Car back!
 

Do you typically know what is behind you as you ride?
Do you just look when you need to?
How do you know what's there, mirror, turn around, listen? Something else? All three?

Listen - constantly
Look in the mirror - about once every 10 seconds
Turn around - when I need to make a lane change

In city traffic its safe to assume there's always a car behind me. I look when I turn change lanes etc. I rode with a mirror once and I found it took my attention away from what was in front of me. Out on the open roads, I can hear them coming. But truth is I try to ignore the sound, no point in tensing up every time a vehicle passes. I found all a mirror did for me, was tell me what size of vehicle is coming and at 100 km/hr it doesn't matter if its a ford excursion or a smart car, it'll still kill me if it hits me.

Whether driving my car or riding my bike, in traffic I glance back every few seconds in my rear view mirror.

I dont have a mirror. But I do listen to the environment around me and take my cues from it. I really only look over my shoulder if I need to change lanes or take the lane.

I have a side mirror by Blackburn on my left handle bar end and I listen! I look to my mirror about every 15-20 seconds and glance over my shoulder from time to time. I have a rear taillight and a front LED for better visibility to vehicles.......overkill, maybe, but if it keeps me from being pavement, I will be the bike geek you talk about at the coffee shops......LOL! :D

No mirror, just good ears. Mirrors became too much distraction getting the adjustment right.

ears ears ears - -plus, if you're a commuter riding the same route daily you know when to expect a group of cars based on lights you go through, (or don't go through), and various intersections.

when i'm passed by a group of cars after red light i know about how many go through before it's quiet again for a bit.

Mirror. I look often on my two recumbents. Rarely on my upright. I'm not sure why the difference, but maybe because the mirrors are placed better on the recumbents.

Helmet mounted mirror. Most of my road riding is on busy suburban and urban arterials, or high speed 2 lane road, so keeping track of what's going on all around is vital. With a mirror like that, you only have to shift your eyes slightly to keep track of traffic coming up from behind. I like to "read" the drivers back there to get an idea how much attention they're paying to the job of safely passing me, and your ears won't give you a clue about that until they're very close. Granted I've never been hit from behind, but I've benefitted from knowing in advance a few times when I was about to be "buzzed". Also good to know how much room I'm going to get from a semi passing at high speed so I can prepare for the air blast.
I'll leave the mirror off for trail riding, but am never without it on the road.

Knowing what's behind you at all times is important for safety -- your mirrors can indicate a clueless or hostile person before your ears though hearing is also important. You can also anticipate problems and opportunities long before they reach you.

I have used helmet and glasses mounted mirrors over the years. I think they are superior to anything mounted on the bike because you can turn your head to see anywhere behind you (i.e. no blind spots) without taking your eyes from the road, there's less shake, and you can see everything without distance or size distortion.

I tried a mirror once, but I don't bother with one anymore. I look back if I'm planning to move laterally on the roadway or if I'm curious, but otherwise not very often. If the lane is wide and I'm between intersections then I am usually riding in a lane-sharing position; if the lane is narrow then I'm farther left. The only times I find myself self-consciously looking backward to see if a car is coming are when I'm riding two-abreast in a location where riding single file would help people pass safely.

If traffic approaches me from behind, I keep a straight line, unless it's a wide vehicle or an emergency vehicle. If it's a wide vehicle some distance back in a so-so width lane I merge toward the center of the lane to make it clear they have to change lanes to pass. If it's an emergency vehicle then I pull off the road.

I can hear if a car is following me at my speed, and so if it doesn't clear soon I may look back to see if there are other cars backed up behind it. If it's a two lane road and many cars are backed up, I'll pull over, but I don't ride enough busy two-lane roads to experience this often. Most of my routes are busy 4-lane or low-traffic two-lane.

A mirror makes finding a gap in busy traffic for a left merge more convenient, since one can postpone turning one's head until nothing appears in the mirror, but my usual routes are such that I don't need to do this very often.

-Steve Goodridge

I thought mirrors were superfluous, until I installed one on my bike. I like it for lane changes, etc. It's also informative on the bicycle paths to know when a cyclist is going to pass you real fast!

It doesn't weigh much and I just feel a lot more on top of traffic.

Count me as a mirror advocate too. I think it's helpful to know when a knot of traffic is coming up behind me, and is invaluable for scanning for gaps in traffic behind me when I'm preparing to change lanes. Less movement and takes less time than turning my head, although I still do that too just before changing, as a last check and to cue in the motorists.