Why won't my tubeless tyres stay up?

I recently decided to return to tubeless on my two bikes, both with proper tubeless rims . Both sets went on and up with no problem but one keeps going down overnight. It is a new Ground Control, has sealant , seems well seated . I have deflated, added sealant, bounced it around but it still goes down . Any suggestions?

ride it

You’re a bad person?

Yeah, get out and ride it.

Remove the valve and wrap ptfe tape around it , quite a common problem leaking valves

Ridden it and had to stop and pump tyres to get home

wot cheekyget says, then (dab of mastic for me)

what tape did you use ?
are you sure it’s properly stuck ?
(could pop a tube in overnight to press it down)

Check the valve is tightly attached, then ride it. Some tyres take an age to seal, especially if the sidewalls were porous to begin with, but I’ve never had a tyre not seal eventually.

Check the tape is ok?

No tape, it’s a fully tubeless rim- no spoke holes!

Inflate it, then put in bath to see where its leaking?

“must” be the valve seating then (or the valve itself)

time for a bath (unless you have a big sink), as BenP says ? Look for whether the air’s coming from around or through the valve – if not through the tyre somewhere

(did you use fairy liquid to seat the beads?)

Same issue here with some beavers on giant own wheels. Front up with a new here fine, rear in a used beaver goes from 30 to 10psi overnight. Seeing as they are next weekends 24hr spares I’m this >< close to sticking a tube in.

…which inspired me to rip it off and start again. My yellow tape had lifted. Now cleaned, dry, re-applied and sitting with a tube in to push it down before going back tubeless his afternoon.

Can you figure out where the air is leaking from? Either porous sidewalls and you need more sealant & shaking or quite likely around the valve.

Assuming you have removeable valve cores, deflate the tyre, take the cores out and just give them a clean, pop them back in and nip em up tight, but not overly so. Tiny bit of dirt in one of mine may well have been an issue, but having done this, no more slow deflation.

I recently had a similar problem. As others have mentioned, check if the valve is seated properly in the rim channel. My rim channel was squarish and the valve was curved. I ended up having to tighten the valve lock ring with pliers. That jammed the valve into the rim channel and sealed the leak. Bought the proper valve a week later so I don’t need to have it done up so tight.