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)
My tubeless Pugsley has been a blessing in the land of cacti and goatheads– no pinches, punctures, or burping. Burping is modernspeak for a tubeless tire rolling away from the rim, momentarily, losing a little pressure and sealant. Two Surly Moonlanders are rolling out of Two Wheel Drive this week here in Albuquerque, NM. Their owners will never know the annoyance of slow leaks in 4.8″ tires, nor the weight of supersized tubes. Even in temperate zones without thorns, tubeless fatbike wheels are the way to. Surely, it is the cheapest way to lose almost a full pound on the bike, especially out of the wheels.
Over the past few weeks, Two Wheel Drive has become the premiere fatbike shop in Albuquerque, perhaps even the entire state. Out the door– two Moonlanders this week, a white Pugsley last month, and a Neck Romancer Pugsley in the next month. Jeff and I are well versed in tubeless systems for wide rims and tires, and I can heartily attest that these bikes are for much more than riding on snow. Here’s what we have learned in converting six fat wheels to tubeless:
All fatbike rims have deep rim channels, and most fatbike tires fit loosely which means that any air injected into the tire will escape from under the bead. The solution is to build up the rim bed for a tighter fit. My solution is to use thin foam, a strip of duct tape, and then a rubber rimstrip made from a repurposed tube. Twenty inch (20″) tubes work best on 26″ fatbike rims, as the tube fits tight to the rim and makes tire mounting easier. Look for 20×2.75-3.0″ tubes; 24×2.75-3.0″ tubes also work. It is necessary to use a Presta valve with a removable core (Q-tubes, from QBP are all removable cores), or a standard Schraeder valve which all have removable cores.
Our first effort used a narrow foam strip. The tire mounted onto the rim easily and nearly seated with air from the compressor. Still, it remained limp. Try again.
A second time, with a wider strip of foam. For reference, we cut the foam about the same width as the cutouts in the rim.
A layer of duct tape secures the foam, and adds a little bulk near the edge of the foam to ensure a tight fit when seating the tire. The foam used was a cheap camping pad from Sports Authority, about 5-8mm thick. We have also used foam pipe insulation front the hardware store. Punch a hole for the valve.
Cut a 20×2.75-3.0″ tube along the outside seam, opposite the valve, to create the airtight rimstrip. It may be possible to do a tubeless fatbike system without the rubber rimstrip, but Jeff and I reckon this method is less likely to burp and the tire is less likely to “walk” along the rim at low pressures. Our system is refined, but not yet perfect. We strive to develop a simple, replicable system of cheap lightweight parts.
This Moonlander receives some more aggressive tires. A Lou replaces the Big Fat Larry in back, and a Bud will do the steering up front. All tires are 4.7-4.8″, but the Bud and Lou borrow a taller, more aggressive tread from the Nate.
Fit the tire over both sides of the rim to start. Pull one bead up and over the rim, taking care to keep the rubber rimstrip between the tire and the rim. This will ultimately provide a tight seal and an airtight junction. Try to do all of this by hand, to avoid pinching a hole in the tube. If necessary to use a tire lever, pull the damaged rimstrip outward so that it will eventually be trimmed away.
Both sides mounted, inflated. Remove the valve core, deflate, inject about 6 oz. of Stan’s sealant through the valve. Re-install core, inflate, shake the wheel to allow sealant to contact all internal surfaces.
Trim the excess rubber for a clean look, and to shed some grams.
Lou– fat and mean.
The giant cardboard box in which “Lou” arrived will be the basis for a Halloween costume ten months from now. Painted yellow with a cylindrical yellow dot on top, Jeff plans to be the Lego Man next Hallow’s Eve.