This handy tool produced by FinishLine makes adjusting rearend toe fast and easy. The tie
Step 4 - Once the right front (RF) wheel has been adjusted to point straight ahead parallel to the RR hub, level the RF laser (vertically) to shine the point on the floor. Rotate the RR laser so that its point shines next to the front laser point on the floor. This shows the alignment, side to side, of the tire contact patches, the beams being equal offset distances from the centers of the contact patches. Adjust the Panhard or J-bar length so that the right-side laser beams (tire contact patches) are one point. This means both right side tires are lined up.
As you adjust the rearend side to side, there is a possibility that the alignment will change as the rearend moves laterally. You must recheck to make sure the rearend is still perpendicular to the framerail each time you adjust it. This may take several tries to get both the rearend square and the right-side tire contract patches lined up.
When using the string, you must compensate for the camber of the right front wheel which moves that tire contact patch out. At the hub height, if you 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. Look at the chart to estimate how much to compensate for the camber. Subtract the compensation amount from the offset read at the RF wheel to find how far from the string the RR wheel needs to be in order to line up the right side tire contact patches.
When using the string method, set the string height at hub height and align the string wit
Step 5 - It's time to set the static toe at the front wheels. You can use toe plates to do this. Remember to be careful and accurate and do the measurements several times to be sure of the numbers. Adjust the left-side tie rod to set your toe. Leave the right side alone.
Using the laser, at the left front (LF) hub, align the left-side targets with the LF laser at the front and rear and at 14 feet (168 inches) from the LF hub center. Measure the distance between the front targets and then between the rear targets. The difference in distance will reveal the amount of toe present in the front wheels.
To get the exact toe amount at the tire, first divide the front-to-rear difference by the distance between the targets (front-to-rear) of 336 (two times the 168 inches). This is the toe amount that exists in one inch. Then, multiply this number by the diameter of the tire (tire circumference divided by Pi or 3.1416). On an 85-inch tire, this diameter is 27.05 inches. Multiply the toe-per-inch by the tire diameter and you have the amount of toe in the front end.
Adjust the toe settings so that you have the desired amount of static toe in the front end. If you started out with the LF wheel straight ahead, dialing in 1/8 inch of toe at the tire will require about 3/4 inch of movement of the laser point at the front target. If you adjust your left side tie rod so that the difference in distance between the front and rear targets is 1 1/2 inches, you will have 1/8 inch of toe.
Step 6 - It is now time to measure for the amount of Ackermann present in the steering system. This can only be done accurately with the laser system. The analog method would have you use toe plates with degrees marked on them. These plates, as you will soon see, are not accurate enough for this measurement.
Make sure the laser or string line is parallel to the framerail.
With both front lasers pointed ahead, line up both targets so that the points are exactly on the centerlines. Turn the wheel the approximate amount that the driver does when negotiating the turns at the racetrack. Take the rear targets and place them 14 feet in front of the front hubs, and line up the centerlines with the laser points.
Measure between the two target centerlines on each side. The difference in distance between pairs of targets is now divided by 168 and multiplied by the tire diameter to find the Ackermann toe that is added to the static toe settings. The number should be low, around 1/64 inch of added toe for a half-mile track. This would be around 3/32 inch difference in the amount that each wheel turned (LF turning more than the RF), measured on the targets or 0.097 in decimal inches.
For a tight, quarter-mile track, the added toe due to Ackermann effect should be about 1/16 inch, or about 3/8 inch difference at the targets. Toe plates that might slip slightly cannot come near the amount of accuracy required when dealing with fractions of a degree.
This entire process should take only about an hour or two if there are several team members helping. That is little effort expended to make sure your car will track correctly and that misalignment will not interfere with performance. Repeat this entire process often, especially after kissing the wall or being involved in a crash. Once you're convinced your car is aligned, you can concentrate on the other important aspects of your chassis setup.
(Special thanks to Mike and Kristal Loescher)
By using a tool that is a carpenter's square that has been cut to fit against the framerai
This is what you should end up with after aligning the rear to the right-side tire contact
The tire contact patch is offset from the center of the wheel at hub height when you add n