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Flume Options

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With premium frame quality and only the best components, the Borealis Flume offers the best value on the market. This expedition-ready fatty mirrors the Crestone geometry, 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 and durability.

HIGHLIGHTS

  • Standard features include: SRAM Eagle NX 12-Speed drivetrain, SRAM Level T brakes, rigid carbon fork, carbon handlebars, carbon seat post, durable Sun Ringle Mulefüt rims and your choice of tires.
  • Frame geometry provides responsive handling, offering maximum control for varying conditions in snow or sand.
  • Tire clearance up to 26x5” and 27.5x4.5”.
  • Compatibility for 100-120mm of suspension travel for increased comfort and control.
  • Lightweight, 6000-series aluminum frame comes with 2-3 bottle cage mounts, rear rack mounts on seat stays and Lizard Skin protectors on both the down tube and drive-side chain stay.

    COMPATIBILITY

    • Rockshox Bluto Fork tire size limitations: 26x5” or 27.5x4”
    • Mastodon Pro EXT Fork tire size limitations: 26x5” or 27.5x4.5”
    • Borealis Rigid Carbon Fork tire size limitations: 26x5” or 27.5x4.5”
    • Dually 29x45 and 27.5x45 Rims – Max tire width: 3”
    • All rims 65mm to 85mm wide are compatible with tire widths of 3.8” to 5”
    • HED Carbon 100mm Rims – Max tire width of 4.8”

       

      ASSEMBLY

      If you choose "No Assembly" your bike will require complete assembly with an exception of the wheels. 

      If you choose "Assembled by Borealis", there is some assembly required upon receipt. Your bike will be completely assembled and tuned by Borealis, then partially disassembled for shipment. The remaining assembly will require installation of the rear derailleur, chain, fork, seat post, wheels, and handlebars. A multi-tool will be included with your order that has all tools necessary to assemble the bike, with the exception of a torque wrench. If you are not familiar with this level of assembly, we recommend having your local bike shop complete the assembly. Below is a video showing the remaining assembly once you receive the bike. 

      Assembly Video

      WHEELS & TIRES

      • All bikes come standard with tubes.
      • If you order rim tape with your Mulefut rims, we will tape the rims and install the tires with tubes.
      • HED Alloy and HED Carbon rims do not require rim tape for tubeless set up.
      • Tubes must be removed and tubeless valves installed for tubeless set up. We recommended to have this completed by a professional bicycle mechanic.

      BUILD SPECS

      Eagle NX Eagle GX Eagle X01 Eagle XX1
      Crankset SRAM Eagle NX SRAM Eagle GX SRAM Eagle X01 SRAM Eagle XX1
      Crank Arms 175mm Alloy 175 Alloy 175mm Carbon 175mm Carbon
      Rear Derailleur RD ENX 1 x 12 RD EGX 1 x 12 RD EXO 1 x 12 RD EXX 1 x 12
      Chain KMC X12 KMC X12
      KMC X12
      SRAM XX1
      Cassette PG 1230 11-50 XG 1275 10-52 XG 1295 10-52 XG 1299 10-50 Gold
      Shifters SRAM Eagle NX SRAM Eagle GX SRAM Eagle X01 SRAM Eagle XX1
      Brakes SRAM - Select SRAM - Select SRAM - Select SRAM - Select
      Chain Ring SRAM 30T X-Sync
      Frame Borealis Flume Alloy
      Fork Borealis Carbon Rigid Fork
      Headset FSA
      Hubs Borealis: Front 15×150 Rear 12×197
      Rims 26" or 27.5" Sun Ringle Mulefut V2
      Spokes Borealis Straight Gauge
      Nipples Borealis Silver Brass
      Tires Your Choice
      Bar RaceFace Next SL Carbon
      Stem Borealis 50mm or 70mm
      Post RaceFace Next SL Carbon 31.6
      Saddle Borealis
      Grips Borealis
      Bottom Bracket SRAM DUB 100mm
      DT/CS Protector Lizard Skins
      Weight See weight calculator for estimated weight.

