REPAIRS PAGE 84
WHEEL ALIGNMENT
Authors: Jan Vandenbrande and Mark Sirota. All articles may be distributed
freely and copied (unless otherwise stated) as long as the original authors or
origin are identified if available. Subject: Checking Alignment yourself. Well
this is one way to do it at home. Note that the accuracy is not great, it just
lets you know whether you are in the right ball park.
Camber:
1) Put the car on a level smooth surface (at least level sideways if not see
later). Bounce the car up and down and let the shocks settle in. (NB: Tires
should be pointing straight ahead)
2) Use a plumb bob (you know the string with the bullet like weight on the
bottom) and suspend it such that it goes across your L/F fender, passing through
the center line of your front axle. (You can also use a big precision metal
square (L-shaped thing at 90degr) or a combination of both).
3) Measure the distance from the string to the edge of your rim for both the
top and bottom parts. Don't mix the two numbers.
4) Do the same for the other tire.
5) Roll your car so that the tires rotate 180 degr, and repeat the
measurements. Take the average for each set of measurements. This takes care of
the error caused by bent rims.
6) If the floor is not perfectly level, turn the car 180 degrees (not upside
down :-|), and repeat the entire procedure for both sides, and take the average
of all numbers.
7) Now sit down and measure the distance between the two points you used to
take these measurements.
8) Sit down somewhere, dust off your old calculator, and calculate the angle
of the triangle formed by the string and the distance to the top part of the rim
(actually you have two equi-angular triangles). Dig up your high school trig
book.
The angle is considered negative if the top part is further away from the
string (i.e. top pointing inwards). The accuracy of your result is somewhere
around 1/2 degree, not great, but if you get angles of the order of several
degrees, you may have a problem.
See your manuals for the correct camber settings.
Toe:
I haven't done it this way, but this should work (or at least let you know
whether you are in the right range)
1} Start with a level smooth floor, bounce, tires straight ahead, etc.
2) Take a large square (L thing again), and measure equidistantly (to clear
the tire) from the front and rear side of the rim with one side of the square on
the floor and make a mark for each on the floor. Do this for both sides.
3) Now measure the distance between the L/R fronts & L/R rear dots on the
floor.
4) Roll the car so that the tires rotate 180 degrees, repeat and average out
the two measurement.
5) Do the trig thing again. Actually, what you are interested in is the
difference in angle between the toe of L and R with respect to the forward
direction. Note that some shops don't give the toe in degrees but rather in inch
or cm.
There are tools to do some of these things (like this bubble thing to measure
the camber) but they are probably too pricey for the casual user. I can imagine
that there are several more schemes of measuring things, all probably requiring
more sophisticated tools (which you could make yourself).
Concerning the accuracy of those machines in the shop... Hmmmm, sometimes I
wonder as they are not too gentle with them. And do you trust the high school
drop-out that failed maths doing the alignment for you? If you complain to them
(afterwards), the excuse is usually: "Sorry, must have hit a bump or a curb".
If you find any fault in any of the above methods or have some better ways,
let me know. Jan
Mark Sirota
Alignment
Another easy way to measure to is, first, get an accurate tape measure at
least as wide as the car.
1) Start with a level smooth floor, bounce, tires straight ahead, etc. This
is always important... Now, using the tape measure, measure the distance from a
groove in the tire tread on the left to the symmetrically identical one on the
right, at the front edge of the tire. Do the same for the rear edge of the tire.
(Note that you are assumed to have identical tires on the left and right. If you
don't, you should, for other reasons)
Using that trig text you just dug out, calculate the angle of toe determined
by the sides of your trapezoid. Note that this only gives you the total toe, not
the individual figures for each side. That means that even if you set your front
wheels parallel, they may not be parallel to the rears... The technique for
checking that is as follows. (This technique can also be used as a more accurate
way of measuring toe, and gives you individual readings for each side.)
1) Start with a level smooth floor, bounce, tires straight ahead, etc. Now,
using a plumb bob or some other such device, mark two point on the floor
directly under the center of the car, one near the front, one near the back.
There should be enough points under the car that are clearly under the center.
Draw a line between your two points. This line marks the centerline of the car.
Now, draw two more lines parallel and equidistant from the centerline, a couple
of inches outside the tires.
Set jackstands or some similar device directly on one of the outer lines, and
tie a string between them. Try to make sure the string is parallel to and
directly over the line on the floor, and it should be at the height of the
center of the wheels. Measure the distance from the string to the wheels, at the
front and at the back edge of the wheel. Use a square to make sure you measure
perpendicular to the string.
You should find that the average distance of each front wheel from the string
is equal, and that the average distance of each rear wheel from the string is
equal.
These sorts of descriptions are hard in text; a picture would be worth a
thousand words. I seem to remember an article on this in VW and Porsche or
Auto-X or Sports Car a few months ago... Anyone else remember that? Maybe I can
dig up the issue and let you know, so you can find it at your library or
something.
