TIL #2 – Fatbike Rim Width

Fatbike Rim Width

Conversation about tire choice can include multiple directions of thought.  Discussion today quickly focuses on the affect of rim width to a given tire.  You may have read about or experienced for yourself the push for a wider rim on today’s road bikes, which allow for a stiffer wheel and also have an impact on aerodynamics in a positive way.  Well, what happens when you take a fat bike and essentially cut the rim in half?

Surly Rabbit Hole 50mm (top) and Specialized Fatboy 90mm (bottom)

First big difference was a change in rotational mass of the wheel.  Each rim, being around 250g lighter than the wider, 90mm stock option, ended up dropping over 1lb of rotation mass, a significant amount of weight to not make go in a circle for hours at a time might I add.  This was one of the main goals of the rim swap for this project, but equally important, was a what this narrower rim did to the profile of the mounted tire.

Tire mounted to 90mm wide rim; notice how wide the tire casing is compared to the side knob.

Tire mounted to 50mm wide rim; notice the widest portion of the tire is the side knob.

Changing the tire profile so that the side knob is clearly the outer most portion of the tire will change how the bike handles in corners and also call for a change in tire pressure.  Actual feedback from the rider is the drop in rotational weight was noticeable, especially when accelerating.  However, the change in tire profile will take a bit of getting used to.

Our thoughts on making drastic changes to your rim width, specifically on your fat bike, are go narrow for a faster wheel system during spring, summer, & fall.  Come winter, the wide rim helps support the tire better when ripping through fresh powder at 2psi.

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