I have to do a $700 or $800 "tune up" every 15,000 miles to keep the warranty on my Subaru. Before you laugh, I've had to use the warranty when something went wrong, and it's covered some of the costs of other maintenance I've had to do, so I'm not keen on blowing it. Anyway, it's been 2.5 years since the last of these "tune ups," and I've got about 4,000 miles until the next one.

The average American drives 12,000 miles per year, so bike commuting is saving me around $500 per year this way. If I biked every day, instead of most, it would be even more.