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Tyres losing air - Volvo 760 - Big Cat
One of our cars, an elderly Volvo 760, needs its front tyres pumped up every fortnight. Pressure drops from the set 28psi to around 15psi. Both tyres are quite new. I have had the valves replaced and this has not changed things. The car has alloy wheels - could these be causing the problem if they are corroding on the rim? The rear tyres which are the same age and make don\'t lose any air at all.
Tyres losing air - Volvo 760 - Dynamic Dave
The car has alloy wheels - could these be causing the
problem if they are corroding on the rim?


Yep, more than likely. Have you got clip on weights - the ones that are hammered onto the rims? These scrape off the paint and in turn eventually let the alloys corrode and the paint can become detached from the inner edge of the wheel. Tyre garage might be able to seal the tyres to the rims for you, but in the case of one of my previous cars, I ended up getting the tyres removed, sanded down the inner edge myself to remove all the flaking paintwork and then resprayed the inside of the wheels with Hammerrite silver spray paint. Never leaked after that.
Tyres losing air - Volvo 760 - Cliff Pope
Apart from corrosion of the rims causing imperfect seating, alloy becomes porous to air over time. You need to take the tyres off and paint the inside of the wheels - there may well be a special paint, but ordinary primer worked well for me.
It is standard practice I am told to fit tubes when replacing tyres on older alloys - the Michelins I just bought for my Volvo came with free tubes.
Tyres losing air - Volvo 760 - Andrew-T
Cliff - this suggestion has been made once or twice before on the forum. Is there any genuine evidence that alloy metal becomes porous after a few years? - sounds like a myth to me. Microcracking or what?
Tyres losing air - Volvo 760 - Cliff Pope
No evidence - its pure hearsay. But I was told it by an independent tyre retailer, I was given free tubes with my Michelins, and something, possibly the paint, did stop a leak in an alloy some years ago.
Tyres losing air - Volvo 760 - Dereksn51
And the other thing to remember is to get stick on weights when your wheels are next balanced.
Tyres losing air - Volvo 760 - Ivor E Tower
Cliff - not hearsay, it is true. My brother used to have a BMW 3-series with BMW alloys on it, and they also went porous because all 4 tyres would loose pressure regularly. Several tyre places told him about their porous nature and he had them taken off, refurbished and replaced on the car with the same tyres that had been losing pressure. No more problems after that.
Tyres losing air - Volvo 760 - DL
Refurbishing the wheels would include cleaning the bead mountings - the source of the air leak - not through porous metal.
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Tyres losing air - Volvo 760 - Cliff Pope
Refurbishing the wheels would include cleaning the bead mountings - the
source of the air leak - not through porous metal.
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Well, maybe. But all I did was slap on some Woolworths primer and then put the tyre back on again. hardly refurbishment.
Tyres losing air - Volvo 760 - Dizzy {P}
I think DL is right. A common cause of air leaks with alloy wheels is corrosion around the bead which lifts the tyre and allows air to seep by. Tyre depots overcome this by using a sealant, typically an orange paste, but I'm sure a coat of paint would also work, especially if the loose corrosion is removed first.

Aluminium can be prone to porosity during the casting process but I think it very unlikely to appear later if it wasn't obvious at the start.
Tyres losing air - Volvo 760 - Cliff Pope
Refurbishing the wheels would include cleaning the bead mountings - the
source of the air leak - not through porous metal.
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Well, may be. But all I did was slap on some Woolworths primer and put the tyre back on. Hardly refurbishment.
Tyres losing air - Volvo 760 - DL
Did you paint on the bead sealing surface of the wheel? If so, that is all it might take to restore the bead seal!
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Tyres losing air - Volvo 760 - Cliff Pope
Did you paint on the bead sealing surface of the wheel?
If so, that is all it might take to restore the
bead seal!
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Actually I think I deliberately avoided the bit in contact with the tyre!
You are probably right though, Dizzy et al, it was just the act of re-seating the tyre rather than any benefit from the paint.
It does seem a rather persistant bit of folklore though, and especially odd that Michelin of all people would have been offering free inner tubes to cure the "problem". (That may not have been a universal offer - just Cambrian Tyres in Aberystwyth)


BTW Dizzy - see my post on Triumph 2000s.
Tyres losing air - Volvo 760 - Dizzy {P}
Cliff,

I think the supply of inner tubes must have been the tyre fitters' idea. Michelin would never condone this because fitting inner tubes loses the 'slow deflation' benefit of tubeless tyres. When a tubed tyre gets a nail in it, it will normally lose its air very quickly and that can cause the vehicle to go out of control. It's a bad idea and the tyre fitters should have known better!

Yes, I've seen your Triumph post and given it a bit of a contentious reply, all in the interest of lively discussion!

Yours Triumphantly,

Dizzy.
 

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