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Ships within 48 hours · Estimated delivery Jul 4 - Jul 9
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Description
fat e bike cube ELECTRIC FAT TIRE E-BIKEIntroducing the all new Keystone Electric Fat Tire Bike. Since 2013, Borealis has specialized in lightweight, high end fat bikes. The Keystone is our first ever Class I electric bike. The frame geometry is optimized for riding just about anything with clearance for up to 5 wide tires. Paired with the most technically advanced components in the industry, the Keystone sets the standard for premium quality Electric fat bikes. HIGHLIGHTS Color: Gunmetal
Introducing the all-new Keystone Electric Fat Tire Bike. Since 2013, Borealis has specialized in lightweight, high end fat bikes. The Keystone is our first ever Class I electric bike. The frame geometry is optimized for riding just about anything with clearance for up to 5” wide tires. Paired with the most technically advanced components in the industry, the Keystone sets the standard for premium quality Electric fat bikes.
HIGHLIGHTS
- Color: Gunmetal Grey with Cobalt Blue Graphics
- Weight: 56 lbs. as shown.
- Standard features include Shimano EP8 Drive Unit, Shimano 630Wh Battery, SRAM G2 RS brakes, Mastodon Pro EXT 120mm suspension fork, carbon handlebars, dropper 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”.
- Lightweight, 6000 series aluminum frame comes with internally routed cables, 1-2 bottle cage mounts and lizard skin protection.
- Keystone Frames are backed by our LIMITED LIFETIME WARRANTY.
ASSEMBLY
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 kit will be included with your order that has all the necessary tools assemble your bike, including a multi-tool, torque wrench, and shock pump. If you are not familiar with this level of assembly, we recommend having your local bike shop complete the assembly.
Stay tuned for our step-by-step assembly video.
WHEELS AND 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.
- Tubes must be removed and tubeless valves installed for tubeless set up. We recommended to have this completed by a professional bicycle mechanic.
SIZE CHART
BUILD SPECS
| Frame | Borealis Keystone Aluminum 15", 17", 19", 21" |
| Drive Unit | Shimano DU-EP800 |
| Battery | Shimano BT-E8036 (630Wh) |
| Display | Shimano SC-EM800 |
| Assist Switch | Shimano SW-EM800L |
| Speed Sensor | Shimano EWSS300L540A |
| Fork | Manitou Mastodon PRO EXT 120mm, 51mm offset |
| Headset | FSA w/ Star Nut |
| Stem | Borealis 50mm |
| Handlebar | Borealis Carbon |
| Grips | Ergon GP1 |
| Saddle | WTB Volt Medium Steel |
| Seat Collar | Borealis Bolt-On |
| Seatpost | KS Lev Integra 125mm (SM, MD) / 150mm (LG, XL) |
| Brakes | SRAM G2 RS |
| Rotors | SRAM HS2 200mm front / 180mm rear |
| Shifter | SRAM AXS Pod Contoller Right Bridge w/ MMX Clamp for GX Eagle Transmission |
| Derailleur | SRAM GX Eagle Transmission Derailleur |
| Cassette | SRAM GX Eagle Transmission Cassette 10-52T |
| Chain | SRAM GX Eagle Transmission Flattop Chain |
| Crank Arms | Samox 170mm |
| Chainring Mount | Samox 104 BCD for 75mm chainline |
| Chainring | SRAM Eagle Transmission E-Bike MTB Chainring 104 BCD 36T Steel |
| Rims | Your choice of SunRingle Mulefüt SL - 26x80, 27.5x80, or 27.5x65 |
| Spokes | Straight Gauge 2.0 Black |
| Hubs | Borealis Gen 4 15x150 / 12x197 |
| Tires | Your choice. All tire options are listed online. |
| Included | Shimano ECE80042 Battery Charger, AXS Power Pack, Kickstand, UDH Hanger, Key for battery release, Borealis Rear Thru Axle, Remote Battery Charging Adapter |
| Weight | Size Medium w/ Mulefut 27.5x80 & Terrene Yippee Ki Yay 4.3" Tires: 56 lbs. |
FRAME SPECS
| 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 | 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 | Shimano EP8 |
| Crankset (Max Ring) | Chainline 75mm / 1x (38t) |
| Rear Brake (Rotor) | 74mm post (160–180mm) |
| Rear Spacing | 197 x 12mm thru-axle |
| Rear Axle | ø12 x 222L, TP= 1.0, TL = 16 |
| Derailleur Hanger | SRAM UDH |
| Bottle Mount | Small & Medium: 1 (downtube) / Large & XL: 2 (downtube & seatube) |
| Rear Rack Reccomendation | Old Man Mountain Divide Fat |
| Rear Rack Mounts, Upper | Yes |
| Axle to Crown | 531mm |
| Steerer Tube Size | 28.6mm |
| Steerer Style | Tapered |
| Crown Seat Diameter | 40mm |
GEOMETRY CHART
| Small 15" | Medium 17" | Large 19" | X-Large 21" | |
