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Do-It-Yourself Car Alignment

There are many books which discuss easy home methods for checking alignment. If you're at all interested in this sort of thing, you should really get a copy of Fred Puhn's How to Make Your Car Handle — it's a great book and covers a lot of useful techniques as well as theory of suspension design.

Josh warned us: When doing this, you must know beforehand whether your vehicle can handle a zero toe-in. My first generation Neon ACR had no problem with zero toe-in, but when I hit a major bump in my 2001 Sebring Sedan after setting it to zero toe-in, I came close to losing control of the car. Every tiny bump produced a resounding loud “pop” in the suspension, though everything was new. Setting the toe-in to +1° cured both issues.

But here's a really easy, fast, two-person way to check toe. I use this on my X1/9, which hasn't seen a professional alignment rack since I bought it, and since I race it very actively, I consider proper alignment very important, but I don't want to spend $80 every time I make some kind of minor change to the suspension just to save myself about five minutes of work (30 seconds to check, a couple minutes to change it if it's wrong, another 30 seconds to recheck).

  1. Drive the car to a level parking place. Ideally you want the car loaded as it will be when it is driven (e.g. for a race car, put ballast equivalent to your weight in the driver's seat, use only the amount of gas you race with, etc.) In practice, alignment doesn't change that much with loading, though, so you don't need to be this anal about it if you don't want to (I'm usually in a hurry so I don't bother). However, it's important that you drive the car straight forward to the place where it will be aligned -- once you turn the wheel, or jack the car up and then set it down again, you've changed the static alignment and the numbers you measure will be wrong.
  2. (This part I got from Brad Martinson, and it's a really neat hack.) Get two straight pins and stick one into each front (or rear, if you're checking rear alignment) tire on the front of the tire at some constant height H above the ground. H should be lower than the ground clearance of your car in the neighborhood of the wheels.
  3. Have a friend hold one end of a tape measure against the tire starting at one pin. You stand on the other side of the car, pull the tape measure so that there's no slack and measure to the other pin.
  4. Roll the car back (not forward, you'll roll over the pins!) until the pins now stick out the back end of the tires and are again at height H.
  5. With friend, again measure between the pins.
  6. The difference between these measurements is your toe.

You don't need pins (in fact, I seldom use them) as long as you can pick a repeatable place on the tread from which to measure (it depends on the tread pattern) Note: chalk marks should work nicely. An easy way to make sure H is constant is to use a piece of 2x4 as a marker (4" seems to be a good height on a lowered X1/9; on most cars you could probably measure somewhat higher). Measure as high as you can, because you get better accuracy that way (the tire sticks out more higher up, so you're measuring bigger numbers and your error is a smaller percentage).

In practice, 1/32" is plenty of accuracy for measuring toe (you don't really know precisely what your front toe should measure to better than 1/32", do you? I sure don't, and I've been experimenting with my car's handling for three years. Optimal settings change according to tire compound, my mood, wear in the suspension bushings, how cold and wet the weather is, etc.).

If you want a bit more accuracy, then put the car on alignment plates. Get four thin squares (about 6"x6"x3/16", say) of some smooth metal, like aluminum. Use them to make two sandwiches of metal outside, oil or grease inside. Now put one sandwich under each tire. Now you have an alignment plate just like the professionals use (only a lot cheaper) and you can turn the wheel, move the car, etc. without screwing up your static toe measurement. You can't use pins or roll the car back any more, though.

One-person toe measurement:

This is considerably more hassle, but there are several ways to do it. You can set up two strings parallel to each other and to each car's centerline, and measure from the strings to the front and back edges of your wheels. (Setting up the strings takes from 20 minutes to over an hour; once they're set up, checking the toe takes about one minute to do all four wheels, unless you trip over the strings, in which case you have to set them up all over again.) I hate this method.

