>I am really trying to understand the basic of Nascar 4 car 'set up' in order
Hi Paul,
One way to think of it is like this: When a car is in a "steady state" turn,
meaning the car is following a constant curve without speeding up or slowing
down, and you've got the steering wheel in one position, the car wants to roll
to one side. If it's turning left, it rolls to the right (you know this
already). The springs on the right side are being compressed, which does two
things: It pushes the wheels down harder into the ground, and it pushes up on
the right side of the car, preventing it from rolling any further. The
opposite is happening on the left side. The springs are extending, so they
aren't pushing down on the left wheels as hard as they were before, and they
aren't pushing the left side of the car upwards (rolling it) as much.
Eventually, the car sets itself at a constant roll angle.
If the car rolled 2 degrees while turning through the corner, the springs on
the right side might compress 1 inch. (They probably compress more than this,
but just for example) A spring rate of 300 lbs per inch means that if a spring
is compressed one inch, there will be 300 lbs of force pushing up on one corner
of the car, and also pushing down 300 lbs on the tire. Make sense? If we
doubled the spring rate on the right front tire to 300 lbs and assumed the body
still rolled about 2 degrees in the corner as before, still giving 1 inch of
spring compression, there will now be 600 lbs of force pushing down on the
tire, instead of 300 like before. There's now more "weight transfer" at that
wheel.
In reality, increasing the spring rate will cause the body to roll a little
less than 2 degrees now, so you wouldn't quite get the full 600 lbs of force
pushing down instead of 300, but you'd still wind up with more than 300 lbs of
force.
Anyway, the total force at all four tires is going to equal the weight of the
car (if we ignore the aerodynamic downforce.) This means the force is going to
be less at another wheel because of this.
I'm not sure how much you care for the mathematics behind this stuff, but
here's a simplistic example of how you might estimate the force pushing down on
each wheel (wheel load) if you know how much the body is rolled in a corner.
Studying this may help you understand better what is happening when you change
spring settings in Nascar 4.
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We could have four springs, RF (right front), RR (right rear), LR (left
rear), and LF(left front). The spring rates might be:
RF = 300 lbs/inch
RR = 300 lbs/inch
LR = 300 lbs/inch
LF = 300 lbs/inch
If our car rolls 3 degrees to the right in the corner, which might cause 2
inches of spring compression/extension, we could estimate out how much weight
transfer there is at each wheel. For note, the * sign means times, or
multiplication.
Weight transfer at right front (RF): 2 inches * 300 lbs = 600 lbs
Weight transfer at right rear (RR): 2 inches * 300 lbs = 600 lbs
Since the car is rolling to the right, the springs on the left side are being
extended rather than compressed, so they're not pushing as hard as they were
before. We can show this by multiplying by -2 inches instead of +2 inches.
Weight transfer at left front (LF): -2 inches * 300 lbs = -600 lbs
Weight transfer at left rear (LR): -2 inches * 300 lbs = -600 lbs
As we can see, all four wheels here have changed they're "load" by 600 lbs.
The left side by -600 and the right side by +600. From a birds eye view of the
car, it might look like this:
-600 600
-600 600
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If we wanted to stiffen up the right and left front, we could do it again:
The spring rates might be:
RF = 400 lbs/inch *< This is a stiffer right front spring
RR = 300 lbs/inch
LR = 300 lbs/inch
LF = 400 lbs/inch *< This is a stiffer left front spring
If our car still rolls 3 degrees to the right in the corner, causing 2 inches
of spring compression/extension as before, we could estimate out how much
weight transfer there is at each wheel with the stiffer front end.
Weight transfer at right front (RF): 2 inches * 400 lbs = 800 lbs <--stiffer
spring
Weight transfer at right rear (RR): 2 inches * 300 lbs = 600 lbs
Since the car is rolling to the right, the springs on the left side are being
extended rather than compressed, so they're not pushing as hard as they were
before. We can show this by multiplying by -2 inches instead of +2 inches as
before
Weight transfer at left front (LF): -2 inches * 400 lbs = -800 lbs <--stiffer
spring
Weight transfer at left rear (LR): -2 inches * 300 lbs = -600 lbs
So now the weight transfer situation looks like this (birds eye view of car):
-800 800
-600 600
Notice here that there is more weight transfer at the front than at the rear.
In reality, if you totaled the numbers from the first set of four (with equal
spring rates) and this set of four, they should end up at the same number.
They don't here, because in the real car the roll angle would be smaller with
the stiffer front end. But still, you can see that there will now be more
weight transfer at the front of the car than at the rear.
What does this mean? Because of a factor called "load sensitivity" in tires,
the total force at the front end of the car will now be less than what's
available at the rear, so the car will tend to go more straight (understeer)
with the stiffer front end. If you'd like to see a little more math explaining
why this happens, let me know.
Off the top of my head, I'm not sure what would happen if you stiffened up
the front right and softened the left front.
Whoops, you're posting from UK, I should have used metric!! Sorry!
Todd Wasson
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