factoid:

The E39 M5 came with special short, stubby valve stems- where the stem is located on the wheel is such that at high speed, the centrifugal force would cause a longer stem to flex, ultimately leading the abrupt stem failure.

NOBODY uses the right ones (except me I guess) ...special ordered at my local dealer and had to work hard to convince the parts guy they were different. When they came in (ordered 12) he was "well I'll be..."

So anything that increases the mass on the end of the stem is a bad idea for ANY car.

These are the ones that came with my 212 19" stock sport wheels. And they're still the best option because right now I have the metal caps with the BMW roundel and the metal fused so tightly on all 4 wheels I had to use pliers... even when using protection so it's not "metal on metal" it still scratched it because it's not exactly a high-strength steel. Not worth the $18 for a set. SHould go back to the plastic ones...

Man, you're full of good info. Thanks again! Just ordered (5).

NP. you're welcome!

The set you gave me are still fine. I only use them in the summer months, though. So likely it is the road salt that is causing them to corrode and fuse to the valve stems.

I have used the metal ones for years on various models of BMW's 335, 545, several X5's with no problem whatsoever. Except that somone stole one once. I have a set with the Roundel on it and I have a set with the M on it for my M. Maybe the difference is they don't use too much salt up here in Washington and that I typically check my tire pressure once a month so I screw and unscrew them frequently.

It makes sense except I don't think Statdoc sees too much salt in his neck of the woods.

I just lost one of the "mushroom" covers and leave on a long driving trip on Sunday so are these still difficult to locate?

Denalio posted the link to purchase these in this thread...