Persistent flat - head scratching alert!

[Bass Culture]

I've only recently joined so be gentle with me, but I've run into a particularly bemusing issue with my Cotic Cascade gravel bike. I've had the bike a couple of years and have enjoyed taking it out on road and off road runs. I was originally supplied with a tubeless set up. Being a numpty (I'm 63, tubeless wasn't a thing in 'my day'!), I hadn't realised the sealant needed regular topping up, so no surprise when I got a puncture at the beginning of this year, it didn't seal. After trying to service the tyre by topping the sealant (Stan's) it still wasn't sealing - however, this is quite possibly because I was pumping it up, rotating the wheel to rest on the puncture, but leaving it overnight. Again, I'd not realised that it should be ridden straight away to help the sealant circulate around the tyre and do its job. So, based on the fact I'm a fairweather cyclist and tend not to ride too much over the winter, I decided tubes might be a better option for me and bought a couple of Aeron TPU tubes. This is where the fun starts! After installing the tube in the rear tyre, I left it and took it out for a ride a day or two later - about 16 miles or so along a local canal and cycle path, mostly tarmac with occasional branches etc. Put the bike away after my ride and when I returned to it the next morning, the rear tyre was completely flat. I obviously assumed I'd punctured again so removed the TPU inner tube. However, at £20+ each I was going to repair and reuse it for emergencies. When I took it out to locate the puncture though (pumped to about 5 psi and passed through a bucket of water) there was no air leaking at all! I presumed therefore that I must have knocked the valve or something (though there was air wasn't obviously escaping from that either) and reinstalled the same inner tube. When I pumped it up to full pressure (about 30psi) there was air started escaping through the original tyre puncture that I had at the beginning of the year! And sure enough, the tyre has deflated overnight, now I've come back to it this morning. Same again though - removed, tested in a bucket of water and no leaks apparent.

I'm scratching my head about this now and don't know whether revert to tubeless or persevere with tubes and buy a couple of butyl ones. Obviously, when there's a tube in, logic dicates the tube can be the only thing that the air is escaping from! However, there is no obvious leak but the tyre slight deflates overnight. Has anyone ever come across anything like this before?!

 

[N0bodyOfTheGoat]

I've yet to try anything but butyl and in more recent times latex tubes on my bikes, so I'm not writing from personal experience...

When you spotted the puncture on the tyre in tubeless mode, did you try filling the puncture with a tubeless worm or mushroom (I think on inside of puncture)?

Did you remove the old dried "sealant animals" and check for the offending object inside the tyre, before adding new sealant and later the TPU tube?

Some TPU tubes have removeable valve cores and can be injected with specific tubeless sealants, for example the Craft Cadence ones, who have a 4 for the price of 3 deal (~£54) which I'm thinking of trying with my gravel ebike.
https://craftcadence.com/products/superlight-tpu-inner-tubes-road-or-gravel?variant=55027073810812

 

[Webbo2]

A couple of things to note TPU tubes lose pressure quite quickly and you should never inflate one outside of the tyre as they deform and don’t go back to the original shape.
Did you check the inside of your tyre to find what caused to original puncture. Also 30 psi seems rather low even for a gravel tyre.

 

[midlandsgrimpeur]

It may well be punctured. I had TPU tubes that were punctured but showed no obvious signs, I could pump them up and initially no air seemed to escape and no bubbles in water. Left overnight and flat the next day. I can only assume the punctures holes were so tiny that there was nothing obvious to the naked eye or ear.

 

[Bass Culture]

Interesting, thanks all. Yes, I did plug the original tyre puncture and checked thoroughly the inside of the tyre for sharp objects or protrusions before fitting the inner tube. Anyway, I've contacted the supplier and today reverted to tubeless to see how I get on again with that. I used an old tube patch on the inside of the tyre to cover the original puncture from the inside. Thanks for your replies all, much appreciated.