What are all the terms in they talk
about when I get my car aligned?
Here is a description given by Milton3 [milton3@pobox.com] from the List.

If you go to a good shop with techs that understand what they are doing/why they are aligning the car - you should have no problem getting the car aligned.

Basically, have an alignment done to encourage the car to respond as you like, and protect against tire wear to fit your budget.

Here is a little alignment info to get you going:

TOE: This refers to the degree that the tires are parallel. A perfectly parallel pair of tires is said to have zero or neutral toe. Most manufacturers spec a slight toe-in (that is to say that they set up tires a little pigeon toed versus west-footed). This prevents tramlining (tires following grooves in road instead of steering inputs), and generally promotes under steer at turn-in. Neutral toe or slight toe-out will provide you with faster turn-in, but neutral tends to tramline and toe-out wears tires pretty quickly when combined with camber. I prefer neutral toe as it turns in fairly quickly, but it is much easier on the tire wear (read pocket) than a toe-out setup. I would set up a dedicated track car with neutral toe because fast turn-ins at speed can get hairy, or a dedicated autoX car with slight toe-out to get the car to turn quickly.

Camber: The degree to which the top of the tires lean in (/_\) or out (\_/) relative to the contact patch. When a car is turning, lateral forces work in concert with the downward gravitational force. So, by setting up a tire to lean in (negative camber), you are placing it in a state of readiness to best handle the lateral forces. Negative camber costs you tire wear (inside of the tires) when you spend too much time traveling straight. If you are attracted to twisties, a negative camber setup can actually prolong tire life - but few of us have that many twisties available. Manufacturers again tend toward slight positive camber to promote under steer.

Caster: This is the most difficult to explain. It is the degree to which camber is made more negative as the wheels are turned. Just realize that it is rarely adjustable, and the manufacturers set this one up for the type of ride. I.e., Mercedes is famous for very high caster. High caster is noticed primarily by how much the car tends to return to straight track following a turn. Low caster cars just keep turning - high caster cars auto center. As you can guess, high caster can substitute for negative camber to an extent. It is generally only adjustable by changing the suspension geometry radically.

So, the point of an alignment is to set optimal toe and camber given a fixed caster setting. And, you can make these determinations yourself. Toe figures are generally expressed as plus or minus a couple degrees, Camber figures can get a lot more radical and can extend to the tens of degrees, but are extremely radical and of questionable benefit past about 10 degrees.

My suggestion is zero toe and as much negative camber as is available by adjustment (probably 2 to 5 degrees tops, but I haven't looked at roadster alignment yet). Gives a quick, performance oriented response while not being too bad on tires as long as you remember to seek out the twisties often. If you are consistently heating up the inside of the tires more than the outside, you may want to dial the camber back.

Hope this helped. There are many places on the web that do a more thorough (i.e., with pictures) job of explaining suspension geometry issues. Don't hesitate to search, but if you get caught "stringing" your car for a self alignment - plan to spend all day the first time.

Milton

Here are a few recent alignment suggestions from the List:

I finally accepted my lack of front-end alignment skills and decided to have some professionals do it. I took the roadster today to Custom Alignment of Mountain View, CA and boy did they do a superb job. I tried to dial in negative camber myself, using with shims. I found out that I acheived only -.42 on the right and -1.2 on the left! The car pulled to the right, especially under hard braking. Caster wasn't nearly within each other. It was -.20 on the right and +1.20 on the left. Yikes! Toe was also a nightmare. -0.19 right and -0.12 left. Not to mention a loose steering wheel and some awkward turn in at high speeds.Custom Alignment setup the car according to my weight! Specs l/r: -1.5/-1.6 camber, caster +1.10/+1.20, and toe +0.03/+0.02. And the car handles great. Steering is firm and no more spookiness on turns.

I had Tetanus set up with 3 degrees negative camber, 2 degrees positive caster, and zero toe. That was on radial autocross tires. I could have set the toe out a little, but the worn out front suspension made it toe out during driving. I changed the camber to negative 1.5 and caster at positive 1.5 for the bias ply slicks I'm running now.

I would suggest 1 to 1.5 degrees negative camber, 1.5 degrees positive caster, and 1/8" toe in for a street car with radial tires. This will give fairly good steady state cornering, good straight line stability, and nice turn-in response.

For my dedicated autocross car I run: 3/16" toe out, -2 deg camber, -5 deg caster

For a street car I would not go more than  -1 camber over the long tern or the in side of the tire wears out too fast. Once you get the shims in place, you can figure the thickness and remove or add them in about 10 minutes per side in your garage to adjust your camber quickly.

Manufacturers tend toward slight negative camber. I've been involved in suspension design for over 10 years, and have done work for several auto manufacturers, and a few tire manufacturers as well. Most modern cars, trucks, and buses have some negative camber, or zero camber. Camber affects turn-in and tire wear, and a lot of work is done to try and optimize this tradeoff. You do see positive camber on older cars. The Hummvee originally had some positive camber on the road version, I think that's been redesigned. So there are a few exceptions.

My personal experiences with my street car:

I use just a little bit of toe-in on the race car for stability under braking. Camber was set at around 2.25 degrees, this was arrived on after a few discussions with my Avon tire engineer, and lot's of track testing which included measuring tire temps.