I had four tyres (Firestone CV3000) fitted to my van by ATS a few months ago. Its a big thing VW LT35 and on one tyre the valve is short and looks like a car valve to me. This tyre also went down from 60 to 50psi from July to Sept and I suspect the valve. My old tyres never lost pressure so fast. Even over a year sitting on drive unused they only lost about 5psi.
I should go back and get them to change the valve anyway as valve is too short to get access to when wheel trims fitted.
Any thoughts if the valve could cause this? The front tyres also lost a fair bit. 50 to 42psi over a few months. The other rear tyre has happily sat at the correct 60psi all this time.
Mark