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The best way to make sure you're both safe and fast
is to have the right chassis set up
believe me, there is nothing worse
than fighting an ill handling car
the suspension of a modern race car
has one simple purpose
control the tires
making sure the contact patch of each
is in maximum contact with the track
at all times
in this section, Jay O'Connell
Technical Director for Rahal, Letterman, Lanigan Racing
will explain the basics
starting with camber
camber is the angle of the tire
relative to the vertical
if it's straight up
perpindicular to the road, then it has zero camber
If it's tilted towards the center line of the car
that would be negative camber
if it's tilted away from the center line of the car
that's positive camber
It turns out that tires give you the most
grip when they have a little bit of negative camber
so the key is keeping it
on the negative side around the whole lap
not too negative, but certainly not positive
While the camber angle is set statically
with the car on a perfectly flat surface
it's designed to operate on a
race track that is anything but
perfectly flat
You want to think about, what is the camber
going to be in the middle of a turn
you'd like that to be on the negative side
depending on the tire, maybe one, two
three degrees negative
For example, on an indy car, since we're always
going to the left, we'll have positive camber
on the left front tire
negative camber on the right front tire
so they're both pointed in the turn
when you're actually at 4 Gs in the middle of a turn
and both of them are right about 1/2 degree negative
right at the optimum for grip
how do you tell when the camber angles
are right? and what adjustments
can you make to hit that sweet spot
You adjust the camber by looking at the
tire temperature profile as it comes in off
the racetrack, so if the tire
temperature is saying the insides are a lot hotter
than the outside, then you probably have a little
too much camber, too much negative camber
and if the tire temperatures are hotter
on the outside shoulder than the inside then
you need to put more negative camber in, tilt the
tire in more to even out
those temperature profiles on the tire
another key adjustment is
caster angle, which affects how
stable the car feels as well
as how heavy the steering feels
caster angle is a measurement in
the front suspension that
determines how much self-centering
the steering and the
suspension system will have when you're in a turn
caster, like on a bicycle
the same terms used on a bicycle
how much angle there is on
the head of the bicycle around the steering
axis that goes into the ground
another way to think about it
is like a shopping cart
shopping carts, when you push them down
the wheels all center up, and
that's because the wheels have a
caster to them, or caster angle to them
basically,
the center of the tire, where
it touches the ground, as long as that's behind
the steering axis
then it self centers and goes straight
if you put more caster in you get more
self centering, you get more
more steering effort
off center at speed
You might think a car should be set up
perfectly square, with all four wheels pointed
straight ahead, but in reality
small adjustments in the toe
in or out can make quite a difference in how
well the car turns into a corner
The toe is looking from the top view
is the angle between
between the tires
if the tires are toed-in
just like you're feet being toed in
being pigeon-toed
if you toe the wheels out
the front of the tires are
further apart than the back of the tires, you're toed-out
the tires are
much more sensitive to toe than
they are to camber, so it's important to get
the toe close to zero
in the front and the rear
to minimize the drag from the tires
So what is the ideal set up?
Normally you would
set the front toe a little bit
of toe out, and that
makes the car roll nice
and freely, and it enters the corners a little
more easily, because if you toe in
the front then you have to fight the steering across
center before you turn in
and then on the rear you would set
a little bit of toe-in, because that's
you need that in the back for stability
especially when you're putting power down
if you put toe out in the back the car spins
quite easily and can be quite tricky
to drive
And then there's the little pesky issue of
of bump-steer, where the toe changes
as the suspension moves up and down
Bump-steer is a
great topic because it relates back
to the toe we just talked about
bump-steer means that the wheels
steer as they go up and down
or hit a bump, ideally
we don't want any bump-steer
of such that when you hit a bump, the wheel
just tracks up and down and doesn't affect steering
steering wheel at all, especially
at the rear, if there is any bump-steer at the rear
the car will start to manuever
over bumps as if it's a
hook and ladder truck when the guy in the back is
doing his own thing, that's the worst case
for a driver if the back of the car is
unpredictable and moving around on its own
that gives the driver a very bad
bad feeling about what's happening
bump-steer is very critical at the back
and fairly critical at the front
and if anything, we try to set up
bump steer so if anything it's a little towards the
stability direction, which means a little bit of understeer
on a bump, as opposed to oversteer
Now we get to some trickier stuff.
Ackerman, which is
the ability of the steering to compensate
for the fact that the inside
front tire actually carves
a tighter radius through a turn
than the outside front tire.
Ackerman is another aspect of steering
that determines how the toe is changing
from the straight ahead position to the
middle of the turn position
if you have a lot of ackerman, the inside tire turns
a lot faster than the outside tire
so that both tires stay on
what would be the optimum line for the least
amount of scrub, and this is how most
street cars are set up so when you're manuevering
in and out of parking spaces in the parking lots
you don't burn the tires off the car
whereas in a race car
you might want to have some ackerman
or some anti-ackerman, where the
inside wheel turns less than the outside wheel
if you're trying to get more grip out of
a particular set of tires
We do use ackerman depending on the course
to get a little more grip out of the front tires
SAFEisFAST.com