       

       

       

      SIZE CHART

      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.

       

       

      GEOMETRY CHART

      Borealis offers four frame designs with unique fit and geometry to suit your every Fat Bike need. Begin by taking a rough size approximation on the chart below that is based on height, then select the corresponding bike with your fit needs by using the geometry chart further below. We recommend a similar fit to you mountain bike, so grab a measuring tape and dial it in.

        S M L XL
      EFFECTIVE TOP TUBE 585 mm 610 mm 630 mm 650 mm
      SEAT TUBE CENTER TO TOP 381 mm 432 mm 484 mm 534 mm
      HEAD TUBE 105 mm 120 mm 135 mm 150 mm
      SEAT TUBE ANGLE 73 deg 73 deg 73 deg 73 deg
      HEAD TUBE ANGLE 70 deg 70 deg 70 deg 70 deg
      STANDOVER HEIGHT Varies based on wheel and tire size
      CHAINSTAY 455 mm 455 mm 455 mm 455 mm
      BB DROP 60 mm 60 mm 60 mm 60 mm
      REACH 407 mm 423 mm 438 mm 451 mm
      STACK 597 mm 611 mm 625 mm 639 mm

       

       

      $1,499.00

      With premium frame quality and only the best components, the Borealis Flume offers the best value on the market. This expedition-ready fatty mirrors the Crestone geometry, 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 and durability.

      HIGHLIGHTS

      • Standard features include: SRAM Eagle NX 12-Speed drivetrain, SRAM Level T brakes, rigid carbon fork, carbon handlebars, carbon seat post, durable Sun Ringle Mulefüt rims and your choice of tires.
      • Frame geometry provides responsive handling, offering maximum control for varying conditions in snow or sand.
      • Tire clearance up to 26x5” and 27.5x4.5”.
      • Compatibility for 100-120mm of suspension travel for increased comfort and control.
      • Lightweight, 6000-series aluminum frame comes with 2-3 bottle cage mounts, rear rack mounts on seat stays and Lizard Skin protectors on both the down tube and drive-side chain stay.

        COMPATIBILITY

        • Rockshox Bluto Fork tire size limitations: 26x5” or 27.5x4”
        • Mastodon Pro EXT Fork tire size limitations: 26x5” or 27.5x4.5”
        • Borealis Rigid Carbon Fork tire size limitations: 26x5” or 27.5x4.5”
        • Dually 29x45 and 27.5x45 Rims – Max tire width: 3”
        • All rims 65mm to 85mm wide are compatible with tire widths of 3.8” to 5”
        • HED Carbon 100mm Rims – Max tire width of 4.8”

           

          ASSEMBLY

          If you choose "No Assembly" your bike will require complete assembly with an exception of the wheels. 

          If you choose "Assembled by Borealis", there is some assembly required upon receipt. Your bike will be completely assembled and tuned by Borealis, then partially disassembled for shipment. The remaining assembly will require installation of the rear derailleur, chain, fork, seat post, wheels, and handlebars. A multi-tool will be included with your order that has all tools necessary to assemble the bike, with the exception of a torque wrench. If you are not familiar with this level of assembly, we recommend having your local bike shop complete the assembly. Below is a video showing the remaining assembly once you receive the bike. 

          Assembly Video

          WHEELS & TIRES

          • All bikes come standard with tubes.
          • If you order rim tape with your Mulefut rims, we will tape the rims and install the tires with tubes.
          • HED Alloy and HED Carbon rims do not require rim tape for tubeless set up.
          • Tubes must be removed and tubeless valves installed for tubeless set up. We recommended to have this completed by a professional bicycle mechanic.

