I used bar and/or helmet mirrors for a long time. The helmet mounted and glasses mounted mirrors made a huge blind spot up and to the left, which can cause a problem in city traffic. I settled on a bar mounted mirror on my commuter and am now completely hooked on it. I have a road bike with no mirror and it drives me crazy not having it. But now the porblem is I was so fat I could not get down in my drops and ride comfortably, now I can but with the mirror I cant reach my brake. So I am again rethinking the mirror. I know I have to have one of some sort. It helps seeing traffic from further away than a glance over my shoulder, especially when it is dark.
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Good Night Chesty, Wherever You Are