My wife's Fiesta has three porous alloy wheels, the fourth is ok. On one rear wheel, over two weeks, the pressure drops from 26psi to around 16. The two fronts tend to go from 31 to 25 in the same period. Now I have never taken a wheel off and immersed it and this is just an assumption. However, to have three leaking tyres is unlikely and they are not that new but good tread. Does any one have a solution. All rims have the remote air pressure monitors, so the alarm always come up before driving. Piers