$2,039.00
Flume Custom - Aluminum Fat Bike
0% APR up to 24 months with Affirm! Financing Options Available at Checkout.
Size Chart
Size Chart
Shipping and Returns
Shipping and Returns
Borealis does not accept shipments to PO boxes, and additional charges may apply for deliveries to Alaska and Hawaii. We offer flat rate shipping on all products through the most economical FedEx option.
Bikes, frames, and wheelsets typically ship via Ground, while small parts are shipped using 2-Day Express. Please contact us if any damage occurs during shipping.
Borealis provides a 30-day money-back guarantee. If you're not satisfied with your purchase, you can exchange the product or return it for a full refund, minus any transaction fees and shipping costs. Return shipping is the customer’s responsibility, and all returned or exchanged items must be in sellable condition.
LIMITED LIFETIME WARRANTY
LIMITED LIFETIME WARRANTY
LIMITED LIFETIME WARRANTY ON BICYCLE FRAMES & FORKS
FOR PURCHASES MADE ON OR AFTER JANUARY 1, 2023:
Original Owner
BOREALIS offers a LIMITED LIFETIME warranty to the original owner of each new BOREALIS bicycle, fork or frameset that the bicycle frame, fork or frameset when new is free of defective materials and workmanship.
Normal Conditions
The limited warranty is conditioned upon the bicycle being operated under normal conditions and use, and properly maintained.
Limitations
This limited warranty does not apply to paint/finish or components attached to the bicycle/fork/frameset such as rims, drive train, brakes, seat post, handlebar and stem, or any suspension related parts or components.
Paint/finish, components attached to the bicycle/frameset such as rims, drive train, brakes, seat post, handlebar and stem, or any suspension-related parts or components are covered under the limited one (1) year warranty.
Load Weight
The total cargo load for BOREALIS frames and forks is 300 pounds. The total cargo load includes the rider and any associated gear warn by the rider or attached to the frame or fork.
PURCHASES MADE BEFORE JANUARY 1, 2023 HAVE A 5-YEAR WARRANTY WITH THE SAME LIMITATIONS.
LIMITED ONE (1) YEAR WARRANTY ON COMPLETE BICYCLE
Subject to the following limitations, terms and conditions, BOREALIS warrants to the original owner of each new BOREALIS bicycle that this bicycle, when new, is free of defective materials and workmanship. This warranty shall expire one (1) year from the date of the original purchase from an authorized BOREALIS dealer and is conditioned upon the bicycle being operated under normal conditions and use, and properly maintained. This warranty is void if the bicycle was not purchased new or not properly assembled by an authorized BOREALIS dealer.
Click for Full Details Here
FOR PURCHASES MADE ON OR AFTER JANUARY 1, 2023:
Original Owner
BOREALIS offers a LIMITED LIFETIME warranty to the original owner of each new BOREALIS bicycle, fork or frameset that the bicycle frame, fork or frameset when new is free of defective materials and workmanship.
Normal Conditions
The limited warranty is conditioned upon the bicycle being operated under normal conditions and use, and properly maintained.
Limitations
This limited warranty does not apply to paint/finish or components attached to the bicycle/fork/frameset such as rims, drive train, brakes, seat post, handlebar and stem, or any suspension related parts or components.
Paint/finish, components attached to the bicycle/frameset such as rims, drive train, brakes, seat post, handlebar and stem, or any suspension-related parts or components are covered under the limited one (1) year warranty.
Load Weight
The total cargo load for BOREALIS frames and forks is 300 pounds. The total cargo load includes the rider and any associated gear warn by the rider or attached to the frame or fork.
PURCHASES MADE BEFORE JANUARY 1, 2023 HAVE A 5-YEAR WARRANTY WITH THE SAME LIMITATIONS.
LIMITED ONE (1) YEAR WARRANTY ON COMPLETE BICYCLE
Subject to the following limitations, terms and conditions, BOREALIS warrants to the original owner of each new BOREALIS bicycle that this bicycle, when new, is free of defective materials and workmanship. This warranty shall expire one (1) year from the date of the original purchase from an authorized BOREALIS dealer and is conditioned upon the bicycle being operated under normal conditions and use, and properly maintained. This warranty is void if the bicycle was not purchased new or not properly assembled by an authorized BOREALIS dealer.
Click for Full Details Here
Couldn't load pickup availability
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.
