The True Laser Track System...
The True Laser Track System sends a single laser beam to the ground and to targets placed at the front and rear of the car. The system can check wheelbase, alignment, Ackermann, toe, and more.
Step 2: System-to-Frame Setup Once the rear wheels have been toed straight-ahead, square the laser system to the frame. Most car builders will align at least one framerail parallel to the intended centerline of the chassis. It may be located on the right side or as the weight box on the left side, next to the driver. You can also align the laser system to the centers between the front and rear clip rails closest to the main framerails.
This setup can also be done using strings. We will set up a "box" with strings on each side and at the front and rear. We use plumb bobs to make marks on the floor off the outside of the framerails or the front and rear clip rails. For perimeter cars, or cars with no offset in the chassis, we can split the measurement between the clip rails to find the centerline of the chassis.
For offset chassis, we could use a straight rail or we could split the clip rails. Measuring between the marks, we can split the distance in half and place a mark at the halfway point, or at the centerline of the car.
The Real Square(tm) Alignment...
The Real Square(tm) Alignment System uses scaled bars attached to a fixture that bolts directly to the hub. After the lasers are set up and aligned with the chassis, the wheel alignment and toe can be read on the scaled bars. Ackermann can also be checked with this system, along with other parameters.
Step 3: Center the Steering Box Center the front steering rack by turning the steering wheel lock-to-lock and back half the number of turns from full lock in either direction. Once mid-rack (or mid-box with drag link steering) is found, lock the steering shaft with two vise-grip pliers.
We want to make sure the steering is centered and the wheels are pointed straight-ahead. Once the steering box has been set to center, adjust each tie rod so that the right and left wheels are pointing straight-ahead. With the laser systems, this is done quickly and accurately.
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 sidewalls of each front tire with the tape measure, and make both front and rear sidewall measurements of each front tire equal by adjusting the tie-rod length. We can set our race toe 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 their user manuals.
Adjust the Panhard or J-bar length so that the right-side tire contact patches are in line, or if your desire is to offset these, set the desired amount. This means that we either have both right-side tires lined up or at least know what our offset is.
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 sidewall, 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 set into it. 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.
The offset to the frame measurement...
The offset to the frame measurement can be taken by using a laser or a string. The string is a must for a low-budget team, but the laser systems are much more accurate and do more alignment tasks in less time.
As we adjust the rear end side to side, there is a possibility that the rear-end alignment will change as the rear end moves laterally. That is why we do the right-side alignment first. We will now need to check to make sure the rear end is perpendicular to the chassis centerline and if not, adjust it.
Step 5: Rear-end Alignment Once the right-side tire contact patch alignment has been completed, we can then square the rear end. The rear end should always be set perpendicular to the centerline of the car as well as to the right-side tire contact patches.
We do this 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 rear end.
Step 6: Setting Front Toe It's time to set the static toe at the front wheels. We can use toe plates to do this. Remember to be careful and accurate, and measure several times to be sure of the numbers. Adjust the left-side tie rod to set your toe. Leave the right side alone.
Roll the car and recheck the toe setting. Remember that for toe-out, the front measurement will always be more than the rear measurement. If you are using a string or laser, as opposed to toe plates, to check your toe-out, the opposite is true. The front measurement from the laser/string would be less than the rear measurement. I know a crew chief who got this backward too many times.
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. Measurements "a" and "b" should be equal, as well as dimensions "c" and "d."Once the rear end has been toed straight-ahead, aligned perpendicular to the chassis centerline, and the right-side tire contract patches are lined up, we will deal with the front toe and Ackermann issues.
Step 7: Ackermann Measurement It is now time to measure for the amount of Ackermann in the steering system. This is best done accurately with the laser system. However, the analog method would use strings and 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 do not have a laser system, you can use strings. Here is 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. Go 10 feet in front of the car and make a mark on the floor, with the string aligned with the sidewall (I use a piece of wide masking tape and a permanent marker). Do this for each front tire.
Then, turn the steering wheel about the same amount it is 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 of the car. 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.
The tire contact patch is...
The tire contact patch is offset from the center of the wheel at hub height when we add camber to a wheel. The chart shows how far offset the contact patch center is related to the wheel center at hub height.
A greater measurement on the left indicates Ackermann (gain in toe-out), and a greater measurement on the right indicates reverse Ackermann (loss of toe-out). A 1-inch difference equals about 1/4 inch of Ackermann, or added/loss of toe. So, if you can get your differences to around 1/4 inch (where the left side is more), you should be good to go. A recent car we checked had a 3-inch difference, or almost 3/4 inch of added toe in the turns. That's way too much.
Conclusion This whole process of aligning your car should take only about an hour or two if there are several team members helping. That is very little effort expended to make sure your car will track correctly and that misalignment will not interfere with your car's performance.
Repeat this entire process often, especially after kissing the wall or being involved in a crash. Once you are convinced that your car is aligned, you can then concentrate on the other important aspects of your chassis setup.
Here, we see the layout for the process of setting up to square the rear end. Note that the lines formed by the intersecting marks are right triangles. Take your time and measure very accurately. Remeasure if you feel that everything is not right once you pull the rear string line across the outer points of the triangles.
Laser systems are the best tools to use to check for the presence of Ackermann. If you do not have one of those, you can use strings to project the alignment of each wheel out in front of the car.