Borealis Flume Eagle NX

Borealis Flume Eagle NX
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All new for 2019! The 12 speed Eagle NX Flume is simply the best alloy Fat Bike on the market in its class. Sporting carbon bars, carbon seat post and carbon fork, this ride is ready to go into any adventure you can imagine. Standard wheelset includes HED single wall alloy rims ready for tubeless set up. Select the tire which best fits your season and terrane for maximum riding enjoyment. Named after trails in Breckenridge and a Class 5 drop along the Arkansas River, the Flume won’t disappoint!

Fatbiking adventurers know that inspiration matters, and a ride (or bike) is only as good as the idea that created it. The expedition-ready Flume capitalizes on all the sweetness of the Crestone, but does so in lightweight, 6000-series aluminum. Up mountains, down glaciers and across deserts, the Flume is ready for action.

There are all kinds of alloy fat bikes on the market, but none with the Flume’s purebred heritage. The custom tubeset mates ideal, high-performance geometry with competition-ready spec. But if pedaling across our blue planet is more your speed, the Flume will speed you through.


  • The Flume is built on an alloy frame that draws on all our experience in making fat bikes at a much lower price
  • All aluminum frame with careful attention to finish details
  • Borealis unique geometry for the best ride experience
  • Reduced stand over height

Based on our research, riders at the heights below will usually take the corresponding frame size. If you’re at a transitional height that spans two sizes, look at the geometry chart to get the Stack and Reach you like based on other bikes you are comfortable on.


Frame Borealis Flume Lightweight 6066 Alloy Frame
Fork Borealis Carbon Rigid Fork or Bluto RL (+$200)
Headset Borealis
Rims/Wheels Mulefut Alloy 26 x 80mm
Hubs Borealis: Front 15×150 Rear 12×197
Spokes Wheelsmith Black
Crankset SRAM Eagle GX Alloy w/30T Chain Ring
Chain KMC X12
Rear Derailleur SRAM Eagle NX 12 Speed
Rear Cogs SRAM PG-1230 10-50
Shifters SRAM Eagle NX 12 Speed
Brakes SRAM Level T w/Centerline 160/160
Saddle Borealis
Seat Post Borealis Carbon 31.6mm
Accessories & Extras Lizard Skins
Color(s) Orange/Black/Green
Sizes S, M, L, XL
Weight ~28lbs +2lbs for Bluto

* Subject to change without notice.

Part Numbers

Option MPN Store SKU
Small BIFB0021001 BIFB0021001
Medium BIFB0021002 BIFB0021002
Large BIFB0021003 BIFB0021003
X-Large BIFB0021004 BIFB0021004