If you have a single wall fatbike rim (eg: SunRingle Mulefüt, PUB Carbon, HED., Specialized Fatboy OE, DT Swiss BR 2250 Classic, etc), you should be using a spacer between the rim wall and valve nut when setting the wheels up tubeless. If not, it’s likely you’ll eventually have problems with leaks around the valves. And these sure aren’t fun when they crop up on a cold day out in the woods.
The diagram above shows why: Tubeless valves don’t work well with single wall rims: the base of the valve ends up poking through the rim wall, so when the nut is tightened down, instead of sealing the gasket against the wall, it bottoms out leaving the gasket loose. Sometimes there’s a visible gap, other times it’s just looser than it should be, and it will eventually leak.
Sometimes it’s possible that sealant will build up in the gap and keep the leak at bay for a while, but as the valve gets bumped, the weather turns cold and things contract and harden, leaks will tend to appear.
So what’s the Fix? Fit a spacer between the rim and Presta nut, then tighten up everything snugly. Doing this ensures the gasket can squeeze through the rim, the nut doesn’t bottom out on the base, and everything gets good and tight. (Protip: Press on the valve gasket from the inside of the rim with your thumb while tightening the nut with your fingers. Then when you release pressure on the gasket the nut will end up tighter than you can do with just your fingers. Reversing this process allows the valve to be removed without tools.)
I’ve used a variety of spacers for this, but the most readily available is McMaster-Carr part 90176A155: Nylon Unthreaded Spacers, 1/2″ OD, 1/4″ Long, Black with 25 pieces available for ~$5 (plus shipping). Lowes, Ace, Home Depot, and Menards will all typically have similar spaces in their small-parts sections.
There’s also the Problem Solvers Super P-Nuts which are a replacement Presta nut that has a flared, stepped base, but at ~$7.99 for two I’ll recommend using spacers. (EDIT: Looks like it’s $15.99 for two brass valves and two Super P-Nuts. That’s much better, as a pair of valves typically retails for close to that.)
Even on valves with flat bases this is often a problem because single wall rims tend to be thinner than the unthreaded base of the valves, and this pokes through the rim wall and the nut bottoms out on it. Many of these valves come with O rings to be fitted on the outside of the rim as protection, but this doesn’t solve the issue either as the O ring isn’t thick enough to serve as a spacer.
See the photos below for examples of the issue and photos of spacers used to solve the problem.
(Note: I wrote about this years ago as SUNringlé MüleFüt Leaky Valve Stem Fix, but it was time for an updated post with more details and fresh photos.)
