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Using a helmet-mounted rear-view mirror

2003, John S. Allen

Should a bicyclist use a rear-view mirror? That's a question without a single, simple answer. Mirrors raise important practical and legal issues.

Because bicyclists, unlike other vehicle operators (including even motorcyclists with their bulky helmets), do not have structures impeding their view to the rear, a mirror is not necessary for most bicyclists. Most get along well without a mirror. Some try a mirror but don't become comfortable with it. Every bicyclist should learn to scan to the rear without a mirror, and only then try a mirror.

And it is often enough misunderstood that it bears repeating: no driver has an obligation to look to the rear except when preparing a merge. For these reasons, a law mandating mirrors for bicyclists would do more harm than good, by creating grounds for a presumption of negligence on the part of bicyclists who do not use mirrors.

Am I contradicting myself when I say, then, that I have used a helmet-mounted mirror since 1976? Not really. There are many items of equipment that can be useful and beneficial, but don't deserve to be required by law.

For people who can learn to use a helmet-mounted mirror, I think that it is the best choice. It doesn't protrude past the end of the handlebar, it vibrates less than a mirror attached to the bicycle; and it is unobstructed by the rider's body.

An eyeglass-mounted mirror has  these same advantages -- and vibrates even less -- though it tends to pull the eyeglasses down and is easier to misplace than a mirror which is attached to the helmet.

Helmet- and eyeglass-mounted mirrors can look in different directions with a turn of the head. Sometimes when I am stopped, I will turn my head while looking in the mirror to check out the scenery, or people-watch. While riding, I turn my head slightly as I glance into the mirror to scan traffic directly behind myself.

But a helmet- or eyeglass-mounted mirror isn't for everyone. Like many bicycling techniques, mastering the use of such a mirror takes a bit of practice.

The instructions that follow are for positioning the mirror on the left side, as usual in a country where traffic keeps right.

As the mirror turns with the head, the angle of view changes. It is easier to figure out which way the mirror is looking if the left ear or helmet strap is just visible at the right edge of the mirror. To look directly back, the mirror should be placed as far left in the field of view of the left eye as possible without creating a blind spot. That is, the area in the left eye's field of view that is covered by the mirror should still be within the field of view of the right eye. People with large hairdos don't do well with these mirrors!

In order to see clearly with the mirror, it is necessary to learn to shift attention to the eye that is looking into the mirror. For this reason, people who are strongly right-eye dominant do better to place the mirror on the right side, even in a country where traffic keeps right. Many mirrors are designed to be affixed to either side of the helmet.

Charles River Wheelmen member Jerry Campbell
is right-eye dominant and wears his helmet-mounted mirror
on the right side (1982 photo)

campbell.jpg (37851 bytes)

People who have vision in only one eye should only use a helmet-mounted mirror if it can be placed high enough not to interfere with the view of the road.

In a crash, a mirror might possibly injure an eye. This risk can be minimized if the mirror has a breakaway mounting and especially if the cyclist also wears goggles.

I use Third Eye mirrors which have plastic stalks that can break; I repair them by drilling a 1/16" hole in the mirror's universal joint ball, and threading in a length of a bicycle spoke which I bend to shape and use as a mirror stalk. The universal joints also loosen eventually: I retighten them with a coating of cyanoacrylate glue ("crazy glue").

I find a mirror useful to preview gaps in overtaking traffic. Then before merging, I check in the mirror again, but I always also turn my head and look to the side. Vehicles (and especially, silent bicycles) which are close behind me on the left may go unnoticed because they are in the mirror's blind spot. By turning my head, I get a much wider field of view, very quickly. Also, turning the head to the left signals the desire to merge left.

When people with rear-view mirrors are riding together, whoever is leading can signal the next turn by hand, and the one(s) following can acknowledge the signal by repeating it, to be viewed in the mirror. I find this technique especially helpful on rides that are not following a fixed route.

The mirror also is useful to time merges into a stream of traffic, allowing me to take opportunities I might otherwise pass up, and also allowing me to be more courteous when I can allow a vehicle to overtake before merging. But remember, the mirror alone, with its limited field of view, can not tell when it is safe or advisable to merge. The mirror can only tell when it is not.

On a supine recumbent, a helmet-mounted mirror (or a handlebar-mounted mirror on each side) is nonetheless an important accessory, because it is not easy to swivel the head far enough to look directly back in the recumbent riding position. People with limited neck flexibility may have the same problem on an upright bicycle.

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Contents 2003 John S. Allen

Last revised 10 October 2006