Basically what I’m doing
is placing a laser level against the outer edge of each of
the front rims and letting the projection fall on a surface
that is relatively close (4 feet) and then moving that
surface to a point farther away (7 feet) and marking the
projection again.
I use a 2X4 board
propped up on two stools as the surface and I mark the
pinpoint beam projection (The red dots). I used a single
board. I actually moved the car backwards instead of the
board forward.
You don’t have to worry
about getting the boards (or board) in the correct
position laterally because you will be subtracting one
dimension from the other and dividing by two to get the
average. Just keep your marks straight
(which are the close measurements and which are the far
measurements). If you were interested in comparing the toe
in specifically on each side then you can use the laser beam
positioned on the rear wheels as a means to get the board(s)
in line laterally for each measurement.
My "a" dimension turned
out to be 1.3125" and the distance "b"
was 4' or 48 inches. So the toe in was the Arctan(1.3125
/ 48)=1.556 degrees (Way to big)
The Arctan is sometimes
displayed on your calculator as TAN-1
To get the toe in measurement as
defined by the manual which is the distance the front
edge of the tire is actually inboard from the back edge
of the tire.
Sorry more Trigonometry!
You just need to use the angle just
calculated and solve the equation for "a"
using 25" as the "b" dimension" (My
tire was around 25" in diameter)
a=Tan(A) X b
In My case 0.68" Which is way
out of spec! it should be around 1/16"
- 1/8". I turned the adjuster rod on my front
end about 2 turns and I ended up with a measurement of
about 0.448 degrees (or 0.19" on a 25"
diameter tire)
Here you can see that I needed to
tape a couple of blocks (Purple)
under the level to get it away from the wheel
to clear the spokes
and tire. These blocks have to be closely
matched in thickness.
The tape just serves to loosely hold the blocks in
between the level
and wheel rim surface.
You can see that the blocks are
rotated slightly so that I can bear the
clamping force against
the outer rim and get a repeatable measurement
Here you can "Barely" see
the projected laser
beam on my piece of wood sitting on the stool