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 | |
| Frame | Flume (Aluminum) | Flume (Aluminum) |
| Fork | Borealis Carbon Rigid Fork Standard Option | |
| Bottom Bracket | SRAM DUB 100mm | |
| Crankset | SRAM Eagle NX Alloy 175mm w/ SRAM X-SYNC 30T | SRAM Eagle GX Alloy 175mm w/ SRAM X-SYNC 30T |
| Rear Derailleur | SRAM Eagle NX 12 Speed | SRAM Eagle GX 12 Speed |
| Chain | Eagle GX | Eagle GX |
| Cassette | PG 1230 11-50 | XG 1275 10-52 |
| Shifter | SRAM Eagle NX | SRAM Eagle GX |
| Brakes | SRAM Level T 2-Piston Hydraulic | |
| Rotors | SRAM Centerline 160mm | |
| Headset | FSA | |
| Hubs | Borealis GEN 4 Black 15x150 Front / 12x197 Rear | |
| Rims | Sun Ringle Mulefut V2 26x80 or 27.5x65 | |
| Spokes | Borealis Straight Gauge | |
| Nipples | Borealis Silver Brass | |
| Tires | Your Choice | |
| Bar | Borealis Carbon 35x760mm | |
| Stem | Borealis 50mm | |
| Post | Borealis Carbon 31.6x400mm | |
| Saddle | Borealis | |
| Grips | Ergon GA20 | |
| DT/CS Protector | Lizard Skins | |
| Weight | See weight calculator for estimated weight. | |
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 |
ASSEMBLY
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. Tires will be set up with tubes. Tubeless rim tape and valves are included on the side.
OWNER'S MANUAL
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”
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Customer Reviews
I looked at a ton of fat bikes, found a Crestone one size too small for me but on a big sale. Thankfully I looked on here and used the custom bike builder. I got exactly what I wanted, the newer Mastodon fork, and the weight shown on the builder was accurate! Totally blown away by this bike. As a Tig welder I really appreciate the effort they put into the frames they are beautiful. To top it all off, there is an integrated dropper port in the seat post! Couldn't get any better and the price is amazing. Would drop off the wine basket for the holidays if I didn't live on the other side of the country. They also answered all questions throughout the process. I am definitely not a bike builder expert haha.
After extensive research across all possible options, I choose the custom Flume. I opted for the Manitou Mastodon fork and upgraded to the GX drivetrain to get the lowest gearing possible, with the smallest chainring for maximum torque.
I am so pleased with the quality of the frame and the overall product - this bike is a fantastic value and I don't regret the money spent at all. The 27.5 wheels on 65mm rims are perfect size to go up to full 4 inch fat tires or down closer to 3 inch - I've now run the full scale and I love being able to swap out for exactly what I need, summer vs. winter.
I've turned it into all season explorer, ready for everything from local trail riding to multi-day bikepacking. I also added a Thudbuster suspension seatpost, dual sided clip pedals, a Sonder Confucious handlebar and ergo bar ends. With a frame bag and a seat pack I can go just about anywhere any time of year! Borealis also built me a 29" x 45 mm front wheel upon request, so now I'm running a hardtail fat bike mullet!
Lots of fun - so many options - that's what I love about fat bikes. This bike seems to be the perfect and affordable platform for whatever I want to dream up, and so far I've been able to ride much steeper and gnarlier terrain than my full suspension 29" ever did.
FLUME CUSTOM BUILD
You can't find a lighter, better spec'd fat bike for the price than the flume custom build, even without a 20% off sale. Carbon post and bars, full sram, no generic knockoff parts, pick your rim width and tires. Terrene yippee ki yay tires highly recommended for sand. This bike rips with no self-steer weirdness or gyro effect running the light tubes provided.
Be prepared to trim your front brake line if assembling yourself (can be done without bleeding if you are careful, and they give you the fittings to do it). Narrow and soft Borealis brand saddle didn't work for me, but still 5 stars.
Once you go fat you'll never go back....Get one!!!
I opted for the Borealis Flume after getting several recommendations for the brand in an online mountain biking forum. After much research between many of the quality brand fat bikes out there, the Flume fit my needs. I also loved the look of the frame and matte black color option. Quite a light bike for not being a carbon frame and the welds look amazing - so smooth. The bike arrived early and in great shape. I’ve just recently completed the build and am looking forward to its maiden voyage this weekend! I anticipate being thrilled.