| Effective Top Tube | 630 | 645 | 660 | 665 |
| Seat Tube Center to Top | 381 | 432 | 482 | 533 |
| Head Tube Length | 160 | 160 | 175 | 190 |
| Head Tube Angle | 69° | 69° | 69° | 69° |
| Seat Tube Angle | 73° | 73° | 73° | 73° |
| Chainstay Length | 480 | 480 | 480 | 480 |
| BB Drop | 60 | 60 | 60 | 60 |
| Reach | 420 | 435 | 445 | 446 |
| Stack | 688 | 688 | 702 | 716 |
| Standover Height | varies based on wheel and tire size | |||
| Wheelbase | 1187 | 1207 | 1223 | 1229 |
| Fork Offset | 51 | 51 | 51 | 51 |
FAQ:
| Can I use the Keystone in cold temperatures? | It is okay to use your Keystone in the operating temperature range, suggest by Shimano: -10 - 50°C |
| How do I remove the battery? | Each Keystone will come with a set of keys. Make sure to save your spare key and safe location. Insert the key fully into the lock cylinder on the non drive side of the downtube until it stops. Rotate the key clockwise until the battery drops from the downtube providing access to the latch release mechanism. Use your index finger to gently depress the spring which will fully release the battery. Use caution to support the battery when removing it so it does not fall to the ground. |
| How can I file a warranty claim for the drive unit and other electronic components? | Contact an authorized Shimano STEPS dealer. |
| Can I change my motor/power settings? | Yes, you can customize your motor settings via the app as well as update the firmware. You'll need to download the Shimano E-tube mobile app. |
| Can I change the max speed? | No. Depending on where you've purchased your Keystone it will either have a max assist speed of 20mph or 25km/h. This setting cannot be modified by the user or a dealer. |
| Can I purchase an extra battery? | Yes, you can purchase a spare battery kit with a spare downtube cover directly from Borealis. Spare battery kits may not be available in all markets. You can also purchase a spare battery from Shimano, but it will not include a battery cover. |
| Can I ride the Keystone without the battery? | No. This will void your warranty with Shimano and cause damage to the motor system. |
| Do I need to update the firmware / software? | Firmware can be updated via the Shimano E-tube mobile app. |
| How do I use walk mode? | Hold the upper button (down assistance level) for 1 second until the display turns blue and displays WALK mode. Press and hold the same button to power the rear wheel. |
| How long does it take to charge the Shimano 630Wh Battery? | With the included EC-E8004 charger, the battery can fully charge in 6 hours. |
| How long will my battery last? | The remaining battery capacity is affected by temperature and cycle count. Generally, it decreases approximately 5% a year. This means roughly 95% capacity remains after 1 year, and 90% after 2 years. |
| How should I store my bike and or battery? | Charge your battery to approximately 70% before storing for long periods of time. Store in a cool, indoor location with a stable temperature between approximately 10 - 20 C / 50 - 70 F. No direct exposure to sunlight or rain. |
| Are the electronic components waterproof? | Yes, the STEPS system is waterproof as long as all components of the system, including the battery and battery cover, are installed correctly. We recommend not using a high-pressure washer to clean your Repeater, but riding in the rain and regular cleaning are okay. |
| My bike won't turn on, what do I do? | First, make sure all cables are plugged in, if they are then try removing and reinstalling the battery. If it still won't turn on try charging your bike for a few hours. If your bike is too hot or too cold, it might not turn on. If your bike still does not turn on, contact a Transition or Shimano dealer for support. |
| Should I only charge my battery when it's completely drained? | No, simply charge the battery any time you need it, frequent charges actually help battery longevity. Avoid letting the battery discharge completely. Charge to 70% before storing for long periods. |
| What are the different error codes and what do they mean? | Whenever you encounter an error code, first cycle the power off and then back on. If the code persists, remove the battery and then reinstall, which will hard reset the system. If neither of these steps resolves the issue, please reference the Shimano error code list. If you cannot resolve your error code via your Etube mobile app please visit your nearest Shimano STEPS dealer or contact Shimano STEPS customer support. |