          BUILD SPECS

          Eagle NX Eagle GX Eagle X01 Eagle XX1
          Crankset SRAM Eagle NX SRAM Eagle GX SRAM Eagle X01 SRAM Eagle XX1
          Crank Arms 175mm Alloy 175 Alloy 175mm Carbon 175mm Carbon
          Rear Derailleur RD ENX 1 x 12 RD EGX 1 x 12 RD EXO 1 x 12 RD EXX 1 x 12
          Chain KMC X12 KMC X12
          KMC X12
          SRAM XX1
          Cassette PG 1230 11-50 XG 1275 10-52 XG 1295 10-52 XG 1299 10-50 Gold
          Shifters SRAM Eagle NX SRAM Eagle GX SRAM Eagle X01 SRAM Eagle XX1
          Brakes SRAM - Select SRAM - Select SRAM - Select SRAM - Select
          Chain Ring SRAM 30T X-Sync
          Frame Borealis Flume Alloy
          Fork Borealis Carbon Rigid Fork
          Headset FSA
          Hubs Borealis: Front 15×150 Rear 12×197
          Rims 26" or 27.5" Sun Ringle Mulefut V2
          Spokes Borealis Straight Gauge
          Nipples Borealis Silver Brass
          Tires Your Choice
          Bar RaceFace Next SL Carbon
          Stem Borealis 50mm or 70mm
          Post RaceFace Next SL Carbon 31.6
          Saddle Borealis
          Grips Borealis
          Bottom Bracket SRAM DUB 100mm
          DT/CS Protector Lizard Skins
          Weight See weight calculator for estimated weight.

           

           

           

          SIZE CHART

          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.

           

           

          GEOMETRY CHART

          Borealis offers four frame designs with unique fit and geometry to suit your every Fat Bike need. Begin by taking a rough size approximation on the chart below that is based on height, then select the corresponding bike with your fit needs by using the geometry chart further below. We recommend a similar fit to you mountain bike, so grab a measuring tape and dial it in.

            S M L XL
          EFFECTIVE TOP TUBE 585 mm 610 mm 630 mm 650 mm
          SEAT TUBE CENTER TO TOP 381 mm 432 mm 484 mm 534 mm
          HEAD TUBE 105 mm 120 mm 135 mm 150 mm
          SEAT TUBE ANGLE 73 deg 73 deg 73 deg 73 deg
          HEAD TUBE ANGLE 70 deg 70 deg 70 deg 70 deg
          STANDOVER HEIGHT Varies based on wheel and tire size
          CHAINSTAY 455 mm 455 mm 455 mm 455 mm
          BB DROP 60 mm 60 mm 60 mm 60 mm
          REACH 407 mm 423 mm 438 mm 451 mm
          STACK 597 mm 611 mm 625 mm 639 mm

           

           

          $1,499.00

           

           

          RIDER HEIGHT RECOMMENDATIONS
          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.

          GEOMETRY & SIZING
          Borealis offers four frame designs with unique fit and geometry to suit your every Fat Bike need. Begin by taking a rough size approximation on the chart below that is based on height, then select the corresponding bike with your fit needs by using the geometry chart further below. We recommend a similar fit to you mountain bike, so grab a measuring tape and dial it in.

           

            S M L XL
          EFFECTIVE TOP TUBE 585 mm 610 mm 630 mm 650 mm
          SEAT TUBE CENTER TO TOP 381 mm 432 mm 484 mm 534 mm
          HEAD TUBE 105 mm 120 mm 135 mm 150 mm
          SEAT TUBE ANGLE 73 deg 73 deg 73 deg 73 deg
          HEAD TUBE ANGLE 70 deg 70 deg 70 deg 70 deg
          STANDOVER HEIGHT Varies based on wheel and tire size
          CHAINSTAY 455 mm 455 mm 455 mm 455 mm
          BB DROP 60 mm 60 mm 60 mm 60 mm
          REACH 407 mm 423 mm 438 mm 451 mm
          STACK 597 mm 611 mm 625 mm 639 mm

