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Loss of tyre pressure

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barry65

New member
One of the rear tyres on my 996 Turbo is consistently losing air, about 2 lbs a week. I can't find anything like a nail in the tyre surface.

I assume the valve is faulty. Is it possible to have the valve replaced to cure this ? Would it be best to take it to the Independent garage I bought the car from, rather than a fast fit tyre place ?
 

I have had a similar problem, it turned out to be air escaping through the ally, a good tyre many will be able to tell you. To check the valve you could (this bit is not tasteful) put some spit on your finger and once the valve cap is off put the spit on the top off the vale to see if it bubbles up.
 
Sometimes it can be as simple as having the tyre reseated...
I had a rear that was the same and the removal and refitting cured it.. why??? no idea, possibly dirt

garyw
 
I had a similar issue on a brand new tyre. I got the guys to remove tyre and they just cleaned inside the lip of alloy (sometimes paint or residual rubber from lip of old tyre) and used a bead seal product. No issue since.

Another thing to consider is how old is the tyre, sometimes with age tyres can start to leak small amounts of air through small virtually invisible nicks from pure use.
 
The oxygen molecules do leak through the rubber, my local tyre specialist recommends using Nitrogen, they charge about £2 per wheel and say that it can last for the life of the tyres, baring punctures.
 
I think you'll find the use of Nitrogen is due to less expansion when temperatures rise (hence more consistent tyre pressure, especially when used for competition), compared to a regular 'air' mixture.

Normal air in tyres is not pure Oxygen anyway - air contains approx 78% Nitrogen and 21% Oxygen.

And in any case Nitrogen has only 7 protons and 7 neutrons, rather than 8 of each with Oxygen, so N atoms are smaller than O ones.
 
I think you might find this interesting
http://www.tyresave.co.uk/nitrogen.html

All gases, as I recall from school chemistry lessons, change according to Boyle's Law and Charles Law. If you heat the gas and keep the volume pretty much constant (as inside the tyre) then the pressure will increase. As I understand it the problem with "ordinary" compressed air is the amount of water vapour present. The nitrogen used to inflate tyres (aircraft and cars) has a very low water content and the change in pressure due to heating is less as a result. It appears that "dry" air would have the same effect nitrogen in maintaining pressure. Put "water vapour tyre pressure" into Google - it will keep you amused for a bit!![;)]
 
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