| What is the range and how can I maximize it? | There are many factors that affect battery range, such as, how much effort the rider is providing, the gradient of terrain, ambient temperature, and rider weight. The best way to maximize your range it to spend more time in Eco and Trail modes, and minimize the amount of time spent in Boost mode. |
| What is the widest tire the Keystone can fit? | 26x5.0" or 27.5x4.5" |
| What kind of maintenance is needed on the drive unit and how often? | The drive unit is sealed and cannot be serviced. If there are any issues with the drive unit, it will need to be removed and sent back to Shimano for service or replacement. The drive unit along with the battery is designed to last over 1000 charge cycles. Assuming you're getting 30 miles (48Km) per charge, the drive unit should last 30,000 miles, or much longer than pretty much any other part on your bike. |
| Why does my bike stop giving assistance over a certain speed? | Depending on where you've purchased your Keystone it will either have a max assist speed of 20mph or 25km/h. This setting cannot be modified by the user or a dealer. |
| Will environmental temperature affect battery life? | The battery life will be shorter during cold temperatures, this is not a sign of a problem. |
| Will my bike be delivered with a charged battery? | Your Keystone was shipped in a "sleep" mode with the battery at approximately 30% charge. It is recommended to fully charge your battery before the first ride. |
Shipping Notes
- Free Standard Shipping on $100+ Orders to the USA.
- Except Preorder products are shipped in 48 hours.
- Delivery to the USA:
- Standard Shipping : 3-10 business days
- If time is of the essence, please consider selecting expedited delivery for faster service.
Exchange/Return Notes
- We offer a 30-day return/exchange service after receiving.
- Final sale items are not eligible for returns or exchanges.
- To process your return/exchange, please contact us at [email protected]
- Please click here for more details>>> Return & Exchange Policy
4.8 ★★★★★
Based on 165 reviews
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Product Reviews
★★★★★ 5
Great product AND customer service!
Color: Black Full Mesh, Style: Executive
I'm having a hard time writing this review because I can't tell which one I like better: the product or the customer service!
I work on a computer all day, so a comfortable office chair is critical for me. This chair is great - it's adjustable in every way I need it to be, especially the armrests. The breathable mesh is both durable and supportive, and is more comfortable to sit in than the "overstuffed" chair it replaced.
Let me just say: no company provides better customer service than MOLENTS. Right after assembling my chair (which was very easy, btw), I registered for the 2 year warranty they offer. The NEXT DAY I received an email from Alice in their customer service department 1) to confirm my warranty, 2) to tell me about the free foam seat cover they were sending me, and 3) to make sure the chair was comfortable and easy to assemble. Very few companies take the effort to follow up with customers right after making a purchase like that.
I'm extremely happy with this purchase. This chair is worth MORE than it's weight in gold, and I strongly recommend to anyone thinking about buying an office chair to buy it from MOLENTS - you won't regret it.
Oh, and if Alice's supervisors are reading this: she absolutely deserves a promotion!
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Reviewed in the United States on March 13, 2026
★★★★★ 5
Great value and a good chair
Color: Black Full Mesh, Style: Executive
Great chair for the price. Not as solid as an Ergo but it's not thousands of dollars either. It's pretty easy to assemble and the directions are good. It rolls well on LVP flooring and they offer 'upgraded' wheels at no cost from what I can tell. I didn't order them since the included ones work perfectly.
I'm 6'4" and both the seat and arm heights can be adjusted to fit me well. The mesh seat is comfortable and the back works fine. The only downside for me is that the lumbar support doesn't adjust quite high enough to actually reach my lumbar area, but I think it would work for most folks.
Overall it's hard to argue with the cost and even if it only lasts a few years it's worth the money.
