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OK, so been on road tubeless for about 10 years now and have a wheel that is losing air (down to "not much") over the course of a couple of hours. Not had this before; brand new tyre, no evidence of sealant anywhere on the rim/tyre interface, and can't hear any air escaping. I've re-taped it (two wraps) and cleaned the inside of the rim, so think the bead is fairly clean (they're a good few years old, can't remember when I built them) tightened the valve core, just at a loss. Any suggestions for what this is likely to be? I would have thought if it was losing air this quickly there should be sealant somewhere...
Get a spray bottle with some very dilute washing up liquid and wet the rim - inside at the spokes, at the valve, at the bead and along the tyre. Any bubbles will soon show you where the leak is. If it's the bead then adding a bit more sealant and doing the "Stans Shake" will likely seal it up.
Yeah I was giving consideration to dunking it in the bath and turning it round. I've already done the shake around many times, spun it like a good un, so I'm pretty sure if it were a small gap the sealant should have sealed it. I may just strip it down again, and clean it to "like new" if it goes down again 🙁
Have you tried changing the valve?
Had one doing this not so long back, no evidence of leaking even in water...switched valve and hey presto.
Might at least rule out the existing.
I was just about to re-post and say that it's not lost much air overnight and this was after me pumping back up yesterday and nipping up the valve core afterwards. It was obviously a little loose. It's an old valve but think the core is a replacement. CBA changing the valve now but I think that's sorted it in the short term. Everything pointing to the valve then!
Have you tried changing the valve?
Having had a similar issue with my new gravel rims and tyres, and after help on here, I added sealant, changed the valve cores and also got a hey presto moment.
Hey presta surely
Chapeau sir!! 😂
Was going to say a ride can help sometimes just to iron out a tiny leak, get everything settled - nearly flat after a couple of hours is too much air loss for this but if it's held reasonable overnight I'd go for an easy spin on it.
I had similar recently with a new tyre/reliable wheel set up. It would lose 40psi overnight. I ended up dunking it and found loads of seepage round the rim 'seal' (non seal). I just added more sealant and more shoogling until it stopped. I went through the new tape/new valve process as well obv before dunking cos you would wouldn't you...?
I've had problems with snake bite style punctures and Pirelli P Zero tubless tyres on Zipp 404 rims. They've twice almost snake bited which created a thin patch through which air could leak, but not sealant - which meant it never sealed and just went flat. The patches were right at the bottom of the sidewall where it touches the rim.
Total PITA, the only solution was to remove the tyre, and patch on the inside. Happened twice to the same tyre, hitting potholes.