Not long after the first production plus bikes started popping up, fat bikers began to experiment with plus tire sets ups of their own. The goal was pretty straight forward – extend the seasonality of your fat bike by adding narrower rims and tires better suited for summer or hardpack riding. One of the biggest hindrances however was the need for multiple, likely custom, wheelsets to make it happen. That got the folks at Otso thinking. What if you could run both plus and fat tires without changing any parts other than the tires themselves? With that, the Plus-Fat concept was born.

Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires? Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires?

Truthfully, the Plus-Fat idea is less of a concept, and more of a combination of already available parts. The idea was to take a set of wide, plus bike wheels like the Sun Ringle Duroc 50 and wrap them in either 27.5 x 4.0 or 27.5 x 2.8″ tires. Same rim, two very different tire combinations. Thanks to the introduction of the 27.5″ fat bike tire, this was finally a possibility. For the average consumer, the ability to change just the tires to have essentially two completely different bikes is pretty intriguing, and something I wanted to experience for myself.

Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires? Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires? Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires?

A fork in the road

What really kicked off the idea was the ability to use arguably a better, lighter suspension fork in the form of the Fox Factory F34 Plus. While the fork was never designed for use as a fat bike fork, it clears the Terrene Cake Eater 27.5 x 4.0″ tire on a 50mm rim making it a perfect addition to the build. Pro tip: when pushing the limits of any fork’s tire clearance, always make sure to check the tire clearance at full compression with the air removed from the fork. Just because it clears the arch, doesn’t mean it won’t hit the crown on bottom out.

However, before this review even got off the ground, we got word that the fork has been discontinued for aftermarket or OEM (for Otso at least) sales. Which is a shame, since it was one of the best features of this build. Armed with a set of plus tires, the Voytek really came into its own thanks to the lighter build and improved performance of the F34 compared to the competition.

Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires? Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires?

In all honesty though, this isn’t much of a surprise. The F34 Plus was built with much more tire clearance than it needed for Plus bike use, and now that the F34 29″ fork is available that will fit up to 27.5 x 3″ tires, well it’s not surprising to see it go the way of the Dodo.

But, there are still plenty of options to make this build work. First, there’s the possibility of finding one of the F34 Plus forks out there on the used market, in which case you can have exactly this set up. Otherwise, you’ll have to go with one of the dedicated fat bike forks on the market which will work just fine – only with a heavier final build.

Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires? Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires?

The tires

For the sake of this build, Terrene hooked me up with the Cake Eater in a 27.5 x 4.0″ Light casing, and their McFly 27.5 x 2.8″ plus tire in a Light/Durable combo.

Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires? Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires?

It’s pretty common to see tires measuring less than the claimed width, so it’s not surprising to see both tires measure less than the numbers on the sidewalls here. What is surprising is that the Cake Eater measured less than 0.1″ different than the same tire mounted to a 77mm fat bike rim. It was 3.75″ on the 77mm internal Whisky Carbon rim, and 3.67″ on the 50mm internal Duroc rim. In this case, you aren’t giving up a ton of width when mounting it on the smaller rim.

The McFly measured 2.71 meaning it’s just a smaller tire than claimed since you wouldn’t be mounting it on any bigger of a rim.

Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires?

Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires? Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires?

Weight wise, one of the biggest reasons to switch out the tires for the summer is the chunk of weight you’ll save. Depending on the casing, you stand to drop up to 449g per tire which is a lot of rotational and unsprung weight to be carrying around all season if you don’t have to.

Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires? Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires?

The biggest change in terms of tire performance with this set up seemed to be that the Cake Eater was a bit rounder in terms of profile. In terms of aggressive riding, this was actually a bit of an improvement thanks to the tire’s willingness to carve into the turns. However, in terms of pure flotation, this was a small drawback.

The McFly on the other hand felt very sure footed, and made the Voytek feel like a true plus bike – not a fat bike riding around on plus wheels and tires. Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires?

The wheels

Since we’re talking about the Otso Voytek Plus-Fat build here, the wheels were built to match the specs of the frame and fork. That meant a 177x12mm rear hub and a Boost 110 front hub, which isn’t exactly your average combination.

Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires? Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires?

While the Sun Ringle Duroc 50 rims were the main attraction, the res of the wheels featured a solid build with DT Swiss 350 hubs which resulted in build weights of 1190g for the rear and 1030g for the front with tubeless valves and tape installed. These are lighter than your average fat bike wheelset but not by a huge margin. However, there are plenty of ways to lighten the build if price was no object.

Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires?

