When making marks on the shop...
When making marks on the shop floor, you can use wide masking tape and a Sharpie fine point pen. This helps keep the floor surface clean and provides a very good surface for making lines and labeling the marks. Make sure your tape is straight and level when making these measurements. Don't concentrate so hard on the numbers that you miss that the tape is bent around a jackstand chassis support.
With the string method, run a string down each side of the car at hub height and parallel to the centerline you have established. Then, simply measure to the side walls or wheel rim of each front tire with the tape measure and make both front and rear measurements equal by adjusting the tie-rod lengths. We can set our race toe later on after we have aligned the car.
Step 4 Right-side tire contact Patch Alignment Once the front wheels have been adjusted to point straight ahead and parallel to the centerline, we need to align the right-side tire contact patches. We do this by using our laser systems as described in the user manuals for each system.
Adjust the Panhard or J-bar length so that the right-side tire contact patches are inline, or if your desire is to offset these, set the desired amount. This means that we will either have both right-side tires lined up or at least know what our offset is. For stock classes using rear suspensions that are not adjustable, you will need to run different offset wheels to achieve right side tire alignment.
When using the string method, we need to compensate for the camber of the wheels which moves the tire contact patches out. At the hub height, if we line up the tire sidewalls, the RF tire contact patch will be outside that line due to the negative camber present in the RF wheel. The rear wheel may also have camber due to a cambered rearend or just the stagger. Look at the chart to estimate how much to compensate for the cambers. Subtract the compensation amount from the offset read at the wheels to find how far from the string the wheels need to be in order to line up the right-side tire contact patches.
This is what we should end...
This is what we should end up with after aligning the rear to the right-side tire contact patches. Measurement points 5 should be equal. Once the rearend has been aligned perpendicular to the chassis centerline and the right-side tire contact patches lined up, we will deal with the front toe and Ackermann issues.
As we adjust the rearend side-to-side, there's a possibility that the rearend alignment will change as the rearend moves laterally. That's why we do the right-side alignment first. We'll now need to check to make sure the rearend is perpendicular to the chassis centerline and if not, adjust it.
Step 5 Rearend Alignment Once the right-side tire contact patch alignment has been done, we can then square the rearend. The rearend should always be set perpendicular to the centerline of the car. We do this with the strings by creating a line that is perpendicular to the centerline we have already established. Using a simple 3-4-5 right triangle with the lengths doubled, we can measure off the centerline to establish our line to measure to the rearend.
When using the laser systems, follow the manufacturer's guidelines for doing that. The lasers will accurately measure the alignment referencing the chassis centerline.
Step 6 Ackermann Measurement It's now time to measure for the amount of Ackermann present in the steering system. This is best done accurately with the laser systems. However, the "analog" method using strings can also tell us whether we have unwanted Ackermann or not.
If using a laser system, follow the manufacturer's suggestions and recommendations for measuring for Ackermann. If you don't have a laser system, you can use strings. Here's how you do it.
Start by pointing the front wheels straight ahead. Pull a string along the outside of the tires at the tire bulge at about the spindle-pin height (avoid the lettering areas). Project the line out to the front of the car 10 feet and make a mark on the floor with the string aligned with the sidewall (I use a piece of wide masking tape and a Sharpie marker). Do this for each front tire.
Then, turn the steering wheel about the same amount it's turned on the track when you're going through the turns. Again, string the front tires and make marks at 10 feet out in front. The distance between the two marks for each wheel should be the same for the left front wheel and the right front wheel if there is no Ackermann present. If those distances are different, there is some amount of Ackermann or Reverse Ackermann present.