Most FatBike rims on the road today are either 80mm or 100mm wide, the former usually set up with 4″ wide tires, the later with 5″ tires. There are however many exceptions.
65mm Surly Marge rims have morphed from their double wall with canti rim braking surface days into single wall disc only rims that are drilled out to be even lighter. There are other widths available now that fit somewhere in between 65mm and 100mm, like the 70mm Whisky Carbon No. 9’s pictured above. There are a number of drilled out vs. solid rim options in a variety of colours, some made specifically for offset dishing while many others are made with a symmetrical bike frame in mind. Most FatBike rims are aluminum, but a few are now carbon.
The biggest two questions when it comes to rim width (after you make sure the rims you’re considering will actually work in your frame and fork) are how much resulting tire width you’re looking for, and the weight you’re targeting.
Weight is pretty straight forward. Generally narrow rims are lighter, though wider drilled out rims can have surprisingly low relative weights and carbon is unquestionably light at any width.
Resulting tire width isn’t quite as straightforward because different width rims will affect how the same tire ‘sits’, such that a narrower rim creates a rounder tire whereas a wider rim creates a boxier tire. Generally speaking a boxier tire creates more surface rubber rolling along the ground, so the same tire with a wider rim can affectively feel like a wider tire.
It’s important to note that tires have different cornering characteristics when sitting on different width rims, and we can tell you how a particular set up can affect cornering. Generally though any 80mm to 100mm rim can with any 4″ to 5″ tire (again, assuming your frame and fork can accommodate the set up you’re thinking of). If you’re looking at dimensions outside of those ranges be sure to talk to use first so we can make sure you’ll be happy with the ride.