Mirror images develop from time to time

By T Uncle

THERE'S more to automotive rear view mirrors than meets the eye.

Most drivers tend not to use them -- while those who do, rarely know how to adjust them properly.

A small lesson: Next time you're sitting in your car, waiting at the lights with a line of traffic either side of you, check both interior and exterior mirrors and determine whether or not you have left a blind spot in your rearview vision.

Most drivers do. They adjust the exterior rearview mirror so it looks along the side of the car and reflects the image of whatever is sitting right behind -- more or less replicating what is shown in the internal mirror.

The proper way to adjust an external mirror is to slightly angle it out from the car so it covers the "blind" spot that neither the inside mirror, the side mirror, nor the driver's peripheral vision is able to cover.

Stalking police cars once made a habit of taking up this position, just behind the car on the driver's side, synchronizing their speedometers before flashing the blue light and pulling the car over for speeding.

External rearview mirrors are absolutely essential for safe, responsible driving.

It's a surprise to learn that, in many countries, they have only been a legal requirement for a few years.

Today, they're fitted to all new cars and people are more concerned with how easily and conveniently they can be adjusted than anything else.

An internal lever that can allow the mirror to be set without putting a hand outside is the minimum requirement; electric adjustment is best, and is even better if it's part of an electronic "memory" system that looks after various in-car adjustments, including, for example, the driver's seat, and can be preset for individual drivers.

The function of an external rearview mirror is essentially a simple one, but the efforts made by car designers to maximize efficiency and ease of use seem almost out of context.

If an external rearview mirror emits as much as a small whistle when the car is cruising the freeway at 100km/h, passengers will be irritated.

If it doesn't cover a reasonable field of vision, the driver will be frustrated by it, and if the passenger-side mirror uses a convex reflector that overly distorts the view backwards, the driver will also be unsure exactly how far behind that fully laden dump truck actually is.

From the dental mirror-type to the modern, aerodynamic, flip- back design in use today, the science of automotive mirror design has come a long way.

The early, round mirrors common in the 1960s gave way to the wider-angled, squared-off designs that came into vogue in the 1970s.

These were, in turn, replaced by the molded plastic protrusions that worked fine except for one thing: A decent smack resulting from a slight misjudgment of distance would usually result in a shattered frame and a very expensive replacement bill.

Designers didn't take too long to come up with an ingenious solution -- the mirror, if struck, would simply fold back out of harm's way before snapping back into place without affecting the adjustment -- but owners of cars dating up to the late 1980s, with their rigid mirrors, find that is little consolation.

The challenge today is to find the correct aerodynamic shape.

Although car stylists are capable of exceptional feats when it comes to achieving low overall drag (Cd) figures, no one seems yet to have produced a mirror that does not create noise when the car is on the move, even with the windows wound up.

Designers use various tricks, such as designing the connecting arms to act as a sort of airfoil that minimizes turbulence and reduces noise or, in the case of BMW, adding small pimples that actually smooth the airflow in critical areas.

Holden's Vectra uses a styling trick that incorporates the side mirrors into the molding running around the base of the windscreen, but this probably has minimal effect on the aerodynamics.

Similarly, Saab's new 9-5 integrates the mirrors into the A- pillar where the extra-low "clamshell" bonnet shut line meets the leading edge of the front door.

Another feature of the Saab, also seen in various BMWs and Mercedes cars, is a special "tilt" operation that flicks the mirror down so the driver gets a view of the curb when reversing into a parking space.

When a forward gear is selected, the mirror automatically resumes its normal position.

Most European cars also incorporate heating elements in their side mirrors to provide a quick demisting effect on very cold mornings, but no one seems to have come up with a dimming switch, similar to that used on inside mirrors, that combats headlight glare from following traffic at night.

Maybe that will be the next step in the evolution of the external rearview mirror.