I have a Firestone tyre, looks almost new, very little wear at all. Inflates fine and holds its pressure. However, every now and then for no apparent reason, at speed or when ambling, it deflates all of a sudden. I've changed the rim, I've changed the valve. There's no sign of a hole, and definitely no hissing sound when it's inflated. WTF? Anyone else experienced this?

Have you tried massively over-inflating it and submerging it in water?

TBH, if it's been deflated "at speed" - especially a couple of times - I'd regard it as very suspect, regardless of whether you know what's causing it to go down or not. The internal structures of a tyre can get quite badly damaged in short order.

Is it a recent Firestone or an older one?

I've had a Firestone come off the rim on the MOT brake rollers, but it was underinflated.

Are you sure you're running an appropriate tyre pressure? Might be worth double checking the gauge you're using. I knew mine was low, I'd checked it and then forgotten to pump it up. Visually it looked OK though.

Snowy
have you had a good close look at the sidewalls?

As Adrian says, just one incident of running flat, even for a short distance, is usually enough to cause damage which renders a tyre unsafe for further use...

ken

I wonder if this could be caused by rust on the inside edge of the wheel rim where it seals against the tyre beading? Possibly when the wheel happens to be sitting in the 'right' (wrong) position, the flexing of the wall is enough to break the air-seal, whereas otherwise you have been 'getting away with it'...?

But, it needs investigating - very scary. I'd have thought the 2CV tyre would be an easy DIY removal job with a couple of levers (or screwdrivers...!)

I wouldn't bother with firestones, every time I've had them on my car they just fall off the rims when cornering. pretty dangerous imo.

"Oh Gawd. If it isn't one thing, it's another!" as my Grandma said right before she croaked (quite cool dying words, eh?)

The rims are looking bit black and matt, since I had to drive 200m or so after the deflation to get off the busy dual carriageway, so I reckon the effing Firestone is bound for the landfill.

Now then, what to buy? I'm on a budget. Toyos?

BTW: thanks for your advice, chaps.

Toyos are my next tyres, since im also on a budget and they seem to have good reviews. i also got told nankangs are fairly good too. and cheap!