There are a few offerings on the market now that allow you to check and adjust tracking at home, as long as you've got a flat level driveway (Gunson's Trakrite seems to be the most popular, but I'm sure I've seen others). If the things work as advertised, they should pay for themselves in 3 or 4 would-be trips to a garage or tyre-fitters, so has anyone used them, and what did you think?