Cycles of all sorts

The trivial sounding skill of looking back over one's shoulder is critical to vehicular cycling. It's not as easy to perform as it may sound because it requires traveling in a straight line while looking behind for up to a few seconds, and requires some practice to master. The natural tendency is to not continue in a straight line, but to swerve in the direction one is looking. Furthermore, it involves a momentary interruption in the process of monitoring the road surface and conditions ahead, which can be hazardous without appropriate preparation.

Looking back is essential whenever a cyclist needs to move laterally on the roadway or is crossing the potential path of other traffic for these reasons:

1. to make sure that they will not be moving into the path of someone else who may have the right-of-way, and
2. to communicate the cyclist's intention to traffic that needs to yield so that the cyclist can make the move, and
3. to make sure that someone is not about to violate their right-of-way. Many cyclists (even some with considerable experience) neglect looking back to check for traffic which may be about to overtake and then violate their right-of-way by turning into a junction where a nearside turn (a right turn in the U.S.) is authorized.

Looking back can not only suffice as a signal to overtaking traffic that a cyclist wishes to move laterally in the direction his head is turned, but has the advantage over hand signaling of not requiring removal of a hand from the handlebars (which could be hazardous in some situations). Some jurisdictions, however, mandate cyclists' use of hand signals to signal an intention to move laterally or turn.

Special mirrors are available for mounting on a cyclist's helmet, eyeglass, or handlebar. Such mirrors can be designed to reduce vibration, present an optimal field of view, or even (in the case of helmet or eyeglass mounts) to "break away" safely in the event of an impact.

A bicycling mirror enables the cyclist - with practice - to monitor overtaking traffic in less time than looking back takes. However, the effectiveness of mirrors is limited, particularly in urban situations and multi-lane traffic. Compared with motor vehicle rear vision mirrors, bicycle mirrors generally give a smaller field of view and are more affected by vibration. Looking back is important even if the cyclist is using a mirror.

Nevertheless, bicycling mirrors are useful for:

1. checking for presence of traffic to the rear that is nearby or overtaking before deciding to risk a look back that might (if not performed correctly) move the cyclist closer to those hazards, and
2. continuing to track other vehicles (particularly in open highway situations) that have already been observed by a look back.

Mirrors are sometimes the only reasonable option for monitoring overtaking traffic when attention on road and traffic conditions ahead must be maximized. However, a cyclist who relies just on mirrors to see if the way is clear of traffic not only runs the risk of missing details, but also misses the opportunity to use the look back to communicate intention to - or encourage attention or behaviour change from - drivers of other vehicles.

There are no legal jurisdictions or bicycle races in which mirrors are required (perhaps because of the impact on performance of the mirror's weight and wind drag in the latter case). However, a mirror is regarded by some cyclists as an important piece of safety equipment (especially for urban cycling and cycle touring) and by others as an effective way to reduce the stress of being surprised by passing traffic.