Monday, February 06, 2023

RoadTrailRide: Borealis Flume and Crestone Fat Bikes Reviews

Article by John Tribbia & Jeff Valliere

Borealis Flume and Crestone Fat Bike Reviews ($2,257 for Flume & $4,217 for Crestone as tested)

Borealis Crestone

Sizes: S(15”), M(17”), L(19”), XL(21”)


Based in Colorado Springs, Colorado, Borealis Fat Bikes is a company that specializes in manufacturing high-quality fat bikes, which are bicycles with extra-wide tires that are designed for riding on snow, sand, and other challenging terrain. The company was founded in 2009 by Steve Kaczmarek, who was inspired by the growing popularity of fat biking and saw an opportunity to create a line of high-performance fat bikes.

Kaczmarek had a background in bicycle manufacturing and had previously worked for a number of companies in the industry. He used his experience and knowledge to develop a line of fat bikes that were lightweight, durable, and capable of handling a variety of terrain.

Borealis Fat Bikes started wide distribution in 2013 and quickly gained a reputation for their high-quality and innovative designs. The company has since grown rapidly. Today, Borealis Fat Bikes continues to produce a range of high-performance fat bikes that are popular with riders all over the world. The company is known for its attention to detail and its commitment to quality, and its bikes are known for their durability and versatility.

They are truly top of the line in fat bikes. The Crestone model is their carbon frame bike and is as good as it gets, while the Flume is the aluminum version retaining nearly the same geometry and is a capable beast of a bike as well. Jeff V tested the Crestone while John tested the Flume. 

Both bikes were spec’d with high quality components and ready to ride upon delivery. Speaking of delivery, Borealis is a true family business with our bikes being hand delivered by Steve’s son who traveled from Colorado Springs to the Boulder area with a trunk full of fat bikes and delivered them directly. 

Above, our review sample Crestone on the left, plus my friend Simon’s Crestone on the right, a muddy day!


Jeff:  Lightweight build, the highest quality carbon craftsmanship, attention to detail, rugged durability, versatility (a great bike on and off the snow), agile, responsive geometry

John: perfect for riding on snow, loose dirt, and other challenging terrain; lightweight and nimble that is easy to maneuver and control; surprisingly fast and agile; comfortable and upright riding position that is good for long rides; customizable range of high-quality components


John: Some riders may find the bike to be on the heavier side; depending on how you choose to spec the bike, it could get pricey

Jeff: I really cannot come up with a con, this bike is awesome!  

First Impressions:

The Flume tackling a perfect condition day on the Front Range of Colorado

John: Overall, I was very impressed with the Borealis Flume Fat Bike. The bike is well-made and durable, and it is super stable while riding on snow, loose dirt, and other challenging terrain. It has a comfortable and secure feeling ride thanks to its low center of gravity and slack head tube angle. The rigid carbon fork provides sufficient shock absorption and control, making the bike feel planted and confident on rough trails. The drivetrain is smooth and reliable, with a 1x12 wide range of gears for climbing and descending. The hydraulic disc brakes offer excellent stopping power in all conditions, and the tires provide good traction, grip, and dampening of harsh terrain. 

In addition, I love that the lightweight, 6000-series aluminum frame comes with 2-3 bottle cage mounts, rear rack mounts on the seat stays and Lizard Skin protectors on both the down tube and drive-side chainstay. The placement of those protectors are a clear sign of the attention to detail Borealis puts into their designs – I find those areas get beat up really quickly. Similarly, there is internal cable routing for the dropper post, front derailleur, and the front + rear through axles, which makes the frame look sleek and free of any errant cables.

Jeff:  Right off the bat I was in awe of the Borealis Crestone.  One quick lift of the bike, I was amazed at how light it feels, at just 26 lbs for a size medium, fat tired bike, I could hardly believe it.  

The green colored carbon fiber Crestone frame has a deep and textured look to it, sparkling in the sun and changing almost as if magic in different lighting conditions and sun angles.  The construction, design, geometry and angles of the frame and fork make it clear that the folks at Crestone really know what they are doing and have not only supreme frame building skills, but have a keen sense of blending high performance and practicality.  The bike is a work of art.


John: On snow, the Flume performs incredibly well, with the wide tires providing good flotation and traction. The rigid carbon fork helps to smooth out the ride and improve control on slippery surfaces. I personally prefer having a rigid fork as opposed to front suspension, because I like feeling the snowy terrain underneath. Not to mention, the fat tires do an outstanding job of dampening any moderate bumps and offering some compliance to the ground. 

