Originally Posted by
ks1g
A mirror (helmet or sunglass mounted) is excellent for easily checking what's overtaking you, especially when riding near fast-moving traffic.
I use a Look mirror attached to my glasses. I'd recommend getting used to a mirror... try not to let it distract you from what's in front. Remember to take a good forward look, before you go to the mirror and have it adjusted so that a quick glance gives you all the info you need. I use the first 30 feet of my commute to test brakes and check/adjust the mirror.