Slow puncture, garage couldn't find it

[essayer]

Anyone had this?
Slow puncture, took a few days to go flat, pumped it up again and another two days, flat.
Took it up to the tyre place today and they sprayed bubble-stuff all over it, absolutely nothing visible and nothing that could puncture it.

They thought that it might have been something in the bead which unseated itself once it went flat (!)

The tyres have been on for over 6 months and I'd be very surprised if it was someone playing silly buggers!

Just the garage being useless, or could it really have been something in the
bead?

[Rickyy]

Is the valve holding air?

[davepoth]

The garage have a bit of a point. Once the pressure gets too low the bead isn't effective any more, which makes the air leak out faster. Of course that means you have air loss from somewhere, probably a slightly leaky valve. Probably best to inflate it properly and watch it for a week or two.

[Stuartggray]

Best way to check this is to put a tube in the tyre. If you have low profile wide ones, probably not viable.

[crossy67]

davepoth said:

The garage have a bit of a point. Once the pressure gets too low the bead isn't effective any more,

But how does the pressure get low in the first place without a leak (puncture?)

You could have a cracked or porous wheel or leaky valve etc. You need to get the tyre and wheel dipped in a big bucket of water as a whole component. I have only ever seen it done this way in the past.

[Hasbeen]

I had one that would go flat a few times a year, that no one could find. It would be fine for months, then go flat.

The wheel had been curbed & had minor damage to the rim repaired, so it was totally invisible

We still aren't sure, but we took the wheel back to the alloy place. They could find no fault, but thought the leak may have been between the bead & the rim, & only occurred when the thing was parked with that spot down, distorting the tyre.

They ground the area out, & filled it with weld, then machined it fair, & it never leaked again. To complicate this, I fitted new front tyres at the same time. I was not too interested in finding the fault, just eliminating it.

[surveyor]

How old is the car? Alloy wheels do sometime become porous and need a refurb to persuade them to keep the air in.....

[Hasbeen]

The car is a TR8, so getting on a bit, but the wheels were only 3 years old, & from a top maker. It could have been the tyre bead was unsettled by the curbing, but no trouble since.

[saaby93]

Had both
Porous Alloys - painting the inside seemed to fix it
Porous sidewall after hitting a large pothole - it began to bulge a few months later