Introduction to Project 27Plus – WTB Scraper rims and Panaracer Fat B Nimble tires

Originally posted on March 10, 2015 at 7:47 am

If the past decade is any indication, there may soon be as many tire sizes as there are gears in a cassette (though that is also growing year after year). 26 is too small. 29 is too big. 3.7 isn’t fat enough. 4.8 is too fat. Where will it end?

Perhaps it never will, but Dirt Rag has a long history of experimenting with new wheel and tire sizes, from 26/24 combos, through early 29ers, and onto one of the first 27.5 bikes.

Rocky Mountain Sherpa

Our first introduction to 27Plus came in the form of the Rocky Mountain Sherpa displayed at the 2014 Sea Otter Classic. Based on a Rocky Mountain Element full suspension 29er, it was outfitted with a set of super wide 27.5 wheels with big 2.8-inch tires from WTB. The wider and taller tires have roughly the same diameter as a 29-inch wheel, so it was able to fit in the Element’s frame and fork.

Fast forward a year and a the WTB Scraper rims and Trailblazer tires are headed to a bike shop near you soon, and a few other brands have followed suit with tires that fall somewhere between a “normal” size and a full fat bike.

We got our hands on a set of the WTB Scraper rims with an internal width of 45 mm—that’s twice as wide as a traditional rim. Built with the same double wall construction as WTB’s other popular TCS rims, it promises to be a simple tubeless setup when the tires become available.

Panaracer's Fat B Nimble tires will be available in 26x4, 29x3 and 27.5x3.5.
Panaracer’s Fat B Nimble tires will be available in 26×4, 29×3 and 27.5×3.5.

In the meantime, we also received a set of Panaracer’s new Fat B Nimble tires in 27.5×3.5. Eager to get this project started, I mounted them to the Scraper rims before the wheels have even been built. One of the key steps in this project is seeing how they will work with existing components, so we haven’t yet decided on which hubs to build them with. Out of the box the pair weighed in at 693 grams and 673 grams, so their weight is significantly lighter than fat bike tires and competitive with many cross-country tires.

First we mounted them up on the Scraper rims and grabbed the Feedback Sports calipers: Panaracer Fat B Nimble 27.5×3.5 on WTB Scraper rim (45 mm internal width) measured 71 mm wide and 73.3 cm in diameter.

UPDATE: Since I first posted this story the Fat-B-Nimbles have stretched out a noticeable amount. They now measure 74.3 mm wide.

Panaracer Fat B Nimble 27.5x3.5

If that seems small, it’s because it is—71 mm is about 2.8 inches, well short of the 3.5 inches marked on the sidewall:


Up against a normal 27.5 wheel and tire, however, they are quite a bit larger. A Schwalbe Hans Dampf 27.5×2.35 on a Easton Haven rim measured 57.5 mm wide and 71.4 cm in diameter.

27.5 Schwalbe Hans Dampf left, Panaracer Fat B Nimble 27.5×3.5 right.

So how does it compare to the other “mid-fat” size? I grabbed a 29×3 Surly Knard mounted on a Stan’s NoTubes Flow EX rim (25.5 mm internal width). It measures 73 mm wide and 77.4 cm in diameter:

Panaracer Fat B Nimble 27.5x3.5 vs. Surly Knard 29x3.
Panaracer Fat B Nimble 27.5×3.5 vs. Surly Knard 29×3.

For the sake of comparison, we also installed the Hans Dampf on the Scraper rim and the Fat B Nimble on an Easton Haven rim (21 mm internal width):

  • Panaracer Fat B Nimble 27.5×3.5 on Easton Haven rim: 65 mm wide, 72.5 cm in diameter
  • Schwalbe Hans Dampf 27.5×2.35 on WTB Scraper rim: 67 mm wide, 71.6 cm in diameter

As you can see from the numbers, the rim makes a bigger difference in the tire’s ultimate width, though it also dramatically changes the shape of the Hans Dampf, creating a flatter, more square profile than it was likely designed for. The Fat B Nimble is also much taller.

The Fat B Nimble is also far from optimal on the smaller rim, with its profile rounding off so far that the side knobs become essentially useless. However it did fit easily in a 27.5 Fox 34 fork when mounted on the smaller rim, and I have no doubt it will fit on the larger rim as well.

Panaracer Fat B Nimble 27.5x3.5 tire, Easton Haven rim, and 27.5 Fox 34 fork.
Panaracer Fat B Nimble 27.5×3.5 tire, Easton Haven rim, and 27.5 Fox 34 fork.

So what’s next? Step two is getting the Scraper rims laced up and see which bikes the wheels will fit in. A 29er with good tire clearance should be no problem. Will he bigger tires on a smaller rim perform well on the trail? That’s what we hope to find out. Stay tuned.


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