Several owners have told me their SA advised them on the newer cars if your valve stems are black you can use the metal valve stem caps, yet if they are grey then you have to use plastic caps. The reason being they have changed the tire pressure monitoring on cars with grey valve stems and the metal caps would cause faulty readings. Something to do with the pressure readings reflecting back off the caps. However I checked my valve stems and they are grey and I have the metal Roundel caps on them... with no issues. Go figure. Anyone else heard of know of this isuue?