I was working on my truck this morning and had a milk crate by the front wheel to stand on. I was just standing there talking on the phone when I saw a little wiff of smoke so I looked closer and the crate was melting. The sunlight was reflecting just right off of some place on the wheel to concentrate it and make a hot spot. Must have been acting like a parabolic mirror. This really surprised me. The wheels are '01 factory alloys.