Borealis Carbondale 27.5 x 50mm – Maxxis FBR/FBF (Plus/Fat) Wheel Review

“What my fat-bike did on summer vacation”

Back in April, we published a comparison of 4 sets of wheels (Two 26″ & Two 27.5″ options) with the goal of demystifying how 27.5″ rims and tires compare with their 26″ counterparts. I was especially interested in learning how tall each of the four wheelsets measured along with all of the other data points on each wheelset. This is the review of one of the wheelsets that we featured in that four-wheel comparison.


“My Fat-Bike became a Mountain Bike over the Summer!”

The wheel-build starts with a Borealis Carbondale double-wall carbon set of hoops that are 50mm wide, laced to a set of Borealis hubs with a set of Maxxis Minion FBR/FBF 27.5 x 3.8 tubeless tires. This is the set of wheels that I’ve ridden all summer mounted on a Fatback Corvus FLT. These wheels are the missing link, where plus and fat come together in what I think is the sweet spot for optimizing a rigid fat-bike for our particular regional Great Lakes singletrack.

Glacial River MTB Trails

These wheels and tires are just a little lighter, 3/8″ taller and 16mm narrower than a 26 x 4.0 Husker set up on an 80mm wide Reynolds carbon rim. The 50mm width of the Carbondale rim creates a nice round tire profile that is a mere 85 mm wide. The Minions have a lower sidewall profile with a proven tread pattern that inspires confidence in slick singletrack corners and root strewn climbs.


One of my favorite places to ride is the connector trail out at Kettle Moraine. It’s usually uncrowded and it has everything from baby heads to patches of loose sand. The Plus/Fat set up of these wheels provide all the flotation that you need to get through those sandy spots all while maintaining your speed. When the trail gets rough the lower profile of the Minions aren’t as bouncy as a good 26″ singletrack friendly fat-bike tire. These wheels and tires never let me down. They grip in the corners and climb like a goat. About the only knit that I can pick is that the tread on the Minions doesn’t shed mud very well. In the region where I ride, the singletrack systems are all closed when it’s wet so mud shedding isn’t very high on my priority list – YMMV.

Levis – Clarence Overlook

If you can’t tell…I’m sold on this 27.5 – 45-55mm wide plus bike rim with low profile 27.5 x 3.8 fat-bike tires for summer singletrack. I spent the previous two summer seasons riding a 29+ rigid hardtail and I can definitely say that I like this setup better. If you think that an 85mm tire is too wide for your needs, you can always mount any 27.5 x 2.6. 2.8, 3.0 or 3.25 tire to these (or similar width) rims. I’m told that it’s common sense to only run as much tire as you need and with all of the choices available currently, we have the ability to fine-tune our wheels to a wide variety of ride situations – now better than ever. For me…this setup combines the best attributes of both plus and fat for firmer substrates (like dirt). This might be the best upgrade/modification to enhance summer singletrack for a rigid fat-bike. For soft conditions like snow or beach rides, I would want something that provides more flotation, but for trail riding, this setup is tailor-made to rip!

Let’s get loaded and stay out all night!

These wheels earned 4.5 out of 5 flaming gnomes.

We ran between 7.5 and 10 PSI for dirt and 12 PSI for gravel during testing. The wheels set up very easily tubeless with 4 oz of Stan’s and over the four months of testing, never failed in the garage or out on the trail (zero-flats).


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4 Responses to Borealis Carbondale 27.5 x 50mm – Maxxis FBR/FBF (Plus/Fat) Wheel Review

  1. Erv Spanks September 19, 2018 at 10:48 am #

    Every time I have a question about this set up, I double check your article and you’ve answered it, thanks!

  2. Squatch September 24, 2018 at 12:58 pm #

    Thanks for the review. I’m looking at summer options for my Beargrease and I’m torn between this setup and 29+ (29 x 3 x 50mm). The 50mm doesn’t seem like it’s enough rim for a 3.8 – 4.0″ tire and I’d worry about the sidewalls getting squirmy. There are no carbon 27.5 65mm rims available so I’m likely going 29+. Thoughts & advice are welcome, thanks!

  3. Tim Mallard June 12, 2021 at 6:02 pm #

    Thanks for writing this article! It inspired me to build up my own Duroc 50mm wheel set for my Salsa Beargrease. I dressed up my 2016 fox 34 plus fork to look like a 1997 Judy SL. After so many years of DH i never thought I would have so much fun on a fat bike. But Im hooked now year round!

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