Tyres constantly losing pressure

Three out of the four wheels on my wife's 05 Zetec 1.6 Focus are consistently losing pressure by 5-8 PSI per week.

The tyres have been replaced and so have the valves. They are alloy wheels and look in good condition. Do alloy wheels deteriorate and lose air seal?

Asked on 31 October 2011 by theanalyst

Answered by Honest John
Yes, they become porous.
Similar questions
My 06 Ford Focus Ghia has 16" alloy wheels with some unsightly corrosion. Can I simply replace them with steel wheels using the same tyres, or does this effect performance? And where might I get such...
I have recently purchased a BMW 118d cabriolet on sensible 16-inch wheels with 205 55 16 tyres. These are not run flats but I do not trust the tyre repair and inflation kit to work and know that you have...
Can you tell me what the speed ratings mean on a set of tyres?
Related models
Superb blend of keen handling and ride comfort. Seats five in comfort. five-star Euro NCAP crash test rating.