I’m certain that I can only raise more doubts than I can answer this question. And I do have a small rear view mirror on my touring bicycle. So if you are thinking of getting a mirror, think again and read this.
First let me establish my experience. I have a Zefal Spy bicycle mirror: a tiny little mirror that unnoticeably hangs of the left end of my handlebars. I have it for one year, and I took it on about 8000 km of bicycle touring roads. I’ve expressed my opinion on this little device, and I find it useful.
But there is a general problem with having a rear view mirror. Most mirrors are designed to fit on the end of the handle bars. So if I want to have a peak at the state of traffic behind me, I have to move my head and my view quite to the side. The side is mostly to the left, since I live in a right side driving environment. This process is quite a distraction from the road I’m taking. So for each of my mirror looks I have to check first the road in front if it is clear enough for me to have a moment of distraction. Now, with the mirror I have, being a very tiny one, this process takes longer, since I need some split of a second longer to see what and who is behind me. With a bigger mirror, this would be easier, since the objects would be bigger and clearer. But still, even with a bigger mirror one must plan that moment of distraction. So the issue is whether I want to keep my eyes on the road in front or keep looking back to a car that would in any case have to overtake me somehow. And my knowledge of the existence of that particular car would not really change much.
I would also say that looking into a mirror is far les time consuming than looking back with your head. The later is also far more dangerous because sometimes this movement of the head to the back may cause disturbance to the balance, leaning the bicycle and leading to a movement to the side of the road that may cause an accident. While when looking into a mirror this deviation is not present.
I think that having a good set of ears may be much better than a rear view mirror. Due to the nature of the required time and concentration to look behind, mirrors are not that suitable for sudden movement. In the case for a sudden movement it is the ears that I use. I hear if a car is approaching and I know if I can go to the middle or the edge of the road. The sound of the engine will tell me if it is a car, a truck or something else. The vehicle does not need even to make any sound signalization, since I will recognize it from the engine noise only. This way I keep my eyes on the road ahead and I’m on the lookout for any sudden movements. And sudden movements are normal in the Balkans.
I am also inclined to describe the contrasting situation to my attitude on sound versus sight. It is the new technologies that create quieter vehicles. Vehicles that sometimes is difficult to hear, like the case of electric cars. In this case, good set of ears may not be sufficient. This situation is present more in regions with high level of economic development, like Western Europe or Northern America. In southern and especially eastern parts of Europe vehicles are much noisier and a good set of ears will do well.
For the purpose of this article I took off my handlebar mounted bicycle mirror so I could notice the difference. I did miss it. I kept looking to the side of my handlebar every time I would hear a vehicle approaching. But in an overall sense, I did not feel handicapped without the mirror. I realised that it is truly convenient to be able to look behind easily without having have to move my whole body to turn my head. And it does give an added planning advantage when riding along a road. In short – a mirror is practical.
Knowing all of this, I still would not put a mirror on my city bicycle. It would only be an item on my bicycle that could be stolen. I consider that city bicycles should be only the bare necessity and easily left at any corner on any street without a worry that it will be damaged. Mirrors do not have a place in this context. But you may have a different perspective.
Finally, if I do decide to get a new mirror, I think I would look at those big mirrors, with very big handles. The handles are so big that the mirror is raised at the eyesight level, so one does not need to look far away from the road. A fast glance would give the information needed. But these mirrors can be a nuisance when storing or transporting the bicycle. Another solution may be the glasses mirrors or even the helmet mirrors - a small, very tiny mirror that is placed on the glasses or helmet. They offer a true spy peak view, but at least will not make me loose sight of the road ahead.