Despite the appearance with its huge tires, the Flume is really agile and nimble, making it a good choice for winter riding and dry trails. Here in the Front Range of Colorado, the mix of terrain and conditions is a perfect setting to test the versatility of any mountain bike, especially a fat bike. I was able to take the Flume on dry dirt, rutty dried out mud, fresh packed snow, and melted out frozen snow. To be frank, the bike handles all of those conditions really well. It floats atop the unstable terrain like snow and loose dirt and yet can dig into mud or wet snow.  

I would be remiss to not also mention that I really enjoyed how it rides on flat hardpack dirt or road – It goes a lot faster than I would have guessed. I think one reason is that Borealis designed the bike to have a standard cross country mountain bike frame geometry. I love climbing and I found the compact geometry generates a stiff push off on the incline. It felt really familiar to ride and I didn’t require any acclimation. In fact, I think the Flume would be an excellent entry level mountain bike for any aspiring rider, since it offers the same comfortable fit and a lot more traction and stability. The short stem and wide handlebars help with handling and confident riding. 

Jeff:  John sums up the ride quite well and I agree on all points.  The frame geometry is steady, stable, efficient, yet quick and agile without feeling twitchy.  The shorter stem and wide bars aid in excellent maneuverability and steering confidence.  I too love to climb and the Crestone performs amazingly well, in part because of its geometry and also its stiff frame that allows all of the rider’s power to be transmitted with no wasted energy.  Weighing only 26 lbs certainly helps as well.  The fat 4.3” tires in 27.5 circumference certainly help smooth the ride and I found the ride to be smooth on most snowy surfaces and most other mildly technical surfaces.  I was able to test the Crestone on just about everything from smooth packed snow, deep snow, slush, mud, frozen foot print holed snow, dry dirt smooth singletrack, rocky technical trails and some fast, somewhat rough (rough at speed) downhilling.  

While I think the rigid carbon fork is appropriate for most situations, I found that when riding higher speed bumpy downhills, I got bounced around a good bit, reminding me of riding fat tired 3 wheelers back of the 1980’s.  Certainly not a knock on the Crestone, but just the nature of riding a fat tire bike too fast.


John: The Borealis Flume has a comfortable and relaxed fit, with a roomy cockpit and upright riding position. The bike is designed to be versatile and accommodating, with a wide range of riders able to find a comfortable position. I’m 5’6” and have a short torso. I would characterize the fit as compact with precise handling abilities. Similar to other hardtails like the Pivot LES 2 or the Specialized Epic HT, the Flume has a comparable reach. Moreover, the geometry of the bike puts your body over the pedals, ensuring optimal pedal position for power and speed. 

The dropper seat post that was added to our bikes was the first time I’ve used the technology. It was incredibly useful for on-the-fly adjustments and was quite precise. 

Jeff:  John sums up the specifics of the fit well and I have the same overall impressions.  I am 5’9” tall, but have a 34” inseam and short torso.  The size medium/17” fits me well and reach is just right with the 50mm stem, putting me in a comfortably upright position without feeling stretched.  

With my long legs, I have the seatpost maxed out for most riding, though I often use the dropper post to lower my position an inch or two if things get technical or if I am having to hop on/off in difficult riding conditions.  

This is my first introduction to a dropper post and was only vaguely aware of them, until Matej Mahoric’s historic victory at Milan San Remo last year where he used a dropper post to his advantage for his aggressive attack down the Poggio.  While I will not be pulling off any downhill road bike attacks anymore, having a dropper post to me is a real advantage, always being able to optimize your seat height to match the terrain.  I did occasionally find myself confusing the dropper lever for a front derailleur lever, as I am not used to riding a 1x.  One other advantage I found with the dropper is that if you share your bike, it is easy to make a quick adjustment, as I let my wife and daughters ride the Crestone on occasion.  

My daughter who is 5’3” loves riding the Crestone and it actually fits well in  the size medium with some room to grow (the dropper post helps a lot).  If I were to keep the bike, she would probably take it over, as it was hard to wrestle it back from her.  She could write her own review.

