Picture this: you are cruising down the highway on a rainy afternoon, music playing on the radio. You flick your turn signal to merge left into the fast lane, glance quickly at your side mirror, and see an empty stretch of road behind you. You begin to glide across—only to be blasted by the terrifying sound of a truck horn right beside your door. Your heart jumps into your throat. You jerk the wheel back just in time.
What happened? You didn’t forget to look; your mirror simply failed to show you what was hiding right next to your rear bumper.
Every driver knows that adjusting side mirrors is the first thing you are supposed to do when getting behind the wheel. Yet, surveys by automobile associations across Europe and North America show that a startling number of experienced drivers still adjust them incorrectly every single day.
Take a close look at the image above: Which mirror is adjusted right—A, B, C, or D?
Breaking Down the Mistakes
To find the right answer, let’s see what goes wrong in the other three setups.
Mirror B: The “Selfie” Mirror
In Mirror B, nearly half of the glass is filled with the side of your own vehicle and your rear door handle. Many new drivers do this because seeing their own car feels comforting and familiar. However, your car isn’t going to hit itself! Wasting valuable mirror space looking at your own paintwork creates a dangerously massive blind spot where entire cars can vanish completely.
Mirror D: Lost in Space
At first glance, Mirror D looks fantastic—you see a minivan, a motorcycle, and a truck. There is plenty of traffic in view. But notice what is missing: there is zero reference to your own vehicle. Without seeing even a tiny edge of your car, your brain cannot accurately judge distances, angles, or depth. You cannot tell whether that motorcycle is directly alongside your rear quarter or three lanes away.
Mirror C: Too Much Comfort Zone
Mirror C is how driving schools taught people decades ago. You see a clear view of the road, but your vehicle’s flank still occupies around a quarter to a third of the frame. While better than B, it overlaps significantly with what your interior rear-view mirror already shows, leaving a notable blind spot right at your 4 o’clock and 8 o’clock angles.
The Winning Answer: Mirror A
The correct and safest adjustment is Mirror A.
In Mirror A, your own car takes up only a tiny sliver—no more than 5% to 10%—at the innermost edge of the glass, with the horizon resting roughly in the middle.
This tiny edge provides the exact spatial reference point your eyes need to calculate depth and orientation relative to your car. At the same time, the rest of the mirror is pushed outward to cover the adjacent lane, seamlessly catching vehicles the exact moment they leave your center rear-view mirror and before they enter your peripheral vision.
The Quick 10-Second Test
Next time you get into your car, try the standard SAE adjustment technique:
Lean your head slightly to the left until it almost touches the driver’s window. Adjust your left mirror until you can just barely see the edge of your car’s rear quarter.
Lean your head toward the center console and do the same for the right mirror.
Sit straight back in your normal driving posture.
When you sit normally, your own car should barely appear at the very inner border—just like Mirror A. It takes a few trips to get used to, but it effectively eliminates dangerous blind spots and keeps you, your family, and everyone sharing the road completely safe.
