I've been thru some problems with losing tire pressure and wanted to share so others can benefit from my experience.

I'm on my third set of tires: Pirelli runflats that came with the car (got 25K miles), Michelin Pilot Sport A/S3s (50K miles), and now Pirelli Stratas 30K miles and still going strong).

I've had problems with the tires losing pressure on both the Michelins and Stratas. I've recently been working with Discount Tire to figure out what is going on. We have figured it out. I hope.

Back in the Michelin days I replaced the valve covers with MINI Union Jack valve covers. On a trip to DT a couple of weeks ago they discovered A) a bad valve stem and replaced it, and B) on 2 of the tires the Union Jack cover, when tightened fully, was slightly touching the valve stem, causing the tires to VEERRYY slowly lose air. After this trip I left the valve covers off for testing.

Three tires are good. One tire still leaked, about 10 psi over 2 weeks. I went back today and DT found a nail in the tire which they repaired. I've left the valve covers off and will wait a few weeks and see how well the tire pressure maintains.

The too tight valve covers was a surprise. The other 2 problems were not a big surprise.

 

I've heard of quite a few problems caused by those aftermarket valve caps. I stick with the rubber/soft plastic ones myself.