56 What does toe-in, caster and camber mean and how do they affect the car's handling?
Description
This article is from the VW Performance FAQ, by with numerous contributions by Jan Vandenbrande others.
56 What does toe-in, caster and camber mean and how do they affect the car's handling?
A:This is borrowed from the "alignment" archive:
CAMBER:
The camber angle is the angle a tire makes with respect
to a vertical line.
Positive Camber = Tops of tires point outward. If you
look at the front of the car you'd see:
V
FRONTAL VIEW __ ( ) W ( ) __
Tire \ \ ---------- / / Tire
-- --
Too much positive camber ==> Tires wear on the OUTside
(away from the car) more than the inside.
Negative Camber = Tops of tires point inward.
Too much negative camber ==> Tires wear on the INside
more than the outside.
Camber affects directional stability and tire wear. A
difference between the front wheel camber settings will
cause your car to pull to one side. I also believe it
will cause torque steering to become more noticable. It
is therefore very important to keep camber for BOTH tires
as close as possible.
Your car will also perform differently with different
camber settings. For street use, follow manufacturer's
setting, for race use, use more negative camber
(basically so that the inboard tire will be flat on the
road in sharp curves). Naturally, more negative camber
will wear the insides of the tires quicker.
Note however that the terminology used is often very
confusing, here is a sample (for either a GTI or Scirocco
I think):
>--<
[Jan]
> Camber = -.17 to 0.83 Degrees; which seems to imply
that they want > positive camber (tops pointing AWAY).
That doesn't sound right.
> To make matter worse, in Greg Raven's book, when he
talks about
> 2.5 Degree Camber he means NEGATIVE camber = / \. Can
someone please help
> me out with this one?
[Mark]
Right. Negative camber helps cornering power and turn-
in. The reason that they recommend positive camber is to
ensure understeer for the "average" driver. At the end
of last season, I had settled on about 2.2 degrees
negative camber while I was autocrossing.
>--<
The rear camber is not normally adjustable on most FWD
VWs.
TOE:
Toe = distance between the front of the tires and their
rears.
Sometimes express by an angle instead.
(Negative Toe) = Toe OUT = distance between the front of
the tires > rears If you were to look from the TOP:
Front
================== Bumper
TOP VIEW __ __
Tire \ \ / / Tire
-- --
(Positive Toe) = Toe IN = distance between the front of
the tires < rears
Unlike the camber settings, the individual toe of each
front wheel is not as critical (because of the steering
mechanism), but the TOTAL toe is (Toe = distance rear -
distance front of tire). Usually only one side is
adjustable, which then results in the "crooked" steering
wheel problem.
For the rear wheels the individual toes are however
important. If that's off, your car will be driving "side
ways". But you do not have to worry about it because the
rear toe is not adjustable on most watercooled FWD VWs
(w/o special equipment).
Too much toe in or toe out will also wear your tires
prematurely. The wear pattern is called "feathering" and
it will show up as a slanted wear or zig-zag accross the
tread of your tires. If you were to take a cross section,
you'd see something like (a bit exagerated due to the
limitations of this format):
_ _ _ _ _
TIRE CROSS SECTION / |_/ |_/ |_/ |_/ |
| |
Also here things get a bit confusing:
>--<
[Jan]
> The specs for Toe are even more confusing: -15'+10' = -
.25 + .17 Degrees.
> I assume the "+" is used instead of a "+/-" which
results in:
> -.25 to -.08 degrees, a slight toe in, which is more
what I'd
> expect. (Greg Raven however recommends 1/8 inch [yes,
inch] of toe OUT).
[Mark]
Right. So negative is toe-in. The only car on the
market today that comes from the factory with toe-out is
the Acura NSX. Toe-out also helps turn-in, but does
increase tire wear and gives the car a little bump steer.
It may also wander a bit on the highway. I was running
1/8" (yes, inch) of toe-out during the autocross season,
but now I'm running zero toe.
The reason that toe is often given in inches is because
it's much easier to measure that way.
>--<
CASTER:
Caster = The angle your wheels pivot about wrt to the
vertical when you steer (= the angle of front
struts/shocks wrt to the vertical?).
__
/ \ SHOCK TOWER
SIDE VIEW //|
// | angle
STRUT //
O Wheel axle
Affects of caster: It keeps the wheels running in a
straight line and causes them to straighten when coming
out of a turn. Increasing caster also provides better
handling w/o the tire wear.
Too much caster causes hard steering, too little causes
your car to wander. Caster settings do not affect tire
wear.
If you look at a car from the side, caster is the angle
the front strut makes with a vertical line, similar to
the fork on a bicycle. When you turn, the axis of
rotation of the wheels is not perpendicular to the road,
but rather at an angle:
V
FRONTAL VIEW __ ( ) W ( ) __
TURNING LEFT Tire / / ---------- / / Tire
-- --
The result is that the tires "brace" themselves against
the cars sideways movement ==> better cornering! I
believe this is one of the reasons why a Corrado SLC
(with > 3 degrees of caster) feels more stable in a
straight line, and corners better than a G60 (with ~1
degree of caster) if you ignore the softer springs and
shocks of the SLC.
Caster angles are not easily adjustable on most A1-A3
VWs. So if some shop tells you they did, question their
abilities... Note: Still under investigation! By changing
the subframe to that used on an SLC, a greater caster
angle can be achieved. More drastic changes involves
moving the shock towers.
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