Well with all of the lifting that goes on around here I figured it might help some of you to understand how an out of whack alignment will affect your vehicle and how to read those nice print outs they give you. I worked at a Sears Auto for 2 years in school and was taught alignments there and in school (mechanic). So I figured I would do a write up to help some people out because tires are spendy. Also I am not a teacher so if maybe find something confusing the way I explained it feel free to ask about it. I used degrees as measurements because that is what I worked with and what I was taught with. Some shops will use inches but usually you can get them to change the settings real quick in their computer to degrees and get you a print out with that.
First things first.
Not all alignment shops are created equal!Those nice little prints outs they give you with the red, black and green ink. Well they can be changed through the computer program to read in spec. If an adjustment is on the edge of spec, for example camber is supposed to be 0 degress to -.5 degrees if your actual camber is -.5 degrees it will highlight red. Now someone can go in to the computer and change that number so it comes out green. Catch me? Luckily where I worked no one pulled stuff like that but I have heard of it from other places. Take it to somewhere reputable and remember you get what you pay for! Some guys look at the computer screen and when it turns green its good. If you look at most specs there is enough room in there that when both wheels are on the opposite end of spec they will then cause a pull or tire wear. If there is .2 degrees or more difference between sides on Camber or Caster that will cause a pull. Just cause its in green writing does not mean its right.
Definitions of Camber, Caster and Toe. The big three.
Camber
Camber is the angle made by the wheels of a vehicle; specifically, it is the angle between the vertical axis of the wheels used for steering and the vertical axis of the vehicle when viewed from the front or rear.
Camber will pull to the most positive side. So if your Driver side has -.8 degrees camber and your pass side is .2 degrees camber your vehicle will pull to the pass side. Camber is not always adjustable on vehicles and may require shims on some. Also if you have seen these idiots that cut springs or heat them to lower their vehicle they get a lot of negative camber and end up wearing the insides of their tires out. People will set camber up a lot of different ways for racing. For our uses best to keep it right around zero. Or mfr spec.
Caster
Caster is probably a little more difficult for people to understand because you really cannot see it. It is a nice imaginary line that get some people confused.
Positive caster makes a vehicle more stable and helps pull the steering wheel back to center after making a turn. It will also cause heavier steering but with power steering and lighter vehicles it is not so much of a problem.
Negative caster will cause wandering and less stability. I have not seen any cars that have a spec for negative caster. Caster will pull to the most negative side. So if your driver side has 2.3 degrees caster and your pass side is at 2.8 degrees you will pull to your driver side. Caster does not have a lot of affect on tire wear unless you are correcting a pulling vehicle due to caster.
Toe
Probably the easiest and most misunderstood. Most people would assume that toe was the problem they had with a pulling vehicle. While an improper toe setting can cause some pulling it will wear the tires out faster then you know it. Toe mainly affects tire wear and steering wheel alignment. Toe measurement is the difference between the distance the front of your tires are apart as to the distance the rear of your tires are apart. Like in this diagram.
Thrust angle is the angle of the rear axle as compared to the front axle if viewing the vehicle from above. Can cause 'dog tracking' if bad enough. I am sure we all have seen an old pickup driving in front of us and it looks like the rear end is trying to catch up with the front. Will cause tire wear. Usually a bushing is worn or you have bent parts if this is out of spec.
SAI or Steering axis inclination (KPI King pin inclination) is the angle of the steering pivot line viewed from the front of the vehicle. If you have a mac phearson strut front suspension it is the angle the strut assembly sits at. This also aids in returning the steering wheel to center. If there is a big enough difference you can get some pulling at slower speeds but this also means something is bent, worn, or broken if it is off too much.
I wanted to cover the basics on the alignment sheets. On our Libertys nothing is adjustable in the rear. I am not sure what all is adjustable up front either. This is just to help people out when they bring their vehicle in. Now the biggest thing to remember is that an alignment problem will not cause a major pull. More often then not a tire is bad or you will have bent, broken or worn parts. Also it is desirable to have a vehicle that maybe drifts slightly to the right just in case you fall asleep or god forbid something else happens to you while your driving, hopefully your vehicle will drift towards the ditch and and not into oncoming traffic. Or for you guy that drive on the wrong side of the road
a vehicle that pulls left slightly. Here is a copy of someones alignment print out that I found online and hopefully you will be able to look at it now and know whats going one. Before I was taught any of this I sure as heck couldn't.
Cross camber and caster is the difference between the two side. You want these numbers as small as possible! .2 degrees or less if possible.
Included angle adds SAI and Camber together. If included angle has a large enough difference side to side again something is bent or broken.
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