Originally Posted by mcours2006

I love my helmet mounted mirror. I couldn't ride without it. If you do a lot of riding in traffic it's indispensable. I have more confidence to ride out further from the curb as I can see what's behind me. Consequently I get a lot fewer close passes. I can get into a left turn lane more easily as I scan the traffic from behind.

If you're riding on trails all the time you probably don't need a mirror.