Bike Test: Chumba Ursa Major

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Chumba is a different type of bike company because it’s a small builder. When you walk into the offices at 8 a.m. on a Monday morning, you’re likely to find bins of raw metal and tubing rather than cubicles and water-cooler banter. The quality control personnel will be carefully checking over the tubing to be passed off and then mitered for an exact puzzle-piece fit. All of Chumba’s bikes are welded by the company’s highly skilled welders, then carefully aligned using a 360-degree rotating alignment table. Yeah, these guys are perfectionists. As a bonus, this process is entirely done in the United States. Chumba takes a lot of pride in being able to display a made-in-the-USA sticker on its products. These guys are craftsman in every sense of the word. That’s why we decided to bring in Chumba’s newest creation, the Ursa Major, for a full MBA-style test.



The Chumba Ursa Major is built for riders looking for a bike that can hold traction through the loosest of turns. The big tires don’t mind getting a little hang time, and the American-made frame can take quite a beating. This is a versatile fat bike—one that isn’t just built for snow or sand riding. Riders seeking a lively bike will love the geometry of the Ursa Major and trail riders might find themselves enjoying this bike as a great winter training tool. Chumba tested the Ursa Major in varying conditions, such as snow races in Utah, Idaho and Wyoming, and on the dirt trails of Colorado and Texas. The Ursa major is built tough and ready to handle whatever terrain you want to throw at it.


It doesn’t take long to notice the American flag on the seat tube of this beastly bike. Chumba’s Ursa Major sports an American hand-crafted steel frame and stainless steel sliding dropouts. The Ursa Major has an oversized 44-millimeter head tube and a threaded English-style bottom bracket. Chumba used a 197×12-millimeter rear thru-axle to gain a more responsive and laterally stiff feel. The standover height was lowered for all sizes to allow riders to touch the ground, even when standing in the snow.

M2Chumba5Sliding dropouts: These stainless steel sliding dropouts give the Ursa Major the ability to run either 4-inch- or 5-inch-wide tires while keeping the chainstays as short as possible.


The sliding dropouts on the Ursa Major offer riders the ability to run either 4-inch- or 5-inch-wide tires while keeping the chainstays short. The dropouts also allow the option to run this bike as a single-speed. The cockpit displays a Race Face 35-millimeter handlebar that is 760 millimeters wide and a 60-millimeter-long stem. The Rockshox Bluto fork with remote lock out was an upgraded option over the steel fork that would normally come with this bike. The Thomson Elite dropper post is also an upgradeable item over the rigid aluminum Race Face seatpost.


Setting tire pressure: Due to a fat bike’s large-air-volume tires, a small difference in pressure goes a long way. When we tested pressures around 15 psi, the balloon-sized tires bounced us around like a 25-cent machine bouncy ball. We lowered the pressure a little bit at a time and found the ticket for our local trails was between 9 and 11 psi. These low pressures allowed for gobs of traction and small-bump compliance without hindering our climbing efficiency. One of our test riders said that a person buying a fat bike should experiment with tire pressure in order to gain the best ride quality for his or her local trails.

Moving out: After we set the sag to the recommended pressure on the Bluto fork, we took off for the mountains. When we started pedaling around on the Ursa Major, we immediately noticed the wide distance between the pedals. The large Q-factor (wide crank spacing, basically) of the Ursa Major made pedaling feel a little awkward for the first ride, but eventually we adapted to it. We rode the Ursa Major mainly on dirt roads and trails, but Chumba claims this bike is just as good in the snow as it is on the dirt.

M2Chumba4Keep it spinning: The super-small 26 tooth Race Face chainring and the 42-tooth XT 11-speed cassette made it possible for the Ursa Major to climb like a mountain goat. The big traction of the big tires helped out quite a bit as well.

Climbing: The Ursa Major’s hardtail frame and remote fork lockout provided a stiff platform for climbing. The fat tires took the edge off small bumps and provided improved traction. The increased traction allowed our riders to charge up steep, loose sections with little to no tire spin. Towards the beginning of our rides, the Ursa Major climbed fast and strong, but after lugging the large tires around for longer periods of time, we became tired. Our testers appreciated the 26-tooth chainring that allowed them to crawl up the steepest sections with just a little bit of grunt.

M2Cumba12Float over the sand: The Chumba climbs up sandy trails like a champ. Let the fat tires grab hold and send you on your way.

Cornering: When it came time to corner, body language became oh-so important. We had to throw our weight hard into the corners to brake the strong gyro effect of the massive wheels. After we adjusted our riding style a bit, the Ursa Major could shred corners faster than we expected. The large footprint of the tires held traction well, and the wide handlebars allowed us to lean the bike as far as we wanted to. The Ursa Major favors wide-open turns and isn’t afraid to plow through the loose blown-out sections.

Chumba-FullThe Great Bear: Chumba named their new fat bike after the star constellation Ursa Major, which translates to “The Great Bear.” This bike was appropriately named. It rides a little like a grizzly bear, ready to “maul” whatever trail is in front of it.

Descending: When we pointed the Ursa Major downhill, we quickly noticed this bike was comfortable with higher rates of speed. The Ursa Major’s relaxed head tube angle and huge ground-biting tires offered our testers a confident feeling when rushing down the mountain in a hurry. The Ursa Major’s added grip gave us loads of confidence to stay off the brakes longer as we plunged down the trails. The fat tires absorbed a lot of the vibrations, but when it came to bigger hits the Bluto fork punched in its time card and went to work.

M2Chumba8Optional upgrade: The Ursa Major comes with a steel fork, but Chumba will swap it for an additional fee to a RockShox Bluto. This upgrade is a must for aggressive trail riders.

M2Chumba14Crank the speed up: The Ursa Major holds traction well, allowing riders to feel confident when charging down the trails at full force.

Braking: In order for our test riders to feel confident hitting blistering speeds on wide-open sections of trail, they needed to trust that the bike was capable of safely slowing the fat tires down. Chumba made braking power a top priority by utilizing Shimano’s XT brakes. We felt the XT brakes with 180-millimeter rotors offered a solid amount of power that allowed us to breathe easy while traveling down the trail. When we grabbed the brakes, the tires held traction well and didn’t skid unless the rider really put some muscle into the levers. The Ursa Major’s traction made for a fun day when we could remind ourselves to ride it, not slide it.

M2Chumba13Who said fatties can’t jump? At times the Ursa Major confused itself with a trailbike. Lay off the brakes and let the big tires soar.


Tire pressure is key for getting the best ride quality out of your fat bike. We recommend purchasing a good tire pressure gauge that can read lower pressures accurately. Chumba offers the Ursa Major with many different upgradeable options. Riders looking to use the Chumba as a trail bike will most likely appreciate the upgrades to a suspension fork and dropper post. Winter time riders looking for a snow or mud bike might think about getting the steel fork and possibly the single-speed drivetrain to improve durability by using fewer moving parts. Chumba also offers a full line of gear bags for those riders looking to do longer adventure rides with their Ursa Major.



Riders in the market for a do-it-all fat bike should look to the Chumba Ursa Major. It’s proficient on trails as well as in the snow and offers a fun and playful geometry. Chumba’s Ursa Major can tackle your favorite local trails or take you on your next adventure. Pick a place during any season of the year and the Ursa major will take you there with confidence. Chumba sells its complete bikes and frames through their website, making it easy for riders to take a Chumba on their next trip. We still don’t recommend a fat bike as a first bike; however, if you are considering a “fatty” as your next bike, make sure to put Chumba’s Ursa Major on your short list. The bike is surprisingly nimble, impeccably well-built and flat- out fun to ride.


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