           

           

           

           


           

          Wheel / Tire Size 26 x 3.8–5.0" on up to a 100mm rim / 27.5 x 2.8-4.5 on up to a 82mm rim / 29 x 2.25–3.0
          Susp Fork Travel 100-120mm
          Fork Offset 51mm
          Headset-Upper IS41
          Headset-Lower IS52
          Seatpost ø31.6mm
          Seat Collar ø34.9mm
          Dropper Compatible Internal - 125mm for SM & MD / 150mm for LG & XL
          Front Derailleur Type Not Compatible
          Bottom Bracket 100mm Threaded BSA 
          Crankset (Max Ring) Chainline 76mm / 1x (34t)
          Rear Brake (Rotor) 74mm post (160–180mm)
          Rear Spacing 197 x 12mm thru-axle
          Rear Axle ø12 x 229L, TP= 1.5, TL = 20
          Derailleur Hanger Borealis Custom
          Bottle Mount  SM : 2 (downtube) / MD, SM, XL: 3 (downtube & seatube)
          Rear Rack Reccomendation Old Man Mountain Divide Fat 
          Rear Rack Mounts, Upper Yes
          Axle to Crown 487mm
          Steerer Tube Size 28.6mm
          Steerer Style Tapered
          Crown Seat Diameter 40mm
          $500.00

           

           

          RIDER HEIGHT RECOMMENDATIONS
          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.

          GEOMETRY & SIZING
          Borealis offers four frame designs with unique fit and geometry to suit your every Fat Bike need. Begin by taking a rough size approximation on the chart below that is based on height, then select the corresponding bike with your fit needs by using the geometry chart further below. We recommend a similar fit to you mountain bike, so grab a measuring tape and dial it in.

           

            S M L XL
          EFFECTIVE TOP TUBE 585 mm 610 mm 630 mm 650 mm
          SEAT TUBE CENTER TO TOP 381 mm 432 mm 484 mm 534 mm
          HEAD TUBE 105 mm 120 mm 135 mm 150 mm
          SEAT TUBE ANGLE 73 deg 73 deg 73 deg 73 deg
          HEAD TUBE ANGLE 70 deg 70 deg 70 deg 70 deg
          STANDOVER HEIGHT Varies based on wheel and tire size
          CHAINSTAY 455 mm 455 mm 455 mm 455 mm
          BB DROP 60 mm 60 mm 60 mm 60 mm
          REACH 407 mm 423 mm 438 mm 451 mm
          STACK 597 mm 611 mm 625 mm 639 mm

           

           

           

           


           

          Wheel / Tire Size 26 x 3.8–5.0" on up to a 100mm rim / 27.5 x 2.8-4.5 on up to a 82mm rim / 29 x 2.25–3.0
          Susp Fork Travel 100-120mm
          Fork Offset 51mm
          Headset-Upper IS41
          Headset-Lower IS52
          Seatpost ø31.6mm
          Seat Collar ø34.9mm
          Dropper Compatible Internal - 125mm for SM & MD / 150mm for LG & XL
          Front Derailleur Type Not Compatible
          Bottom Bracket 100mm Threaded BSA 
          Crankset (Max Ring) Chainline 76mm / 1x (34t)
          Rear Brake (Rotor) 74mm post (160–180mm)
          Rear Spacing 197 x 12mm thru-axle
          Rear Axle ø12 x 229L, TP= 1.5, TL = 20
          Derailleur Hanger Borealis Custom
          Bottle Mount  SM : 2 (downtube) / MD, SM, XL: 3 (downtube & seatube)
          Rear Rack Reccomendation Old Man Mountain Divide Fat 
          Rear Rack Mounts, Upper Yes
          Axle to Crown 487mm
          Steerer Tube Size 28.6mm
          Steerer Style Tapered
          Crown Seat Diameter 40mm
          $500.00