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Alignment Basics

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On: Mon, Aug 29, 2011 at 10:51AM | By: Peter C Sessler


Alignment Basics

With most car owners, a wheel alignment is something they get around to—eventually. Typically, that will be when they finally get around to replacing the tires or when the steering starts acting up to the point where it can no longer be avoided. The problem with wheels going out of alignment is that it is a gradual process. You might notice that your car will pull to one side or another on a smooth, flat highway or it might vibrate abnormally. Sometimes, though, if you hit a humongous pothole, you’ll feel the difference immediately.

As usual, it’s best to eliminate the obvious before taking your car in for an alignment. You’ll find that uneven or low tire pressure will often have the same symptoms as wheels being out of line—especially with front-wheel drive cars. Low tire pressure in one of the rear tires will cause that tire to drag in relation to the other tires, thereby making the car pull to one side. So, the first thing to do is to make sure all the tires have the same amount of air, then go out on the highway to see if it pulls to one side or the other. If, on the other hand, you notice that your front tires are wearing unevenly, especially on the inner or outer edges, then just go ahead and make the appointment. The only problem I have with alignments is that a few minutes after they take the car and put in on the rack, the mechanic comes out to tell me that I also need hundreds of dollars of front end work as well or “the alignment just won’t hold!”

There are three areas where adjustments are made during a wheel alignment. The first is Caster.

CASTER

Caster refers to the angle made when the wheel is tilted forward or backward in relation to an imaginary line drawn between the upper and lower ball-joints. Negative caster occurs when the front of the wheel is forward of that imaginary line and it is positive when it is behind it. Caster does not affect tire wear but it does make a big difference in how a car feels. Ever wonder why the wheels tend to return to straight after you go through a turn? It’s positive caster that does that. It gives the steering an on-center feel and makes the car stable at high speeds.

The drawback is that it makes the steering feel heavier at low speeds. The opposite holds for negative caster. It makes the steering feel easy at low speeds but it makes the car feel unstable at high speeds. Grocery cart front wheels follow the same principle. The front wheels have lots of built-in positive caster so the cart steers straight down the aisles.

CAMBER

Camber has a major effect on tire wear and directional stability. To get an idea of what camber is, all you have to do is to look at your car’s front tires from the front of the car. Negative camber refers to the angle made when the top of the tire leans toward the body of the car. Positive camber occurs when top of the tire leans outward. Generally speaking, most cars have 0 to 1 degree negative camber because that helps handling. As a car turns, camber changes, and a little negative camber when going straight turns into 0 camber during a turn thereby maximizing the amount of tread that’s on the road—and that helps handling.

TOE

Toe is the last adjustment in a wheel alignment. This time, visualize looking at the front tires from above the car, as though you’re looking straight down on them. If the front of the tires point inward in relation to the rear, the toe is said to be “in”. If the fronts of the tires point outward, the toe is “out”.

For rear wheel drive cars, generally, you’ll find that the toe is set in. As the car moves forward from rest, there is a tendency for the front wheels to move slightly rearward in relation to the car’s body. By setting the toe slightly in, when the car does finally get moving, the toe will be closer to zero—in other words, the toe compensates for the built-in slack in the front suspension. The opposite is generally true with front-wheel drive.

Most experts agree that toe is the most important setting when it comes to handling. Toe has a direct bearing on whether a car oversteers or understeers. However, for a proper alignment, all three have to be set to factory specifications and once again, your car will steer straight and true.

There’s not much you can do in terms of a “high-performance” alignment. I usually tell the mechanic to put in as much positive caster as possible as it tends to improve on-center feel and steering wheel return. Dialing extra negative camber will hasten tire wear and so it isn’t recommended unless you do a lot of slalom racing.




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