Mirrors must be adjusted properly to get the best view of what’s behind you and beside you. Proper adjustment can help you back straighter and track your trailer wheels while turning. Let’s get started.

The first step is to drive straight ahead and stop with the tractor and trailer perfectly straight. Next, adjust the seat to the height and position behind the wheel you prefer. This will make a difference in how you see the image in the main mirror.

Using the mirror adjustment controls, or manually moving the glass if no electric controls are available, turn the glass so that you have a 90-10 field of view to the rear. You should be able see just a tiny strip of the trailer along the inner edge of the glass, about 10% — and the widest field of view possible, about 90%, beside the trailer.

Adjust the vertical field of view in the driver-side mirror so the back of trailer is about 1/4 to 1/3 of the way up from the bottom of the main mirror. This will provide a good view of the lane adjacent to the trailer as well as a good view of traffic approaching from behind.

For the passenger-side mirror, because you are further away from the mirror, the field of view will be narrower. In this case, it’s okay to keep the trailer as a mere sliver down the inside of the glass. That will give the widest view of the lane to the right of the trailer. Keep the rear of the trailer about 1/4 to 1/3 of the way up from the bottom of the main mirror.

When reversing, if you keep the same field of view in the mirrors as when you’re moving forward, you’ll know you are reversing straight.

Adjusting convex mirrors

The convex mirrors below the main mirrors provide a wider view of the area under and behind the mirrors. Because of the distorted view, convex mirrors aren’t very useful for determining how far an object is from the truck, but they are very good at revealing the presence of another vehicle or a pedestrian beside the truck.

When aiming convex mirrors, don’t bother duplicating what you can already see in the main mirror. Push the bottom of the convex mirror forward and the outside of the mirror outward. This provides the best field of view directly beside the tractor and far out to the right and left. That perspective is very useful while turning when the trailer wheels can no longer be seen in the main mirror.

If you have fender-mounted convex mirrors, position them to provide a view of the area between the front wheels and the doors. This is a critical blind spot on both sides of the truck. That blind spot is more pronounced on the passenger side. The worst blind spot on the driver’s side is directly behind the door, in the area between the door and the drive wheels.

The field of view

After adjusting the mirrors, pay extra attention to the view in the mirrors and observe traffic passing on the right and left. Notice where in the field of view a car disappears from view in the main mirror and appears in the convex mirror. Also observe when you are able to actually see the car. Learn these locations for future reference so that you’ll be able to instantly recognize what you see in the mirrors. You won’t always have time to try to discern what you see. It should become second nature.

Also, pay attention to the position of your trailer wheels when making a right-hand turn. Learn to recognize what an adequate distance from a curb looks like. That will help build confidence in your turning skills. And if you’re ever unsure if you are too close to something to proceed, either get out and look, or use the mirror adjustment controls to swing the mirror outward to get a clearer view.

Take the time to readjust the mirrors each time you drive a different truck. If you keep the field of view consistent, you won’t have to guess at what you see in the mirror.