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New Arctodus fat bike from Otso Cycles devours the biggest tires, keeps q-factor in check

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It’s now been six years since Otso Cycles spun out of Wolf Tooth Components, introducing the Voytek fat bike to the world in the process. In our opinion, that Voytek is still one of the best fat bikes you can buy, but it hasn’t stopped Otso from thinking about what comes next. From one legendary bear to another, the Arctodus gets its name from the Ice Age monster that was supposedly the largest bear to ever walk the earth.

That’s fitting since the Actodus fat bike is meant to roll the biggest fat bike tires currently available…

Otso Cycles Arctodus fat bike in snow
All photos c. Otso Cycles

Starting with a chromoly steel frame, it’s clear that the Arctodus is built for slightly different adventures than the carbon fiber Voytek. Designed specifically for maximum stability & flotation with backcountry-worthy durability, the Actodus is meant to stand alongside the Voytek – not replace it.

Otso Cycles Arctodus tuning chip dropouts

It’s no big surprise that the frame continues the use of Otso’s excellent Tuning Chip dropout system. Given the wide variety of tire and wheel sizes the Arctodus is built for, the ability to adjust the wheel base by 20mm, BB height by 4mm, and the head tube angle by +/-0.5º will be a welcomed touch.

Otso Cycles Arctodus head tube

Otso Cycles Arctodus geometry


Up front, the Arctodus is suspension corrected for a 120mm fork with a 68.5º head tube angle and 485mm axle to crown. Want it slacker or steeper? The head tube is designed to work with the Wolf Tooth GeoShift Angle Headsets which can change the head tube angle by +/- 1º or 2º, allowing for head tube angles from 66.5º to 70.5º.

The Arctodus will be sold in four frame sizes from small to extra large.

Otso Cycles Arctodus fat bike tire clearance

Tire Clearance

In terms of tire clearance, the Actodus was built around a 26 x 4.8″ tire for optimal handling. However, the frame and fork will swallow a 26 x 5.05″ or 27.5 x 4.5″ tire with ease. Actually, the frame will clear up to a 26 x 5.25″ tire and the fork will clear up to a 26 x 5.4″ tire on 100mm rims – though tires that wide don’t actually exist (yet?). It’s important to note that the Arctodus frame offers the same clearance in all Tuning Chip Positions, not just at the back.

Otso Cycles Arctodus 1x12 drivetrain clearance with tire

Yes, there are other frames on the market that will clear tires that wide but Otso claims this is the only frame on the market that will allow for the use of a 12-speed drivetrain without any chain interference with the tire.

Otso Cycles Arctodus narrow Q factor bb

Narrow(er) q-factor

More impressive is that Otso was able to accomplish this while keeping the q-factor relatively narrow with a 100mm BSA bottom bracket. It’s not Voytek-narrow, but at 205mm with a RaceFace Aeffect crankset, it’s impressively compact considering the tire clearance, drivetrain clearance, and 36t round chainring clearance.

Otso Cycles Arctodus offset rear hub

How did they do it? It all centers around a 197 x 12mm rear hub that is offset to the driveside by 5mm. That places the cassette farther out from the tire, and allows for the chain/tire clearance.

Otso Cycles Arctodus fat bike blue


The Arctodus is dropper post compatible with a cable port in the seat tube, and runs full external housing for brakes and derailleurs. You’ll find three-pack mounts on the inside of the downtube, and on both fork lets, plus standard bottle cage mounts on the seat tube and the bottom of the downtube. There are also rear rack mounts for the frame.

Otso Cycles Arctodus black

Pricing & Availability

Available now in Glacier Blue & Purple, or Black & Silver, complete base builds start at $2,590 with Shimano SLX 1×12 and the frameset will be offered for $1,390. As usual, the components are all customizable through the Otso Custom Bike Builder.


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1 year ago

Why don’t fat bike manufacturers join the slack head angle club…I don’t get it

1 year ago
Reply to  Mtnfun

Fatbikes are designed for winter riding as well as sand or other soft materials. If the bikes were slacker, in general they would handle worse. A 4.6″ tire is intrinsically slow and handles more lethargically.

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