FLUME FRAME

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