I have an on one chunky monkey on a mavic En521 rim. Goes up tubeless and seems sealed but loses air completely within 24 hours. When soft I can squeeze the sides and let air out at the rim. I assume this means it hasn’t seated properly?
Do all tyres ‘ptwoink’ when setting up tubeless? Do I just need to ride it a bit? Worried it will roll off and cause certain death on the first berm…..

Not always. How far up the pressure scale have you gone?
Sealant?

Can we all use “phtwoink” a bit please to get it in the OED..it will be ace for scrabble.. especially if you are playing non Cyclists

Gone up to 65 psi as max on side of tyre. Do I need to use more?

I’ve recently fitted 2 tyres, same make/model, onto the same make/model of rim. Same amount of sealant in each. One phtwoinked, the other didn’t. I’m not dead yet.

What rim? Had no problem with chunky monkeys on flows.

You don’t always get the phtwoink but it does sound like yours aren’t seating. Bit of fairy liquid around the bead helps

Some ptwoink, others don’t. A more reliable check that the bead has seated is to look at the ridge that all manufacturers put around the bead, there should be a nice even gap of a couple of mm between the ridge and rim. If the ridge dissappears under the rim then it isn’t seated properly. If you’ve got up to 65 psi and the tyre still isn’t seated, have you lubed the beads with a bit of soapy water to help them on their way?

The ridge is evenly above the rim, and the tyre seems seated as it was when it had an inner tube in it. Do some rims and tyres just not work together?

Did you do the Stan’s shake ?

Sealant?

65 is scary high. Should seat at 20 or so, and maybe leave at up to 40 overnight, then reduce to riding pressures.

As long as it’s a tubeless ready rim you should be fine.
Hold on, a EN521 isn’t ?

Although hopefully an en521 user will be along to say they are fine tubeless……, just might not have the same profile in the bead hook (or hookless for some rims) area.

Have only tubeless’d my 521s with a rim strip but they are fine. Think I tried once without and it didn’t hold.

I’ve got an EN521 (& a 321) running tubeless, with Gorilla tape, Stans sealant and Geax AKA TNT Tyres.

It holds air fine but i’m not sure if it ‘Phtwoinked’ or not!!

WTB Nano went up tubeless with no noise whatsoever, a little underwhelming to be honest. But they’ve held and stayed up great

Rear is a spesh purgatory on en521 and it’s holding up fine. Using gorilla tape method, as I have for a while without issue until now…

No, I wouldn’t.

TBH I wouldn’t go above 40. I had a NN TLR fail at 50 odd I think and it made a hell of a bang (- something I imagine like firing a shotgun at a metal staircase), and completely covered my bathroom in stans goop. Not entirely pleasant. Probably dangerous if somebody had been nearby as well as I think it ping ponged around the room, judging by the black marks on the walls/ceiling.

I was putting it so high for the same reason as you, it wouldn’t seat/seal reliably.

Better option is to go for a short ride on it at 30 PSI or so.

Also have you tried holding it in a bucket of water to see where the air is escaping? Could just be the valve or something.

no – it’s seating:

The ridge is evenly above the rim, and the tyre seems seated as it was when it had an inner tube in it

again.

Sealant?

They don’t all phtwoink some popding and some just go up without any onomatopoeia

Brand new tyre? Clean rim? sometimes a bit of dirt trapped between the rim and the tyre is enough to slowly leak air

But if its staying up for 24hrs then its probably beaded fine, just needs more sealant then the Stan’s Shake or a quick ride to distribute the sealant.

I’d try this before more elaborate cures.

Funny this should come up now as the new minion I’ve just put on the back of my full suss went on silently. In all the years since I changed to tubeless I’ve never had one that didn’t seat with a bang.

You can see it’s seated properly but I think the noise just gives you that extra bit of reassurance 😆

Guess it depends on the shape of the rim bed, mine are quite flat and hookless so there’s not drama when seating tyres, I get a ‘bing’ sometimes but other than getting the last bit of the bastard tyres on in the first place it’s generally uneventful lol!

I’ve always gone ghetto tubeless with my 521s and they’ve both been fine and gone ptwoink with Maxxis, Specialized and Scwalbe tyres. I usually pump them up until the head is seated all the way around usually between 40-60 psi

I find sometimes I need to pump up to 70psi to get the tyres to get the bead to seat properly so the tyre is not wonky, or deflate and reinflate a few times. Dampening the rim with water helps things to slide into place. I don’t use any sealant.

Had the first ‘ptwoink’ moment I can recall recently, inflating one of my 35c Randonneur Pros on to one of my new Reet’ard rimmed wheels, gave me quite a shock! Wasn’t running tubeless and thought I had missed a bit of tube escaping the tyre bead to explode as I inflated. 😆

Reading earlier in this thread about big bangs brought back a memory of mine from ~1999, when I still had my lovely green Principia RSL racer. I can’t remember the tyre width but probably 20-23c, the max pressure was 150PSI and I decided to see how they rode near the max. As the track pump neared ~140PSI, a bit of tube escaped and went to about the size of a tennis ball in a split second, before an almighty bang like a shotgun that left my ears ringing for minutes! 😆

I just wanted to say ‘ptwoink’.