Originally Posted by
vic303
rydabent is right--as a recumbent rider, I have to rely on mirrors on my bars (I run two). It is not feasable to look over your shoulder on a bent. I have tried a helmet/glasses mounted mirror, but with the option of using my headrest, this type of mounting requires constant adjustment as the positioning of it changes when using the headrest or not.
Also remember the body's natural tendency to steer in the direction you are looking--so as you turn around on a DF to check over your shoulder, your bike will subtly track toward the side you looked over...same thing in cars.
While you can train yourself to not do this sideways tracking... (I actually used to look behind me by looking upside down from a tuck position) the other disadvantage of looking over your shoulder is the time it takes... not a big thing in slower traffic, but in higher speed traffic, that time disadvantage can be exactly when someone from behind comes right up on you.