Over the last few months, I have been topping up the pressure on one of the tyres but only every 3 or 4 weeks. The others have kept their pressure.
Yesterday it suddenly lost all pressure whilst driving (not too far from home).
The guys at the tyre centre (a well trusted independent firm) said the rim was corroded and that was causing a gradual leak. They tried their best to get rid of the corrosion but it has lost pressure again really quickly.
Will I need a new wheel?
I had had this problem with older alloys before. When new they will have something like a clear coat paint finish which protects against atmospheric corrosion. This has now gone and tyre fitters will brush goop on the inside rim before fitting a new tyre to compensate but a full wheel refurb might be a better bet - always assuming you don't have a faulty valve or cracked wheel.
Follow up... It went down again flat overnight. So I pumped it up again , right up to 41 this time. It hasn't gone down in over a week now including a 400 mile round trip on motorways.
I have no idea what solved it and when the problem will come back.
The rim would have to be extremely corroded for the tyre to lose ALL pressure suddently. I would get them to try cleaning it again and have the valve replaced at the same time. I would then have them take the trye up to the absolute maximum pressure it can hold and then take it slowly down to the correct pressure. I would then have them put it in a water tank and check for leaks. Due to the weight of EVs, I also run my tyres slightly above the recommended pressures.
I don't think you should have to get a new wheel, it unusual for leakage in the rim to go down that quickly, if you blow the tyre up then get a squeezy bottle full of water with a little washing up liquid, spray that on the tyre to see where it is leaking from, if it is the rim then you could try the tyre refurbishers, they may be able to repair it. Richy