Suspension Setup
and tuning
and tuning
Caster angle is the angle of the wheel's pivot or
turning line and it's centerline when viewed from
the side. It is a critical adjustment because an
incorrectly set caster angle results in extreme
wheel instability commonly referred to as
"death-wobble."
For a visual example, imagine front wheel and
handlebars of a motorcycle or bicycle. When the
handlebars and the wheel are straight up and
down this is called neutral caster. The vertical
pivot angle is in line with the wheel centerline.
Now visualize the handlebars (pivot) out in front
of the wheels centerline, this is negative caster.
Negative caster causes the wheel to be highly
unstable creating an effect: "death wobble." All
cars are designed to avoid this condition.
The preferred caster angle is a positive caster,
where the wheel's pivot is behind the wheel
centerline. This is the most stable caster angle.
The only realistic adjustment for a suspension
design is how much positive caster is built into
the suspension. Too much positive caster,
where the wheel is angled way too far in front of
its pivot, makes steering difficult. Cars are
designed to have a modest amount of positive
caster, often just a degree or two.
Caster angle diagram--wheel viewed from the side.
Caster angle examples on a bicycle
Caster angle built into wheel spindle--driver's side
front wheel viewed from the side
front wheel viewed from the side
With each suspension design there are
adjustments between each component. Some
designs like solid axle and leaf springs have few
adjustments. Independent suspensions often
have many adjustments. The difference
between a properly and poorly setup suspension
can be like night and day.
First, lets take a look at the primary adjustments
for suspensions in general.
Camber angle is the angle of the wheel to the
body, when looked at from the front of the
vehicle.
Positive camber occurs when the top of the
wheel is farther away from the car than the
bottom of the wheel. Imagine the letter 'V' or
'W' as a visual example.
Negative camber occurs when the top of the
wheel is closer to the car than bottom of the
wheel. Here imagine the letter 'A' for a visual
example.
Camber angle can affect handling characteristics.
The goal for setting camber is to maximize the
contact patch of the tire when both cornering
and driving straight. When cornering the tires
bend and deflect and the contact patch shrinks.
This minimizes traction and limits cornering
ability.
Camber adjustments can be made to keep
maximum contact patch on the ground. For
example when turning left the left (inside)
wheels gain negative camber due to the
cornering force deflecting the bottom of the tire
and centrifugal force pushing the top outwards.
Similarly, the right side (outside) wheels gain
positive camber. When the car makes a right
hand turn, the opposite happens.
A mild negative camber setting when the car is
at rest, will offset the tendency for positive
camber in a turn, on the outside wheel of a
turning car. The resultant neutral camber on the
outside wheel will maximize the contact patch
increasing traction. Weight transfer or
centrifugal force, makes the outside wheel do
most of work in a turn. Thus, maximum contact
patch, resulting from neutral camber on the
outside wheel will improve the cars ability to
make sharp fast turns.
The downside of a preset negative camber is
increased uneven tire wear. This downside is
acceptable to a race car driver who changes tires
each race, but not to a street car driver who
needs those tires to last for several years.
Therefore, camber adjustments are limited on
street cars.
Camber angle example as viewed from the rear
Left turn camber change as viewed from behind
