The recommendation to put the best tire on the front is for 2 reasons - 1, you steer with the front tire so traction is the most important there, and 2 if you completely lose traction on your front tire (whether it's a tire blowup, not enough tread, not enough grip in the wet, etc) you're nearly certain to go down immediately. It's happened to me (wet road) - there's not time to react. But if you completely lose traction on your rear tire you (so I've been told) your bike doesn't just fall over, you have a couple of seconds to react which is usually enough to put your foot down or something.

The far greater risk of a serious injury if your front tire completely fails is why it's recommended to put the best, longest life tire on the front.


That being said, most people simply replace whatever tire wears out and don't bother switching tires. Rotating bike tires is something people just don't do.