Once a tire shop messed up the toe in alignment on my car so bad my new front tires wore out in 5000 miles. Another time I took the car back because the steering wheel was off by 15 degrees when I went straight down the road. After hitting a really big pot hole, I have wanted to check if I took some damage before I mess up my tires.
Do not make adjustments to the alignment/steering of any car. If you mess it up you could kill the driver, passengers, occupants of other cars, pedestrians, bushes and small trees. Leave this to the professionals. It never hurts to check that they did a good job or to see if you need an alignment to begin with.
What is toe alignment on a car?
See picture. If the front tires are aligned so that they point in like a person who is pigeon toed that is called Toe IN. If the tires point out that is called Toe OUT. If the toe is not adjusted within specification the car can miss-handle in turns and the tires will wear faster. The specification is same for a model of car but different models have different toe specifications. The spec is given in the shop manual and may be found on line. The toe specification of the Ford F150 in this example is a toe in of 0.06 degrees plus or minus 0.25 degrees so ideally you would like to have a gauge with an accuracy better than 0.05 degrees.
Check that steering and suspension components are not sloppy and over their wear limit. A system that is too sloppy cannot be aligned. Learn how to diagnose worn out parts. I have replaced ball joints, idler arms, pitman arms, shocks and tie rods before an alignment. I have also been told that I need to replace perfectly good components.
How to measure toe:
Step 1:Lean the stick with a mirror against the left car wheel. The discs touch the wheel rim and the stick is level. See picture.(Note that the mirror bracket does not rotate on the stick. The stick rotates in the discs touching the car wheel rim.)
Step 2:Adjust the laser alignment so that the beam hits the mirror and bounces back to the zero mark on the target paper. Do not adjust the laser alignment after this point.
Step 3.Move the stick with the mirror to the right wheel.
Step 4.Read the toe result in degrees on the target paper.
Construction is pretty straightforward. I chose a laser that I could power with a wall wart and could mount in an aluminum heat sink. Most laser pointers have a 30 second duty cycle due to poor heat sinks but will work for a while. The base and bracket that hold the laser allow easy adjustment of laser height from the floor as well as pitch an yaw. I used a carbon fiber arrow shaft as the stick that holds the mirror and discs.
Note that the angle on the gauge is twice the toe angle. To see this, adjust the wheel so that it has a toe in of 45 degrees. See drawing to note that the angle between the beam hitting the mirror and leaving the mirror is 90 degrees. To label the target paper for a toe in of 1 degree, calculate the beam displacement for the return beam for 2 degrees but label the target 1 degree.
Of all the components, the build only has two matched discs that require some care during fabrication. I designed the discs that touch the wheel rim so that I could chuck each disc on a step allowing the center hole and outer diameter surface to be completed in one setup for both discs. I cut the OD on both discs without moving the cross slide on the lathe so that the diameters match. I also used a center drill to ensure that the hole was concentric. To check the quality when the discs were completed, I put the discs on the shaft and the arrow shaft in the lathe chuck. The cutting tool was replaced with an indicator to measure the eccentricity and shake as I turned the discs about the shaft by hand. The fit between the arrow shaft and disc hole has a clearance of less than 0.001 inch. A 0.001 inch eccentricity or a 0.002 inch difference in OD sizes of the discs will cause an error of 0.01 degrees toe...Read more »