After you've spent a day washing and waxing your pride and joy, you look forward to giving it that final stroke: when you run your hand across the freshly waxed paint, just to feel how smooth it is.

There’s a lot of gross, nasty stuff on the road. We’re not just talking about poorly modified Jeeps and de-catted Mustangs here, either. The road is a dirty place, and that’s obviously why your car ...