With a mirror (writes John. S of Louisiana), you know exactly what's happening behind in any situation. There's no guesswork. You can check for overtaking traffic before reaching for a bottle or pulling off the front of a paceline -- moves that could put you farther into the lane.

Gary G. of "far" northern California says he checks his mirror for cars behind whenever he sees one coming from the front. If it looks like two vehicles will meet where he is, he moves to the center of his lane and uses a rearward-facing palm to signal the driver behind to slow down. After the oncoming car passes, he moves over and waves the driver around.

"This has caused very few honks at me," Gary says. "In fact, it helps elderly drivers know what to do when otherwise they might not understand."

Like Gary, John and others who wrote, Ed uses a rearview mirror. It's stuck to the left side of his helmet. Other types mount to glasses (even inside the lens) or the handlebar.

Ed installed his mirror the day after he was grazed (intentionally) by some fun boy in a mufflerless yellow Mercury. That was 19 years ago.

Ed got over the mirror's dork factor pretty quickly and hasn't looked back since (pun intended). He figures: "It'd be dumb to drive a car without a rearview mirror, so why ride the same roads without one?"

It wasn't long before he realized the best reason of all for seeing behind.

A mirror tells you when no vehicle is coming. You can relax and take up more road. You can ride around potholes, cracks and patches instead of jolting over them, afraid that a car might be about to pass.

For mirror users, hindsight really is 20/20.