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Reviewed in the United States on December 21, 2025
★★★★★ 5
Great Chair and Outstanding Customer Service
Color: Black Full Mesh, Style: Executive
I desperately needed a new office chair. I ordered this chair with the mesh seat and it spike up my sciatica. I reached out to the company and Alice took great care to address the issue. She sent me a new seat with a foam cushion and it resolved the issue immediately. The chair is incredibly comfortable with the lumbar support, adjustability and foot support. She also sent me upgraded wheels as my chair is on a thin chair mat on hard wood floors. Alice was extremely responsive with possible options and very thorough with instructions on how to replace the seat. It is a high quality chair that I anticipate will last me quite some time. I highly recommend this company and will definitely order products from them again should the need arise. Thank you, Alice!!
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Reviewed in the United States on June 10, 2026
★★★★★ 5
Well-packaged, quality materials, easy to assemble, very comfortable, great customer service
Color: Black Full Mesh, Style: Executive
When I received this package, I was surprised at how small/compact it was--hard to believe a high-back office chair could fit in that box! As I unpacked it, I was impressed by two things: first, how incredibly well it was packaged with an obvious intent to protect the components; second, how solid, heavy-duty, and high-quality those components were.
I got the box unpacked and read the instructions. They were simple and easy to understand, and included so many "here's a good tip" notes that it was obvious that a lot of thought and experience had gone into writing them. I found the chair simple to assemble and had it done in less than 15 minutes.
The chair was very adjustable. I was able to get the height to exactly what I wanted with no trouble at all. I was also able to adjust the height of the lumbar support, and to adjust how far it extended. There are a lot of adjustments you can make, the instructions lay that out quite thoroughly, too. As a result, the chair was very comfortable and helped me sit with a healthy posture.
I bought this chair because I had begun having an ache in my lower back, which I suspected was due to a chair I had been using for over 5 years. Within 3 days, the back pain was gone.
I was also very impressed with the customer service. Their manual mentions in multiple places things you can try if you have any issues, and always ends with "call us". Their team reached out to me after a few days to make sure I got the chair assembled with no issues and that it was comfortable. This was all part of the all-around quality of this purchase.
I'm very happy with this chair!
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Reviewed in the United States on June 5, 2026
★★★★★ 5
Comparable to Higher-End Chairs, Solid Build and Support Without the Premium Price
Color: Black Full Mesh, Style: Executive, Color: Black Full Mesh, Style: Executive
I’ve been using this chair for a bit now and it’s been a genuinely upgrade. The build quality stands out right away, it has real heft and doesn’t feel cheap or hollow. Everything fits together cleanly and once assembled it feels stable and planted. I’m over 6 ft and 200+ lbs and it handles that without any issue, no creaking or sense that it’s being pushed to its limits.
There’s enough space in the seat and back that you don’t feel boxed in. I added an extra ergonomic cushion and it still feels roomy, which isn’t always the case with chairs in this category. The adjustability helps a lot here, especially the lumbar support. Being able to move it up and down and also forward and back makes it easy to actually get it where you need it, instead of just accepting a fixed position. The armrests are also easy to dial in, especially if you’re switching between typing, reading, or leaning back a bit. The tilt range is useful, and the tilt tension is stronger than I expected. Even at my size it takes a bit of effort to lean back, which I see as a positive since it feels controlled and supportive rather than loose or overly easy to recline. The mesh is another strong point. It came in perfect condition, no snags, no loose threads, no rough edges anywhere. There weren’t any bits of untrimmed plastic on the frame either, which says a lot about the quality control. The mesh itself is taut with a bit of bounce, so it doesn’t sag but still has some give, which makes long sitting sessions more comfortable.
Assembly was straightforward and clearly thought through. The instructions are easy to follow, but what stood out were the built in redundancies that keep you from second guessing anything. There are multiple left and right indicators when installing the arms, a clear front facing marker for the gas lift, and the screws are labeled in the packaging so you’re not guessing which goes where. It’s one of the smoother assembly experiences I’ve had.
I also reached out to activate my warranty and had a very positive experience. I spoke with Alice who was very knowledgeable, quick, warm, and they went out of their way to help me with whatever I needed. When I inquired about the extra screw holes under the chair, she let me know that this was for a foot rest which was still in the production phase and unprompted offered to have one shipped to me when they were ready! There is an excellent team behind the product.
Overall: well built chair with good materials, thoughtful design choices, and good adjustability to make it work for different setups. It feels durable, comfortable over longer periods, and especially well suited if you need something that can handle a larger frame without sacrificing support.
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Reviewed in the United States on April 20, 2026
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