OK that's it!
Freak these people that steal the valve caps must be hunt down and shot. I was washing my car today and when I got to the wheels I noticed that I was missing a valve cap. I thought I might have forgot to tighten it properly the last time I was filling up on air, but as I walk around I noticed that 3 of the wheels were missing the caps... arg. The valve stems are hidden behind the spokes on my wheels, when I first got them I took me a while just to find them. These guys are persistent bastards!!