I have seen toe and camber measuring devices sold by Hand's Solo, which are
$40 to $50 a piece. The toe device only gives total toe.
I have also seen a handmade toe device, which acts similarly to the tape
measure method I described above. It was a very long rod with calibrations and
slidable, lockable pointers on it. You would stick the pointers into the tread
on the tires at the front edge, and lock their position on the bar. Then, you
would do the same at the rear edge of the tire, and note the difference.
You could slide the pointers along the bar, and lock them in position with a
thumbscrew. The bar had graduations along it so you could see exactly how far
apart the pointers were. This is much more unwieldy than the tape measure, and
probably not a whole lot more accurate.
Mark
Alignment after front end work
From: Mark Shaw
I no longer bother to mark anything after changing front end parts or struts
--I just re-align the wheels myself. Before I got a tool for camber measurement
($90) I used to use some shims and a simple 12" carpenter's square with a bubble
level in one leg:
1) Make sure the car is on level ground and roll it forward and back at least
one revolution of the tires.
2) Loosen, but do not remove, both the top (eccentric) and bottom (clamp)
bolts at the bottom of the strut to be adjusted.
3) Place the square with the bubble level horizontal and one end resting
against the lower wheel rim and the other end resting against the upper edge of
the wheel rim. Note that the contact points do not have to be on opposite sides
of the rim, just one point above the other on the rim edge and in a near
vertical line.
4) Now pivot the square away from the upper rim (or lower) contact point
while keeping the other end touching the rim until the bubble in the level is
centered.
5) Use small shims to fill the space between the end that is away from the
rim.
6) Measure the thickness of the shims and convert to degrees (each 1/16 inch
is equivalent to 0.3 degree of angle when using a square that is 12 inches long.
(or 1 degree = 0.2 inches)
7) If the gap between the rim and the square is at the top - you have
negative camber and if at the bottom you have positive camber.
8) Adjust the upper eccentric bolt to correct the angle to desired amount.
9) Recheck your camber angle using (3-7) above. Correct again if needed. Then
tighten the two bolts firmly.
10) Recheck angle again. Things can move as you tighten the eccentric!
11) Do the other wheel.
12) Jack up each wheel and take it off.
13) Tighten the two strut bolts to the correct torque.
14) Put the wheels back on and test drive.
The nominal wheel camber is about zero (maybe a little positive), but both
wheels should have the same amount within 0.5 degree of each other. Since you
know what angle you want you can make up the right thickness shims before you
start and have someone hold the square and the shim while you adjust the
eccentric bolt until the bubble is centered in the level. If for some reason the
camber was originally pretty far out of whack, you may also affect your toe-in
alignment as well. I also bought a gage for this ($30), but used to measure it
with a ruler across the back of the wheels from the center of the tread to the
center of the tread (looked for a groove that ran straight around the tire).
Then I measured the same way at the front. The front should be about 0 to 1/8
inch longer (toe-out). This is adjusted with the single adjustable tie-rod on
the passenger side. FInaly you may have to remove the steering wheel and turn it
a few degrees so that it is lined up level when driving straight.
THE ABOVE METHODS ARE NOT DEAD ACCURATE FOR ALIGNMENT AND WILL NOT CURE A CAR
WITH BENT CHASSIS OR MISALIGNED REAR AXLE, BUT IT IS USUALLY SUFFICIENT FOR GOOD
TRACKING AND TIRE WEAR.
From: Tom Leone Org: Ford Motor Company Research Laboratory Subj: Do It
Yourself Alignment
Thanks for a great article! I've done this myself only a couple of times, but
I have a few suggestions:
1) It is easy to do toe-in without finding the true centerline of your car.
Simply check the service manual for the "track" dimension for front and rear
(track is how far apart the outside edges of the tires are, basically). Set up
your string by measuring between the front and rear wheel hubs. If the front
track is wider, then the front wheel hub should be closer to the string by half
the difference in front and rear track.
2) After you make a toe change, you should bounce the car, roll it back and
forth, and re-check the measurements. I've noticed significant changes after
doing this, probably due to tire deflection. When you make a change on one side,
the tire flexes, which puts enough force on the steering rack to change
clearances and/or flex the other tire. This might not be a problem if you do
both sides at once. I don't think that locking the steering wheel is sufficient,
because there is slop in the linkage.
I posted something about this on rec.autos awhile back. I'll append my old
article to this one. I've already modified it to include your suggestion about
checking wheel runout!
I'm only going to cover the difficult part of an alignment: measurement. I
will assume that you know the basics (which nuts and bolts to manipulate, etc.)
Also, you should make sure that the wheels are "seated", by rolling car forward
and back, and jouncing up and down. Also, of course, everything should be done
on a level surface (check with a "bubble" level). You should also check your
wheel rims for runout; if the runout is significant, mark opposite places on the
rim where the runout is the same, and measure at those places.
