I use both a helmet and a bar mirror. The helmet mirror for when I’m on the hoods. I can see anywhere behind me by aiming the mirror with head position. The bar mirror is for when I’m in the drops that way I do not have to lift my head up to align the helmet mirror.
I figure that the more ways I can keep track of my surroundings the better.
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It's better to cycle through life than to drive by it.