Tire Alignment
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Tire Alignment is something every car owner has to deal with - if they want decent tire wear and a car that drives where you want it to instead of where it wants to, that is. For most folks it's as simple as stopping by the local alignment shop once every year or so and getting things put back into whack again. For the true gearhead, it has greater implications and becomes something that you really need to understand better and know the basics about to really do what you want to do with your car. My goal with this page is to give you a basic idea about what you should care about when doing the type of work that a typical "I'm working on my own car" sort of guy would encounter - and what to do when you encounter these things. I'm not trying to be an authoritative source for all things alignment-related. Entire books have been written about the details of how a suspension reacts in real-life situations, and the final alignment of all the parts is critical to making it react in a sane and predictable manner that you would consider "safe" to drive. This page barely scratches the surface of the depth of knowledge on this topic, but it should be enough for you to learn about this and manage to get your car down to the alignment shop without killing anyone or destroying your tires.

The suspension in a automobile is a fairly complicated pile of parts to really wrap your mind around, but getting a basic understanding of the major adjustments and their effects is pretty simple, and will give you something to work from when you have to deal with these things yourself. That basic understanding is very helpful in many common situations such as when replacing parts and you need to get things close enough to drive to the alignment shop without tearing up your tires, or when trying to make a slightly different adjustment from what the factory says, or simply making sure that you're speaking the same language as the guy doing the actual alignment on your car down at the local alignment shop. No Car Guy worth his motor oil would dare let the mechanic know more than he does, and alignments are no exception. Car Craft even did an article on this, so it can't be that scary, now can it?

If this page hasn't given you enough details, there are a ton of great web pages out there. Google for "caster camber explained" as a starting point and perhaps "caster camber race" and go where you may from there to learn all about this.


Custom Alignments

Why would you even want to use "custom" alignment settings that deviate from the factory settings? One situation is when you have replaced major pieces of the front suspension for anything from a simple replacement of a "bad part", up through putting in new bushings, to an entire new front end as part of a brake swap, the issue of tire alignment becomes more complicated and personal - how do you drive the car to the alignment shop before it's aligned? Other situations revolve around the need or desire to use non-OEM alignment settings. What if your car was originally equipped with bias ply tires and you want to switch to radial tires? Some cars require different alignment settings - like my 1958 Buick Special. Another common case is if you want to use your car for somewhat non-standard uses such as drag racing or road course driving. Specialized vehicle uses can often benefit from custom alignment settings to get the best performance possible. As an example, when drag racing, the car spends it's most important time accelerating under power, and as such you should do the alignment with the front end jacked up an inch or more so that the alignment settings are most correct when the car is accelerating down the drag strip. Another example is in road racing, where more positive caster will help the car track straighter and not wander, but it increases steering effort. Or in oval track racing where you only make left turns and it's common to put more positive caster on the right front tire than the left to help "pull" the car down into the turn and stay "hooked up" through the turn.

There are lots of good reasons to want to do non-standard things with your alignment, and if you think you have a need to do this, then it might be an OK thing to do. Just be sure to research your desired settings before you perform the work on your car and be sure to proceed carefully when first driving the car again after changing things about. Cars can react strangely when aligned in certain ways, so beware. You are off into strictly "at your own risk" territory if you do this sort of stuff!


Front End Alignment

Here are details on doing an alignment from the 1976 Chrysler Shop Manual. This has some good details on the theory involved, and a chart that explains the various terms used to describe the alignment - camber, caster, and toe-in. It also has the basic process for doing an alignment - the order in which you adjust stuff matters a lot because adjusting one thing tends to affect the others.

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Here are the details on doing an alignment from the 1974 Buick Shop Manual. This has good details on how changing the adjustment at the front and rear mounting points for the upper A-arm affect camber and caster - this is critical information to understand so you know what the basic effects are of changing the adjustments in each place.

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Rear End Alignment

The rear of the car can be measured like the front, though on most muscle-car era vehicles the adjustments are limited to making sure the axle is installed square to the centerline of the car. Many more modern vehicles and pretty much any vehicle with an independent rear suspension will have multiple adjustments for the rear wheels the same as the front, and they are just as critical to get set correctly. If your vehicle does have adjustments in the rear, make sure your alignment shop does a full "4 wheel" alignment, not just a simple "2 wheel" alignment. More expensive, but worth it. If your car does not have rear end adjustments (at least any that don't involve cutting and welding :-), then make sure that the alignment shop checks the alignment of the rear wheels against the front, and assuming all is reasonably square to the car, that they perform what is called a "thrust alignment".

What's a "thrust alignment"? It's where they do the front end adjustments based on the actual measured thrust angle of the rear wheels. What's a "thrust angle"? The "thrust angle" is the angle that the rear axle in a traditional rear wheel drive car is set to relative to the centerline of the car. For whatever reason, sometimes the rear axle is not perfectly in line with the body of the car and it is actually pointed a degree or so to one side or the other. That misalignment is called the "thrust angle" - aka, the line that the rear axle actually puts thrust (power) to the pavement on. If you can't get all four wheels in perfect alignment, the next best thing is to at least have all four wheels pointed in the same direction, even if the front and rear wheels are not in the same exact "line". As long as the back end is pretty close to square, aligning the front wheels to the actual angle of the back wheels results in a much improved alignment - the front and back tires don't fight with each other all the time and they will go in the same direction. In extreme cases, it results in a car that goes down the road at a strange angle where the wheels are visibly out of line with each other. The diagram below illustrates this in an extremely way.

ThrustAngle.jpg (18483 bytes)



This is the fun part - how can you measure this stuff reasonably at home? The alignment shop you go to probably use (or more correctly, ought to be using!) a large drive-on lift hooked up to a computer with cool and expensive looking sensors that clamp to each wheel. You can't possibly duplicate that at home, can you? Actually, you can, but you need some specialized tools, and lots of patience. For most of us, we want to get things "close enough" to get down to the real alignment shop, and perhaps tinker with things a bit once we know where they started at. Harbor Freight sells a Strut Alignment Level (item #42496) and Wheel Alignment Gauge (item #30167) will allow you do to basic measurements of camber and toe yourself. As of right now I do not know of an easy way to check caster at home, though if I do, I'll update this page. For the record, there are ways to do this without high-dollar computerized alignment machines, but they involve some non-trivial math and very careful measuring with various tools. It's not something that I would consider easy, and most folks would be scratching their heads and looking confused from just reading about how to do it, let alone actually attempting to do the measurements involved. For the level of expertise I am targeting with this article, I believe you really only need these two basic tools.

For lots more ideas on custom building tools, and making very precise measurements with very simple tools (like some string, a ruler, and a pair of jack stands) start Googling for stuff like "home alignment" and "measuring camber at home" and start reading up on all the details you can find. As I mentioned above, there are lots of details out there if you want to learn, and the actual process is pretty simple, it's just a bit tedious and something that requires you to be very precise to get a proper result. One site I read advised that the first time the person did this work himself it took him 6 hours to get it to the point he was happy, and now he could do it again in 3 hours. Your mileage may vary.

Comments? Kudos? Got some parts you'd like to buy/sell/barter/swap? Nasty comments about my web page so far? You can email Mike or Debbie.

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Page last updated 01/02/2009 01:51:39 PM