| Ruth,i had a similar problem on a quattro ur a few years back,shortly after fitting new tyres- what i done was brush some diluted fairy liquid around the rims and valves when the tyres were warm(when the pressure had increased slightly) the very slow trail of bubbles revealed that it was in fact leaky rims- i took the car back to tyre shop and they removed tyres and brushed some sort of rubber paint on the inside if the rims just where the beads of the tyre sit and this cured the problem |