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Wheel Alignment 101
There are 3 main components that need
to be taken into account to make sure all 4 tires of a car meet the road
correctly. They are called "Camber", "Caster" and "Toe In".
Camber
Camber is the angle of the wheel, measured in degrees, when viewed from
the front of the vehicle. If
the
top of the wheel is leaning out from the center of the car, then the
camber is positive ,if it's leaning in, then the camber is negative. If
the camber is out of adjustment, it will cause tire wear on one side of
the tire's tread. If the camber is too far negative, for instance, then
the tire will wear on the inside of the tread. If the camber is
different from side to side it can cause a pulling problem. The vehicle
will pull to the side with the more positive
Castor
When
you turn the steering wheel, the front wheels respond by turning on a
pivot attached to the suspension system. Caster is the angle of this
steering pivot, measured in degrees, when viewed from the side of the
vehicle. If the top of the pivot is leaning toward the rear of the car,
then the caster is positive, if it is leaning toward the front, it is
negative. If the caster is out of adjustment, it can cause problems in
straight line tracking. If the caster is different from side to side,
the vehicle will pull to the side with the less positive caster. If the
caster is equal but too negative, the steering will be light and the
vehicle will wander and be difficult to keep in a straight line. If the
caster is equal but too positive, the steering will be heavy and the
steering wheel may kick when you hit a bump. Caster has little affect on
tire wear and can not be changed on the Gallardo.
Toe-in
The
toe measurement is the difference in the distance between the front of
the tires and the back of the tires. It is measured in fractions of an
inch in the US and is usually set close to zero which means that the
wheels are parallel with each other. Toe-in means that the fronts of the
tires are closer to each other than the rears. Toe-out is just the
opposite. An incorrect toe-in will cause rapid tire wear to both tires
equally. The tire pattern will have sharp edges. If the sharp
edges of the tread sections are pointing to the center of the car, then
there is too much toe-in. If they are pointed to the outside of the car
then there is too much toe-out. Toe is always adjustable on the front
wheels and on some cars, is also adjustable for the rear wheels of some
cars like the Gallardo.
Four-Wheel
Alignments
There are two main types of 4-wheel alignments. In each
case, the technician will place an instrument on all four wheels. In the
first type the rear toe and tracking is checked, but all adjustments are
made at the front wheels. This is done on vehicles that do not have
adjustments on the rear. The second type is a full 4-wheel alignment
where the adjustments are first made to true up the rear alignment, then
the front is adjusted. A full 4-wheel alignment will cost more than the
other type because there is more work involved. For a Gallardo we
need a 4 wheel alignment.
Other facts every driver should know about wheel
alignments.
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A proper wheel alignment should always start and end
with a test drive.
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The front end and steering linkage should be checked
for wear before performing an alignment.
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The
tires should all be in good shape with even wear patterns. If
you have a tire with excessive camber wear, for instance, and you
correct the alignment problem that caused that wear, the tire will
now be making only partial contact with the road. (see illustration
on right)
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Pulling problems are not always related to wheel
alignment. Problems with tires (especially unequal air
pressure), brakes and power steering can also be responsible. It is
up to a good wheel alignment technician to determine the cause.
The Suspension System of a
Gallardo
As you might expect the suspension system of a Gallardo
is a little bit more complex. The car has a double wishbone front and
rear suspension, an anti-roll bar, and anti-dive and anti-squat 'self
adjusting' Koni FSD dampers. Unlike many "standard" cars, the camber and
toe-in is not adjusted by adjusting an bolt or two. Instead, the
lower wishbone where is attached to the frame of the car is moved
in or out by inserting metal shims between the frame and the wishbone.
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Figure 2. Gallardo Wishbone and Shims |
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Figure 3. Shims |
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Figure 4. Opening shim bolt |
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Figure 5. Removing shim. |
This very simple arrangement is quite effective and easy for a
technician to do. To adjust the camber you just add or remove both shims
(A in figure 2). This has the effect of pulling in of pushing out the
base of the wheel. The shims are held in place by two bolts (figures 4 &
5). You simply have to loosen the bolts for the shims to drop
down. To adjust the toe-in you add or remove one or more shims from the
front or back (but not both) attachment points. It's the same
process for the front or back wheels. This is in marked contrast
to the setup on say a Ferrari 360 where you need a special tool to get
to the to the shims that are on the top wishbone of the front wheels.
OK, this is all and fine, but how do you measure wheel camber, toe in
and castor. Now there are several write-ups on the web describing
how you can do a wheel alignment yourself at home using a string, spirit
level and plum line. However for something as important as this
your best bet is to go to a tire alignment shop and get is accurately
done by somebody who knows what they are doing. There are several
alignment machines that use laser beams to really accurately measure
your wheels. "Hunter " is one well known brand. A typical setup is
shown in Figures 6.
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Figure 6. Typical
Alignment Shop |
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Figure 7.
Temporary Home Made Shims |
The only complication is that most machines do not have Lamborghini cars
in their computer database. If this scares off the technician you
are probably going to the wrong guy anyway. For a Gallardo let them set
it up as a Ferrari 360. What they do need is the wheel settings.
Here is what I have from the '05 factory manual. It is probably the same
for all Gallardo's. As you can see there is no Castor adjustments.
Rear Wheels |
Front Wheels |
Camber |
-1'30'' to
-1'20'' |
Camber |
-0'40'' to 0'50'' |
Toe-in |
+0'05'' to +0'06'' |
Toe-in |
+0'01 to +0'03'' |
Now in my case for a less negative camber I had to remove shims. If you
need to have a more negative camber (for example track racing etc), you
will need to insert extra shims. Lamborghini supply these in 0.3,
0.5, 1, 1.5, 2, 2.5 and 3mm thicknesses. Of course your corner alignment
shop will not normally have these in stock. What can you do. Well
if you are not in a rush, order a batch from your Lamborghini dealer or
web sites like
LamboStuff.
If you need something in a hurry you can make temporary shims out of
different sized washers (fig 7) and use these to exactly determine the
shim thickness you need. You can order this size from Lamborghini or cut
your own from some aluminum strips. Use a micrometer to make sure you
have the right thickness.
Tires
The standard Gallardo comes with Pirelli PZero 235/35/19
on the front and 295/30/19 on the back. Unlike most cars you have
to be careful with Lamborghini cars that the outside diameter of the
rear and front tires exactly match those supplied with the car from
Lamborghini.
This is because these cars have a "Viscous Traction" (VT) front/back
differential system that mechanically springs into play if it detects
slippage in the form of a rotational difference between the front and
rear tires. Its a great system that really prevents burning rubber
with fast starts etc. but is a pain in that you really have to be
careful which tires you use. If there is a diameter mis-match the VT
system will be working all the time and will over-heat/burnout.
There is a great web tool for calculating tier dimensions at
Miata.net.
Now all of the above would not be much of an issue if it was not for the
fact that Pirelli is a very poor supplier of tires like this to the US.
Currently the Pzero 295/30/19's are back ordered at most shops
--often by months! Fortunately I found that there is one
alternative tier that has the same dimensions and characteristics as the
Pirelli 295's. They are the Michelin Pilot Sport PS2's. After much
asking around I found that a number of people are using these on their
Gallardo's and are very satisfied. They even seem to ware better
-- but for me only time will tell that. Since there is little ware
on my front tires I went with just PS2's on the back. The tread
pattern is essentially the same as Pirelli's and I have seen no handling
difficulties well over 100MPH (on the track of course!).
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