The ride

I’ve spent a good portion of the summer riding my Otso Voytek with both tire set ups from the beaches of South Carolina, to the greasy trails of the Midwest. Obviously, without winter testing I can’t comment on the fat bike’s abilities in the snow, but over the years I’ve gotten quite experienced with comparative testing on loose sand where traction and flotation is even more important IMO.

Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires?
Just your average ride along side of a pod of dolphins.

Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires? Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires?

There’s no denying it, the smaller, rounder fat bike tires will impact the fat bike’s flotation – but not as much as you might think. I had no problem riding through sand that was so soft it’s hard to walk through let alone ride though, only with slightly more effort on my part to keep it up right. The trade off was a bike that was faster and more agile on the rest of the ride. What you give up in flotation, you make up in speed. It still felt like the Otso, only even more efficient. It mostly felt like the same fat bike I know and love.

Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires?

Surprisingly for me, the biggest change change came in plus bike form. I’ve ridden the Voytek with a few different plus tire and wheel configurations, and in terms of off road use, this was by far the best. I think a lot of that can be contributed to the improved performance and chassis of the fork up front along with the wide stance of the tires. Running the Otso Flip Chip in the shortest chainstay position, the bike truly felt like a mountain bike and not a fat bike. Of course, this is greatly influenced by the narrow q-factor of the Otso which if you haven’t checked out, you should.

Otto Plus-Fat: Can you make a fat bike a plus bike by only changing the tires?

Takeaway

So the million dollar question: who is this for? Ultimately, if you want to get more out of your fat bike with less space to store spare parts, this is for you. But, if you need the most flotation possible or simply don’t want to change any parts to ride all year, this is not your set up. The Plus-Fat isn’t going to replace full-fat bikes for me when the conditions warrant them, but if I was limited to one bike with one set of wheels, this is a great way to make an already versatile bike even more so.

otsocycles.com

15 COMMENTS

    • No doubt there would be a significant difference, but there’s a few mitigating factors:
      1. Measured sizes were 3.67″ and 2.71″, so less than 1″. And the relationship between tire width and tire height is not always 1:1.
      2. Tire sag on a 4″ tire at 6 psi will be a lot more than on a 2.8″ tire at 16 psi.
      3. The Voytek has an adjustable dropout that changes BB drop by as much as 4mm.

    • @kimbo – remember that 2.8″ and 4.0 are the width. you need to measure the radius of the wheel with tire mounted. The difference between the two would be your BB height change. Measure from the ground to the axle height or measure the circumference do your math and voila.

      I had a bike with Minion 27.5×3.8 on 85mm rims and something that was not a minion…can’t remember 29×3.0 on Duron 50mm and the BB height change was ~10mm taller on the 29.

  1. I was also wondering about the BB height difference would be – but with the actual tire size being .9″ (~22mm) and the amount of “squish” on the sidewall being less on a Plus tire than a Fat tire, I bet the actual B drop only changes about 1/2″ or so…

  2. It will be interesting to see how many bike manufacturers out there will make a fat plus gravel bike where you can fit all 3 different wheel diameter sizes on one bike frame so that you have a very versatile bike for gravel and fatbiking all in the one package

    • There are few things at play here that make the Otso unique – its relatively narrow Q-Factor, it’s carbon, and it’s got a bigger real hub. It’d be cool to see (reasonably priced) gravel bikes that could fit 275×4″ tires, or lightweight full suspension bikes that could do 275×3.8 or 29×3 on normal hubs. That’s the kicker, for me at least, is fitting a wide range of tire widths on easily sourced (and swapped between bikes) hubs.

  3. Interesting read but if you can’t get plus rims for fat hubs cause that would be “custom” where are you going to get a set of 110/177 wheels that are not custom? Or does this only work because Otso is making them so your stuck with whatever they give you? There are actually lots of fat hub plus rim combos available out there. I would also question the true usability of a the 4″ tire setup. Having run this exact rim/tire combo, it sucks in the winter for everything but the hardest of groomed trails.

  4. I did this exact thing with my Crust Scapegoat, except with Velocity Dually rims and Schwalbe Rocket Ron tires for the summer. In hindsight a slightly wider rim would’ve been better but I’m overall very happy with the bike!

  5. Good article. I finally had a set of 40mm nexties laced up to try 29+ for my Fatboy. It’s still fully rigid, and no dropper. Even though I ran HED big deal carbon wheels when fat, the switch to 29+ has been eye opening. It’s definitely faster and still plush, just not as spongy. Bottom bracket height is higher, but only took one ride on favorite loop to adjust. Rim weight of hed/nextie almost identical, so I only dropped about a pound off each wheel going from ground control 26/4.6 to chupacabra 29/3.0. I will likely only run the fatties now in real snow out here in CO. Options are good. Trying new stuff is good.

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