Why does my rear tyre go down?

[mercfunder]

Just fitted 4 new tyres on OH's car, offside rear seems to lose about 4 psi over a couple of weeks whilst all the others are OK.
The alloys are all in need of a refurb, could it be that this one is losing pressure through the alloy?, rims don't appear to be damaged.

[Ricky_M]

Could be a dodgy tyre valve. Make a really weak mixture of fairy liquid and water and chuck it on the tyre valve, it should bubble up if air is escaping.

Have you checked the inner face of the rim for damage? You could just be unlucky and have a slow puncture.

[balls-out]

I used to get this on my wife's Citroen AX GT. A tubeless tyre needs to seal on the wheel. If the alloy is all furry it can't.
I took it back to the tyre fitter and he used some nasty looking black mastic onthe inside rim to make a good seal.

The alfetta GTV alfa was famous (OK not that famous, but known in Alfa circles) to suffer from 'porous' alloy wheels. The alloy itself actually would slowly let air out. All the tyres on my GTV6 required regular topping up.
Only Alfa could produce a wheel that didn't hold air...

Edited by balls-out on Tuesday 10th August 17:50

[flemke]

mercfunder said:

Just fitted 4 new tyres on OH's car, offside rear seems to lose about 4 psi over a couple of weeks whilst all the others are OK.
The alloys are all in need of a refurb, could it be that this one is losing pressure through the alloy?, rims don't appear to be damaged.

If I may rephrase the above post slightly:
The tyre bead has to seat well against the inside lip or flange of the rim. Sometimes corrosion will develop somewhere along that inside surface, the paint begins to bubble, which presses the hard rubber bead of the tyre slightly away from the inside lip or flange, and you lose the air-tight seal.

[davepoth]

Had this just yesterday, tyre had a small hole on the sidewall.

[007 VXR]

Ricky_M said:

Could be a dodgy tyre valve. Make a really weak mixture of fairy liquid and water and chuck it on the tyre valve, it should bubble up if air is escaping.

WHS ^^^

had this on mine

[WhoseGeneration]

balls-out said:

Only Alfa could produce a wheel that didn't hold air...

Edited by balls-out on Tuesday 10th August 17:50

Nope, Subaru did too.
Early days of UK Imprezas, cars on stands in Dealerships, whilst wheels were away for "sealing".
Quite why they were not just replaced with known quality wheels remains a mystery.