What You Need to Know About Car Alignment

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Car Alignment 101

This is a mini series about car alignment and what you need to know and do prior you bring your car to a mechanic. Your knowledge can save you some money in the end if you know what you are talking about when you communicate to a mechanic.  Wheel alignment is an important factor in maintaining your car balance and ride quality.  It is really frustrating and annoying when your car doesn’t go straight or making a humming sound at high speeds.  Every time you run over a big pothole that you can’t avoid, there is a chance that the alignment on your car might be dislocated.

Wheel alignment is no rocket science.  The basic elements of alignment are really simple.  There are three basic elements to an alignment, which one of them isn’t adjustable by a mechanic.  I will go into that later.  Well, the three basic elements of car alignment measurements are caster, camber, and toe.  When you take your car to a mechanic for an alignment, a mechanic will determine these three measurements are within published specifications for your car.  You can find these measurements for your published car guides or you can do a bit of search on the Internet.

wheel alignment

As I mentioned earlier, you only really need to know two basic elements of alignment out of the three.  Thanks to the invention of the ‘good old’ McPherson strut (found on most American-made cars), most modern cars today have only adjustments for toe.  The camber and caster adjustment went away with the McPherson strut setup.

macpherson strut

Caster

Caster is the angle to which the steering pivot axis is tilted forward or rearward from vertical, as viewed from the side. A backward tilt is positive and the forward tilt is negative, measuring in degrees according to the radius of the wheel when looking from the side.  Positive caster usually tends to straighten the wheel when the vehicle is traveling forward, which gives the car a straight line of stability.  Just like the two front wheels found on a shopping cart, it has positive caster so you can push it in straight line with little effort in trying to steer it in a straight line.  Most modern cars don’t have caster adjustment, so how do you fix it? In case of a bend, it could be caused by any of the assembly components such as a spring column, ball joint, inner bearing, uneven worn tire, or lower control arm. A good diagnosis is required to determine which of these components are the cause to reduce the replacing cost. Caster has many factors that can cause it to misaligned.  I will cover this topic in the “Car Alignment Diagnose” series.

caster car alignment

Luckily, most cars are not really sensitive to caster settings, but it is important that the caster measurements are same on both sides of the car to avoid any tendency to pull one side.  In a simple meaning, caster controls the center of your car.  So if your car is pulling to the right or left on its own, sometimes you may just have uneven worn tires.

Toe In or Toe Out

Toe is the most important wheel alignment angle because it has the greatest effect on tire wear.  The purpose of toe is to make sure that the wheels are parallel to each other.  If both the wheels are not parallel when moving, you can imagine like your left foot wants to go left and right foot wants to go right.  When you are looking straight down on your car (bird’s eye view) and you see the wheels of your car are facing inward, toe is positive.  When the wheels are turned out, it is negative.  The toe-in and toe-out are very sensitive, only a fraction of an inch can cause the wear and tear of your tires.  Toe can be easily corrected with a couple of turns in or out of a nut to extend or contract the toe rod.  When the wheels have “zero toe”, they are theoretically aligned.

Toe car alignment

Camber

Camber is the angle of the wheel relative to vertical, as viewed from the front or the rear of the car.  When the wheel tilts outward at the top, the camber is positive. When the wheel tilts inward at the top, the camber is negative. The amount of tilt of a car wheel is measured in degrees from the vertical when looking directly to the wheel from the front or rear of the car.  Camber helps the car sticks to the road when the car turns a corner or going down/up on a curve ramp.  How much camber you need to tilt in or out is depended on how much load you normally carry.  Most commercial trucks have positive camber because they carry a heavy load, which makes the wheels to tilt inward.

camber car alilgnment

Sticking to the road is good because you don’t want your car to sway off to the side of the street or ramp.  But when you have too much negative or positive camber, your tires will not wear properly. Too much positive camber will cause premature of the wear on the outside of the tire and excessive wear on the bushings of your suspension joints.  Vice-versa, if too much negative camber will cause premature on the inside of the tire and excess wear of the suspension.

Camber also plays a role in the straight-line of your car.  If unequal side to side camber is off by one degree or more, it will cause the car to pull to the side with the most positive camber.

This is all you really need to know about the basic elements of car alignment.  Next series, I will go into a few simple steps that you can do at home in how to diagnose and pin point an alignment problem.

  • Boback

    thanks alot. text was very usefull.
    Boback – Persia – Mechanical Engineer
    bm_2712@yahoo.co

    • Vincent_Van

      The website had a design change a few days ago, so some of the pictures in this post were unlinked. They are up now.