A method I like better is to drop a vertical (using a plumb-bob) from the centerline of the front and rear of each tire (do the rear, too, while you're at it. Yeah, even if it's non-adjustable -- might as well check it, because this will tell you whether your frame is straight, so it's a good thing to do on a new car). Make a mark on the floor of the garage below each tire centerline. Now drive the car away and draw lines all over the place and measure all of them: you can get front track, rear track, right and left wheelbase, front and rear toe, and diagonals between the tire centerpoints. Comparing things like the diagonals and the right/ left track will tell you how straight your frame is.

Cheap and easy camber measurement:

I've tried a few camber gauges but I find them more difficult to use than this method. (I think there are easy-to-use gauges, I just haven't seen one).

If you're measuring camber with the intention of changing it if it's wrong, do it BEFORE you measure toe -- on most cars, changing camber will also change toe.

Get a carpenter's level. You want one which is slightly shorter than your wheel size (e.g. on my 13" rims a 12" level works okay). Rest the bottom of the level against some repeatable part of the wheel (like the bottom of the outside edge of the rim, but you'll need different techniques with some wheels). Now swing the level (without losing contact with the wheel) until it's exactly vertical. Using a caliper (you can use a ruler, but a caliper is much easier) measure the distance from the level to the wheel. Now you have your camber in inches. Some trigonometry can give you the camber in degrees, if that's what you want.

There are lots of variations on this -- you can use a coarse-thread screw instead of a caliper, and count turns. You can use a dial indicator instead of a caliper. You can make a gizmo with sliding fingers that stick out from the level and contact the wheel at just the right points for your size wheel. You can just hold the level against the wheel and make calibration marks on the window where the bubble appears. You can use a vertical from the floor and measure from there to the bottom and top of the wheels, then subtract. Whatever seems easiest for you.

Jim Muller follows through:

Akkana gave us a nice description of practical ways to do alignment. This is a short followup to that.

She suggested sticking pins in the tires at some arbitrary height in the tires. (No, of course you don't want to stick pins all the way into the tread. That might let the air out, much akin to letting the smoke out of your electrical system. So I'm not going to talk about that.)

Toe-in is supposed to be the difference between the front and rear of the tires (tyres), measured at the axle center (centre). Let us assume zero camber (cambre), meaning the axle is exactly horizontal (an admittedly weak assumption, but not a problem for our purposes).

      .                     .
      .A ------- O ------- B.
      |.                   .|
      |  .C             D.  |
      |     .    E    .     |
      |         ...         |
      -----------------------
      <---------d----------->

Ideally the toe-in should be measured at the two points a distance d apart, where d is the tire (tyre) diameter (diametre). [All this English spelling is getting to be a problem!] This would mean using points A and B. However had you used point C instead of point A, then the distance between the tires (tyres) would be different by some small amount. (Well, if you really want to know, the total distance you should see at each point will be

track + sin(toe-angle) * sin(rotation-angle) * diameter

where track is measured at E and rotation-angle is measured from vertical, as in the angle EOC. Camber adds more terms, but we can still ignore it.)

For zero toe-in, all this would make no difference, since the distance between the wheels will be constant for all points A-E. However, for non-zero toe-in, if you measure it at C (and D) instead of A and B, you'll get a smaller value, and thus are likely to set toe-in to be larger than it ought to be. ("Smaller" and "larger" are used here in an absolute-value sense.)

Now, this is not a *serious* problem, and almost none at all if you are going for zero toe-in. The reason it isn't so serious (and also the reason we can ignore camber) is that the errors this produces are quite small compared to the accurace you really need. In other words, you don't need to be exactly at A and B, and anyway, you need to work at some point that has clearance around the body and frame. But the closer you can get to the height of the axle, the better your results will be, with increasing importance for desired toe-in further from zero (either positive or negative).

If you do have to work at some height significantly removed from axle height, you could compensate. Use an rotation-angle that is symmetric front to rear, and figure that your measured toe-in will be reduced from what it "really" is by a factor of

2 * d * sin(rotation-angle).

Even for desired zero toe-in, measuring at C and D reduces the precision of your measurments. So it is best if you work as close as possible to axle height.

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