Specs and Tech:

Standard Build Specs (Flume Build Options / Crestone Build Options)




Eagle NX

Eagle GX


$2,257 USD

$4,217 USD




Frame Material






Crank Arms

175mm Alloy

175mm Alloy

Rear Derailleur

RD ENX 1 x 12

RD ENX 1 x 12





PG 1230 11-50

PG 1230 11-50





SRAM - Select

SRAM - Select

Chain Ring

SRAM 30T X-Sync

SRAM 30T X-Sync


Borealis Flume Alloy

Borealis Crestone Carbon


Borealis Carbon Rigid Fork

Borealis Carbon Rigid Fork





Borealis: Front 15×150 Rear 12×197

Borealis: Front 15×150 Rear 12×197


26" or 27.5" Sun Ringle Mulefut V2

26" or 27.5" Sun Ringle Mulefut V2


Borealis Straight Gauge

Borealis Straight Gauge


Borealis Silver Brass

Borealis Silver Brass


Your Choice

Your Choice


Borealis Carbon Bar (35mm)

Borealis Carbon Bar (35mm)


Borealis 50mm or 70mm

Borealis 50mm or 70mm


KS LEV Inegra Dropper (add-on)

KS LEV Inegra Dropper (add-on)







Bottom Bracket

SRAM DUB 100mm

SRAM DUB 100mm

Both bikes we received to review were amazingly well spec'd. The Crestone came with a full SRAM Eagle GX 1 x 12 spd group set which provides amazingly clean, crisp and accurate shifting. The Flume was set up with SRAM Eagle NX 1 x 12, which was incredibly performant. 

The 12spd cassettes have an incredible 10-50 range (with a 30T front).  This combo is adequate for most of the riding that we’ve done and surprisingly did not wish for a double or triple chainring up front.

Up front on the Crestone we have a SRAM Eagle DUB GX crankset made of forged aluminum, which is light and stiff, coupled with a SRAM DUB bottom bracket that gives no flex.  The Q factor is quite wide here, but was not particularly noticeable.  The Borealis platform pedals are broad with a secure grip.


Likewise, the Flume came with a SRAM DUB NX Crank that felt powerful and stiff under the hardest pedal strokes. 

Jeff: For most snow riding, I went with the platform pedals as I wanted to wear a warmer shoe than my Sidi Dominator shoes, though when it was warmer and dry, I went with clipless for better efficiency.

The carbon Borealis GLOSS bars are wide and sturdy, offering very good control and additional dampening.

Holding the stem in place is a 35x50BLK Borealis branded stem, which is stocky and strong.

The SRAM Eagle GX (Crestone) and NX (Flume) 12spd rear derailleurs accommodate a wide range of gears and provide smooth and positive shifting under any load. They are quick and efficient, especially for the lazy shifter (ahem, John) who forgets to get in an appropriate climbing gear when the terrain steepens.

The SRAM Eagle 12spd trigger shifter and Guide RS G2 brakes on the Crestone make for a great combo, with the shifters being easy to operate with a mitten, as well as positive lever activation and modulation.

The SRAM NX trigger shifters and Level T hydraulic brakes on the Flume posed no problems and brought confidence in my shifting and braking in warm and colder weather. 

The disc brakes are very grabby, but modulate very well with an easy lever pull and positive feel.

The KS LEV Integra dropper post with KS Southpaw lever is easy to use with a wide range, super smooth and secure.

Dropper lever above.

The tires are Terrene YKY 27.5 x 4.3 Yipee Ki Yay, which offer excellent flotation and traction on loose surfaces, yet roll surprisingly well on hard surfaces. 

The Flume came with Mulefoot 26 x 80 wheelset and Terrene Cake Eater 26x4.6 tubeless tires. The combo is light and sturdy. With both wheelsets, we were both surprised at how quick the bike felt on flat concrete. 

The rims are HED Big Deal Alloy 27.5 x 80, which are wide, but crazy light and have surprisingly efficient rotating weight for the size.

While not made for mud, the Crestone handled it like a champ!

Conclusions & Ratings:

John: The Borealis Flume Fat Bike is a stable, surprisingly nimble, fat tire mountain bike that can tackle any type of terrain you throw at it. Because it performs well in snow, loose dirt, and technical terrain with reasonable vertical compliance and also performs well on harder surfaces such as dirt roads, I find it to be a nice versatile option for all types of riders. In fact, it is an excellent bike for newer mountain bike riders who desire greater stability and traction. Moreover, the range of gears on the 1x12 drivetrain ensures no climb is too steep. 

