Once slapdash people said “Set the toe and let ‘em go.” Maybe those same people have now changed their slogan, changed it to “Green means Go.” But they’re just as wrong as they were before.

Alignment machines often color-code the dis-play to indicate when adjustments fall into the specified tolerances, green usually meaning the parameter is now acceptable. This is not a mistake or a shortcut on the part of the alignment machine manufacturers: they have to calibrate their machines by the specifications given them by the carmakers. And those same carmakers are in the business of keeping their costs under control. To set a parameter within a thousandth of an inch costs a certain amount. To set it within a ten thousandth costs very much more, not just ten times as much. So most carmakers’ specifications have a certain tolerance, a range of adjustments anywhere within which the machine should function satisfactorily. They are betting, of course, that one tolerance will be in one direction and the next in the other. But if all the tolerances are in a given direction, we can have a machine that is, paradoxically, out of adjustment even though every-thing is within specifications! This is sometimes called tolerance stackup, and the only real preventive is probability — it’s just not that likely all the specifications will vary the same way very often.

But sometimes they do! And those times the motorist must depend not on the alignment machine’s ability to sort out the major suspension angles quickly and correctly. In those cases, only the skilled alignment mechanic, who knows what it means when the angles all tend in one direction, even if they remain within the permitted range.

Put to the Test

So let’s consider a case where a very good alignment machine, operated by a skilled person who knows exactly what he’s doing, gives us nothing but green display patterns. If everything’s in the green, are you done? Does that necessarily mean the alignment you’ve just finished is a good one, one that provides control and steering, tire life and braking as much as such adjustments can achieve?

The surprising answer is, no. The car can still be misaligned.

To test this, I schmoozled his 1999 Acura from Import Service’s publisher, Chris Ayers. It’s relative child’s play to put a technical hoax over on him, and he had no idea what I was up to. If I’m still technoscribbling here next month, that will show either that he’s a good sport or that he still hasn’t read this article.

I first took the car out for a road test to assess the steering and alignment qualities from the driver’s seat. This is no different from a test drive to confirm a customer’s reports of problems, except the customer here had no problems to complain of: We were going to create them. The car tracked perfectly at all speeds up to, perhaps even slightly beyond, the legal limits. Braking, either mild or hard, had no discernible effect on the steering feedback or direction, and the car behaved the same way in both directions.

Cautious Caster Capers

A driving test I like to use for caster involves finding an empty parking lot and turning the steering wheel all the way to full lock. Note: only professional mechanics should employ this test. The chance of vehicle damage or personal injury is too great for even a careful amateur to attempt. This is not something for do-it-yourselfers or hob-byists or car enthusiasts to try. Observing geometric phenomena while accelerating in tight circles (especially backwards) is not a natural driving skill, but a controlled experiment. If in addition something unexpected happens, you need a mechanic’s reactions, not just a driver’s, to cope with it.

For most cars (there are some exceptions), if you release the steering wheel and accelerate for-ward, the steering will wind itself to the center, straight-ahead position. It will do so, obviously, in the same manner with the steering turned left or right, and this Acura did just that. This is exactly what we expect.

Then I do the same test, but with the car in reverse. Since the geometric forces are exactly inverted on the front end, the steering should stay at the full lock — not jammed so hard against the lock as to make the PS belt squeal, of course, just enough to push it full left or right. Most cars will slacken the turn slightly as you ease off the throttle, as a rational person is apt to do backing up in a circle in a parking lot. The Acura behaved exactly as I expected again. Evidently, from the seat-of-the-pants tests, the alignment was correct.

The Edge of the Green

Then I took the car to Euro-Car in Norton, Ohio. Euro-Car is a three-generation shop doing work of a quality few new car dealerships can even aspire to match. The Demrovsky family, who own and work at Euro-Car, have been very generous with their time and their shop’s resources, not only for us at Import Service, but for you who read our magazine, too. Many photos you’ve seen in our pages have been shot at the Demrovsky’s shop, and many stories formulated or questions clarified there. If we credited them with every favor they’ve done us, you’d suspect the fix was in.

Besides their time on the job and generosity, as you can see from the photos, they also have the best equipment obtainable. Their equipment, not much to my surprise, confirmed that all the Acura’s alignment numbers fell into the green specification boxes. But I wanted to push the case, so Euro-Car’s Duane Hovey working with Brian Demrovsky, set each rear wheel to the maximum allowable left toe – toe-out on the left; toe-in on the right, but all within ‘green’ specs. Then they did just the opposite on the front wheels, setting maximum allow-able toe-in on the left and maximum toe-out on the right.

While there are aftermarket eccentric bushings you can use to change the Acura’s front and rear camber and the front caster, that seemed a bit much of a time-favor to ask.

Back on the road later and the next day, the results were subtle but undeniable. The caster tests were unchanged, but then, so was the caster. But you could no longer comfortably let go of the steering wheel at 70 mph. The car didn’t whip off the road like something horribly out of adjustment, but you didn’t care to release the wheel, either. Braking, of course, had no perceptible effect because we’d done nothing to the brakes.

Stack ‘Em Up, and Park the Car…

Now suppose we’d pushed all the specifications to their ‘green’ limits. Suppose we coupled the toe adjustments we made with as much left-pushing camber as we could dial into the rear end and as much right-pushing as we could into the front. Suppose we maximized caster on the right and minimized it on the left. Suppose our right tires had the minimum inflation pressure and the lefts had the maximum.

You get the picture. The car would gradually become almost undriveable even though all the alignment numbers stayed in the green. It is true that the chances of all the variables stacking up in just the right way to maximize pull are low, but it’s also true that there are about 200 million cars on the road, and some of them have exactly that kind of tolerance stackup. Many more have milder cases, such as this one we artificially induced in our publisher’s Acura.

The moral of the story? You not only need a good alignment machine to do a good alignment. You need a good alignment mechanic, one who understands the suspension and steering angles, one who understands what will happen if this or that angle approaches the limits. A shopowner who owns a fine alignment machine can be proud of his equipment. A shopowner who employs a fine alignment mechanic can boast even more: he can be proud of the work his shop puts out.

This article is a kind of thank-you note to Al Mytyk, who used to teach alignment and suspension at Federal Mogul’s Ann Arbor Michigan technical training center, which has been moved to St. Louis. The basic idea of this article was his; my own contributions are limited to words and photos — and any mistakes I’ve introduced! Thanks, Al, for all the things I learned from you!