, 2016

What’s the deal with fat bikes?

Written by: Andrew Winohradsky

Some time around the mid to late ’90’s, a weird eddy began to boil up in the stream of mountain bike evolution.

When competing in races like the Iditarod, Alaskan endurance mountain bike racers found they needed more flotation and traction on snow, ice, and tundra. So they began tinkering with bike design and running extremely wide tires and wheels on their bicycles.

As is the case with most early of mountain bike designs, the first fat bikes we DIY garage hack-jobs. They didn’t look great, but they worked.

That fat bike eddy has since grown into a rapid. Every year, the bikes gobble up a bigger percentage of mountain bike sales overall—some industry-folk predict they’ll make up as 20-25% of sales within a decade. Fat bike races and rides are now held all over the planet, including a Fat Bike World Championship race that drew more than 260 competitors last year.

The bikes are no longer hacked together in cold garages in Alaska; current fat bikes often feature modern day design-goodies like carbon fiber frame materials, top of the line suspension, and tire technology that allows even those massive tires to weigh in just grams above their traditional brethren.

Once something of a novelty, fat bikes have become a major force in the MTB market.

The fat bike was born in Alaska, where endurance racers tackle the snowy Iditarod course.

The pros

The primary asset of a fat bike is pretty obvious: the added girth of the tires provides much better flotation over soft surfaces like mud, snow, and sand. But fat bikes offer other advantages, and some can even be enjoyed on dirt trails.

One is traction. The larger volume fat bike tire is inflated to a much lower pressures than a typical MTB tire. This makes for a much softer and more malleable tire, which allows it to create a much larger contact patch by flattening and spreading out on the trail’s surface. More tire contact on the trail’s surface means more traction, which comes in handy on loose corners, steep climbs, and slippery rocks.

Fat tires also dampen the ride a bit. MTB tires actually offer a bit of suspension to the bike and rider by absorbing the shock of bumps on the trail. The jarring effect of large and/or successive impacts from obstacles on the trail can create problems for riders, even loss of control.

Because of the much larger volume and much lower air pressures, fat bike tires can absorb more shock. In most trail settings, the ride will feel much smoother on a fat bike and this generally gives riders more control.

The cons

Fat tires aren’t without drawbacks, of course.

With rare exceptions, fat tires won’t roll as fast as traditional MTB tires. More traction means more friction, which creates more rolling resistance. Fat tires also still weigh more than traditional tires, so it takes more effort for riders to accelerate, decelerate, and turn with them.

The suppleness of the fat bike tire can sometimes be an issue for high-level riders, who tackle technical terrain at high speeds.  The tires don’t offer as solid and firm of a base and support as a traditional volume tire, and they’re more susceptible to punctures and other trail hazards.

So-called "plus-size bikes" fill the gap between fat tires and traditional MTB tires.

Fat bike races have grown in popularity, but competitors in traditional events generally still opt for traditional bikes.

The fat bike’s (slightly) slimmer brother

In the beginning, there was a pretty big gap in fat bikes and traditional MTB’s in terms of speed-oriented performance on dirt. While the big tires did offer up added traction and a smoother ride, they were still slow rolling and slow handling.

Since fat bikes were originally designed to be ridden on soft surfaces (snow, mud, sand, etc.), they didn’t need advanced suspension. Thus, they had a tough time handling the impacts of traditional dirt trail riding.

Then came the “plus-size bike”.

Traditional MTB tires average around 2.2” in width and are mounted on a fairly narrow rim. Fat bike tires run about 4” in width and are mounted on very wide rims. Plus-size tires average around are around 3” in width.

By splitting the difference between fat bike and traditional tire widths, plus-size bike manufacturers get the best of both worlds. They’re able to borrow the added traction and damping capabilities of the fat bike, but with less of the rolling resistance and slow handling characteristics.

Plus-size bikes are designed to be ridden primarily on dirt, so their suspensions and frame geometries are more appropriate for traditional trail riding. The bikes ride much faster than fat bikes, with more traction and a smoother ride than traditional bikes.

So what should I get?

If you plan to ride on snow, mud, and soft surfaces, you’ll want a traditional fat bike.

On dirt? Many people in the bike world feel the industry has finally nailed it with the plus-sized wheel and tires combined with modern bike design. They claim that plus size bikes will soon replace the traditional MTB altogether.

The smoother ride and added traction of the plus-size bike are selling points for many riders. In certain circumstances, these bikes offer the best combination of speed and control. Plus-size bikes definitely don’t fall short in terms of frame and component quality, as many of the bikes are spec’ed exactly the same as their slimmer tired cousins.

But we still don’t see fat or plus-sized bikes on top of the podium in dirt trail races. And that’s a big indicator that they’re simply not the best bet when it comes to terms of raw speed. Experienced trail shredders, downhillers, or dirt jumpers haven’t yet ditched their already very capable whips for plus-sized bikes.

Bottom line: On dirt, you probably won’t win your local race series or bang out KOM’s on Strava with your plus-sized or fat bike. But that isn’t always the point. The unique riding experience these bikes offer have proven that they have a place in the MTB world, and obviously, for many riders, they are the perfect tool for the job of having fun!

about the author

Andrew Winohradsky

Andrew Winohradsky has been having a blast working and playing on two wheels his entire life. Starting with BMX and motocross as a kid, mountain bikes came into the picture in the early ‘90s.

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