This bike is suited for endurance enthusiasts, weekend warriors and the serious brave-the-cold rider who will take to the snow on any occasion. At $2,250 in the base model, it is reasonably priced for a hardtail and it comes equipped with high quality components and a lightweight frame! While I would still prefer a traditional hardtail for summer months, I do like that the Flume is able to go anywhere at any time.

Ride - 9.5/10 (surprisingly fast, stable, and compliant on the bumpy stuff)

Fit - 10/10 (I made zero adjustments after finding the right saddle height)

Specs - 9.5/10 (top quality for their entry level version)

Fun Factor (out of 5) - 🙌 🙌 🙌 🙌 🙌

Overall Average: 9.7 / 10

Jeff:  I cannot say enough good things about the Borealis Crestone.  The frame quality and craftsmanship, attention to detail, well thought out features and componentry make Borealis the obvious choice if you are in the market for the best Fat Bike money can buy.  It is incredibly lightweight with efficient geometry which makes it exceptionally easy to ride.  The owners/staff are very easy to work with and attentive. They really know their game and I will be sending potential buyers their way for the indefinite future.

Ride - 10/10 

Fit - 10/10 

Specs - 10/10 

Fun Factor (out of 5) - 🙌 🙌 🙌 🙌 🙌

Overall Average: 10 / 10

Tester Profiles

John Tribbia is a regular technical reviewer for running-oriented product testing website RoadTrailRun with a large readership domestically and internationally. He has other writing about NAAWK Sunscreen and Yuba Cargo E-Bike (Part I, Part II, Part III, Part IV). 

He dabbled in bike racing both mountain and road as a junior Cat 5 and eventually upgraded to Expert on the mountain bike. After his brief stint of cycling racing and once in college, John crossed over to running and found success as a sponsored mountain/trail runner by placing atop the podium in domestic and international races. But he always kept his bikes nearby for cross training while injured, supplemental training, and commuting. Given that cross-over experience as well as 6+ years of working at University Bikes in Boulder, CO and over 20 years of competitive running, he loves the opportunity to test the latest and greatest in both sports. 

Jeff Valliere has been around bikes his entire life, as a toddler following his dad to bike races and bike shops, BMX racing as a kid, working in bike shops as a mechanic for 14+ years (10 at U-Bikes in Boulder where he met John) and racing as a professional road cyclist for several years.  Jeff no longer races, but still loves to ride as he introduces his daughters to the joys of cycling.  In addition to being obsessed with cycling, he runs mountains daily and has been reviewing running shoes/gear/tech for RoadTrailRun since 2015 and for other publications/companies since 2005.

The Borealis Flume and Crestone were loaned for this review.

Samples were provided at no charge for review purposes. RoadTrail Run has affiliate partnerships (but not with Borealis) and may earn commission on products purchased via shopping links in this article. These partnerships do not influence our editorial content. The opinions herein are entirely the authors'.

More RoadTrailRide Reviews HERE

Comments and Questions Welcome Below!

RoadTrailRun may receive a commission on purchases at the stores linked in this article. 
Your purchases help support RoadTrailRun and are much appreciated. Thanks!

Men's & Women's SHOP HERE
FREE 2 Day Shipping EASY No Sweat Returns

EUROPE Men's & Women's SHOP HERE

Europe only: use RTR code RTR5ALL for 5% off all products, even sale products 


Men's and Women's SHOP HERE
  • 10% Savings Every Day*  5% Back in Rewards Cash
  • Test Run Shoes 90 Days Worry Free
  • Crazy Fast, FREE Shipping

Men's & Women's SHOP HERE

Men's & Women's  SHOP HERE

Men's & Women's  SHOP HERE

Men's & Women's SHOP HERE
Use RTR code RTRTOP4 for 5% off all products, even sale products

Men's & Women's  SHOP HERE

Men's & Women's SHOP HERE
FREE Shipping on most orders over $40

Men's & Women's SHOP HERE

Men's & Women's SHOP HERE

Men's and Women's SHOP HERE


Enjoyed this post? Never miss out on future posts by Following RoadTrailRun News Feed

Please Like and Follow RoadTrailRun
Facebook:  Instagram: @roadtrailrun
Twitter: @RoadTrailRun You Tube: @RoadTrailRun