The key to my method is recognizing how accurate you must be. On my car, the
tolerances are a few tenths of a degree. If your wheel diameter is about 15
inches, that means you must measure a displacement of the rim of 15 inches times
the tangent of a few tenths of a degree. That's 0.052 inches (for 0.2 degrees),
or 1.33 millimeters. I use a clear plastic ruler (with millimeter markings),
which I believe gives me an accuracy within half a millimeter.
Start out with the camber. Simply hang a plumb bob (a weight on a string)
over the fender. The string should be right in front of the wheel hub. Measure
the distance between the string and the wheel rim, at both top and bottom of
rim. Subtract the two, and divide by the distance between the two measurement
points. Take the tangent, and you have the camber (in degrees or radians
depending on your calculator).
After adjusting camber (and re-seating wheels each time), you can adjust toe.
The concept is exactly the same, but this time gravity doesn't help you
straighten the string. You have to get the string parallel to the car before you
can start measuring.
First, stretch the string between two jackstands, washer fluid bottles, or
whatever puts the string at the height of the wheel rims. Then measure the
distance between the string and each wheel hub (front and rear). If the front
and rear "track" are the same, then the two distances should be the same (track
is the distance between the left and right tires on one axle, and can be found
in your service manual). If the front track is wider, then the string should be
closer to the front hub, by one half the difference in front and rear track.
Double-check that the strings are the same distance apart at front and rear.
If this sounds confusing, just think it out for yourself. Just remember that
the goal is to get the string parallel to the car. After the string is parallel
to the car, follow the same procedure as for camber (measure between string and
rim, at both front and rear of rim, divide by rim diameter, and take tangent).
Note that some manuals specify total toe (left plus right).
After checking toe, bounce the car, roll it back and forth, and double-check
the measurement. It often changes because the tire was flexed after you made the
last alignment change. Have fun, and please let me know if you have any
questions, and how well it works for you. I've only done it this way twice, but
I think it works well.
From: Randy Chase (randyc2@home.com)
Regarding David's recent post about doing your own alignments, this was
posted on Team.Net by ex-MR2 autocrosser Vince Bly (he went to the dark side and
bought a Miata) Some of it may be more Miata specific, but you get the general
idea.
Reading Brett Howell's account of his experiences with N?? (ex NTW) reminded
me of similar experiences I have had with several auto shops, including NTW. I
will spare the bandwidth and not recount mine, other than to say that they
convinced me to do my own alignment. One spec. that can be very critical to
handling is toe (both front and rear). It is also one that is prone to errors.
After trying about half a dozen techniques, I've settled on string! Although
this sounds crude, it's actually very precise and the "equipment" is cheap. I've
included a brief description of the method below.
Initially, I'll describe the method assuming that the front and rear track
are the same. (This info should be in your manual.) Park the car on level
ground, put a loop of nylon twine around all four tires at hub level. Nylon
works best because it will stretch - you want a little tension. Adjust the loop
so it is level and right at hub level across each tire. Next adjust the steering
wheel so the gap between the twine and tire section is the same on both front
tires. Assume you have some toe-in at present. If this is so, the twine will
rest on the rear section of each front tire. Measure the gap between the twine
and the front tire section on each side (if you have adjusted the steering wheel
correctly, it will be the same on each side). Add the two measured gaps and
divide the result by 0.80. This adjustment is necessary since the measurement
was made at the tire section and the spec. refers to the toe at the tread. You
now have a reasonably accurate measurement of the front toe. More importantly,
you will find that, with care, the measurement is very repeatable. Of course,
you can also use it to measure rear toe - just make sure you have the steering
wheel exactly straight ahead (measured front toe is exactly the same on both
sides). If you don't, and use this method while adjusting rear toe, you can
introduce setback (a side-to-side difference in wheelbase).
There are three significant sources of error: errors due to raised lettering
on the tire section, the measurement of the gap itself, and error in the
adjustment factor to convert from the section diameter to the tread diameter. On
R type tires, the raised letters are approximately 0.020". With care and common
sense, you should be able to compensate for this, at least within 50%. This
leaves a residual error of 0.010" per side or less. If you measure the gap with
a good steel rule and take parallax into account (look it up, if you need to),
you should be able to measure the gap to within about 0.010" to 0.015". The
worst case sum of these is 0.025" per side which can be reduced by multiple
measurements. (You need to roll the car forward or backward between measurements
to change the effect of raised lettering). I have found that, using the average
of three measurements, I can come back several days later and repeat the
previous values to within 0.010" per side! I haven't worried too much about the
conversion to tread diameter (for my 50 series tires, I use 1/0.80), since I'm
more interested in repeatable measurements than absolute accuracy.
I realize that this is not a technique for those in a hurry. What it is is a
very precise measurement made by someone you trust (you).
If you don't trust someone else and are not comfortable with you present
method, try this - it doesn't cost much.
Vince Bly //Spiffy Wabba Racing // Randy Chase