The Monkey Lab: Rohloff-Equipped Carver Full Suspension Fat Bike

This fat bike was built by Carver Bikes for one of our customers in Marin, CA. He was looking for a new bike that offered the ultimate in plushness and traction. Having ridden Rohloff-equipped full suspension 26" and 29" wheeled bikes for many years, he figured a full-suspension fat bike would be even better, but finding a bike that met this description proved to be challenging. We've seen an increase in fat bike wheel builds over the past few years as these ultra-wide-tire bikes have transitioned from being used only as snow bikes to year-round trail bikes. These bikes have almost all been rigid, as suspension fork availability has not followed the increase in popularity.

There are currently no cross country forks available in the US that offer the needed tire clearance. People have built one-offs with the now out-of-production Maverick SC32 fork or the also out-of-production aluminum Cannondale Lefty forks with removable crowns. The one in-production option, the German:A Flame Wide fork (or the custom version made for Sandman), are not currently available in the US. As a result of a lack of suspension fork availability, frame builders have not brought any suspension frames to market. So, Carver Bikes to the rescue!

After a long search for someone to build a full-suspension fat bike, the customer found Carver Bikes in Maine, who are willing to build just about anything one can dream up. They decided to build the bike around a Risse Racing Trixxy downhill fork, which had the tire clearance for the wide tires and was modified to 100mm/4" of travel to prevent the tire from scraping the crown at bottom out. After several revisions and a long wait, the bike finally became a reality.

The frame is nearly all titanium, save for the bearings and pivot hardware. It uses a 4-bar suspension system similar to what is used by Specialized, Ellsworth, Titus, etc. The non-drive side dropout is Rohloff-specific as is the cable routing. Tire clearance is built around the 3.8" wide Surly Nate model with a 135mm spaced symmetric rear end for the Rohloff SPEEDHUB 500/14. The wide chain line of the SPEEDHUB 500/14 allows for a symmetric rear end, which maintains the dish-less wheel build that the hubs normally offer.

The Rohloff SPEEDHUB 500/14 offers a great drivetrain choice for fat bikes, whether used on snow, sand, or trail. All the gear changing components are housed in the rear hub with an oil bath that keeps the gears and bearings well lubricated and cannot get packed up with snow or mud. Since the chain never moves from the single front and rear sprockets, it cannot fall off during a shift. The shifting mechanism also won't freeze in the extremely cold temperatures that snow bikes see, though a thinner cleaning/hub oil mixture is recommended to maintain consistent shifting. In addition, an internal gear hub allows the rider to change gears without pedaling, which enables a rider to get started again after stalling out. The ability to shift after getting bogged down in the sand was the inspiration for Mr. Rohloff to design the SPEEDHUB 500/14 over a decade ago. These features make the SPEEDHUB 500/14 an ideal setup for the unique terrain and riding applications that fat bikes can handle.

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