Tubeless Tires: Minimum Pressure?

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My MTB uses tubeless tires in 27.5" x 2.2 or so. They've worked well for several years. I've gone back and forth between gravel tires like the Maxxis Rambler, and knobbies like the Minion DHF/DHR, depending on the ride. Finally I got tired of swapping tires so I found one all-around tire, the Maxxis Ardent Race. It's a compromise that is lighter & faster than the Minions, but more robust than the Ramblers.

The Ardent Race has smaller knobs than the Minions and it makes a difference: they sometimes slip where the Minions would grip. I tried using even lower pressures to compensate for this, and it helped. I ran the Minions at 30 rear / 28 front, and got the Ardent Race as low as 25 rear / 22 front. It seems like a small change but it did increase traction.

HOWEVER, the rear tire went completely flat over a few days in storage in my garage. No puncture, but the tire bead unsealed from the rim in a couple spots. Still seated, but unsealed with a couple of slow pinhole leaks. I added a bit more fluid and pumped it back up, it re-sealed and held pressure. So what happened is, the low pressure wasn't sufficient to keep the tire bead sealed against the rim. So I started pumping it up to 40 PSI for storage, then dropping the tire pressures to whatever I need for a ride. This works and it holds pressure.

Has anyone else noticed that tubeless tires need some minimum pressure to maintain their seal?
 
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MRC01

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That's a useful chart, but it doesn't mention the issue here, which is minimum pressure needed for a tubeless tire to maintain its seal. That chart implies that pressures below 20 PSI are OK, but in my experience low pressures like that may work during a ride but the tire will lose its seal with the rim.

PS: I also read their page on why tubeless leaks. They do capture the common issues, but none of them apply to the situation I observed.
 
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In my experience, I've found it is tire/rim dependent on really low pressures and then the added element of rider weight and the terrain you ride on. I"m east coast rock garden lover and like to hammer. I'm running a Fox 34 on one bike with 29r tires and a Fox 36 on another with 27.5's. Both have carbon wheelsets. Very different pressures required to ensure I'm not bottoming out on my rim.

Charts are a starting point IMHO. The best part of tubeless is the customization. The part that SUX is the time required to dial it into your style and terrain.

I started tubeless in my road bike (Trek Domane SLR) and did not see the same benefits as MTB so I'm running tubes in 2 wheelsets on that bike. Different animal for MTB.
 

MRC01

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@BISCUT have you encountered tubeless pressures too low to maintain the seal?

... I started tubeless in my road bike (Trek Domane SLR) and did not see the same benefits as MTB so I'm running tubes in 2 wheelsets on that bike. Different animal for MTB.
Same here. I find that latex tubes on the road bike give all the performance with none of the hassles.

PS: one more thing worth mentioning: this bike came with Reynolds AR carbon wheels, which are 8 years old and have a hook bead like a metal rim, so they can run tubed or tubeless. Apparently hook beads are a weak point on carbon rims, and the rear rim started to delaminate at that location. Reynolds replaced it under warranty, so the rear rim is a Blacklabel 287, which is tubeless only, no hook bead. And it's the rear that leaks under low pressures.
 
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