Update: Check out my updated Tubeless Fatbike Guide for the non-split tube method. The method shown below is still relevant, and may be more reliable in situations where bead retention is of greatest concern, such as on rough rocky trails. The non-split tube method described in the guide mentioned above is a little lighter. For the most reliable tubeless system, consider adhering the split-tube to the tire bead to create an airtight unit, much like a tubular tire. (2/16/2014)
This is not an official guide to fatbike tubeless set-up. Plenty of resources are available online and depending upon your equipment (tires and rims) and the tools at your disposal (including a compressor), there are multiple approaches. This video is useful, and there is plenty of info to start with on this thread. For use with almost any wheel and tire combination, the “ghetto” tubeless system is preferred for its reliability. In short, a standard tube is cut into a rimstrip with the valve intact. It is laid over the rim, and the tire is mounted over top. The tire is inflated with a compressor to ensure that it “catches” the air. If inflated too slowly, air may seep out from under the bead and the tire will remain limp. Once the tire has seated onto the rim, the valve core is removed and liquid sealant installed to fill any micro-gaps in the system and to line the inside of the tire. Some sealant will remain liquid to fill future punctures– this is the greatest value to me in the prickly southwest. Each wheel lost about a half-pound of weight.
Fatbike tires are variable in dimension– some fit very tight to the rim, and some are loose. To ensure a tight fit, a layer of foam was installed with duct tape to fill the cavity of the Surly Marge Lite rim. I found a $10 sleeping pad at a camping and hunting superstore. Similar product can be sourced from a home improvement center. With the foam in place the tire was challenging to install onto the rim, but it easily held air and could have been inflated with a standard floor pump. A compressor was used.
Pink duct tape was all I could find at the local drug store. Stan’s sealant is preferred. A 24×2.7-3.0″ tube was cut for the rimstrip, although a similarly wide 20″ tube may fit tighter. The rim was drilled for Shraeder valve. Jeff from Two Wheel Drive was invaluable to the success of this project.
The tire is seated. The white foam is window cleaner, used to help the bead slide into place under pressure. Remove the valve core and inject liquid sealant into the tire. Reinstall the core and inflate to pressure. I used about 6 oz. of Stan’s sealant per wheel and inflated the tires to 40psi to ensure that they would roll nice and round.
Carefully trim the excess tube with a blade.
Heavy, but a bit lighter. More importantly, I can safely crawl through the desert without fear of punctures. Each wheel weighs about 7 lbs 12 oz (3.5 kg) with tires, cassette, and rotors. The front hub is a Shimano dynamo hub with a 203mm rotor.
Thanks to Trevor at Surly for the lovely tires– folding 120tpi 26×3.8″ Surly Knards.