Great description Count and nice observation. However, I don’t think it is applicable to the issue. If I could only draw with Paint as well as McRat, well a picture is worth . . .
So let’s try an example. If you are an overhead crane operator you will instantly understand. Picture a 3 ton weight hanging from a crane. As you start to move the overhead crane, the mass will lag behind the overhead carriage but eventually start to move forward. When the crane stops the mass will continue on for a bit. This starts a swinging action like a pendulum. To stop the swinging the crane operator watches the swinging mass and as it reaches its maximum swing point and starts back he moves the overhead carriage in the same direction. This dampens the swing and the load will hang vertical. (for illustration only. Swinging a load is dangerous and could lead to termination). Don’t ask me to explain the physics – I can’t.
We are talking about a car being disturbed for any reason and starting to move the CG from its intended path. The only forces to stop that movement are, wind,
CG mass (one of Newton's laws
), and tire-to-surface friction. (Would that be called the scrub angle?). Since we are already misaligned with the course we can assume all three forces are
not sufficient to arrest the problem.
I will use the assumptions already posted in this thread.
One rear tire is dominant. I don’t care if it is pointed left or right (toe in or out) but because it is dominant it
will drive the rear-end the direction it is pointed. One degree at Bonneville means you are pointing either left or right of Floating Mountain. Just kidding . . . don’t know exactly.
When a (zero toe) rear-end starts its deviation the CG also moves in that direction. (Think of the 3 ton mass above) The driver steers into the direction of rear-travel and by moving the front of the car in that direction it dampens out the “swing” of the CG. This allows the tire’s scrub angle to return to normal and
assist in recovery through the tire-to-surface interface (friction).
Two forces are in your favor.
Now picture either left or right toe. As the rear swings in the direction of the toe (remember it is dominant) the driver will turn the front end in that direction. The toe has already assisted to start the “swing” of the CG and is actually driving the CG
away from the center-line. As the driver turns toward the direction of the toe he actually
increases the steering angle (the left toe) away from the center line further accelerating the CG away from centerline. The “dampened-pendulum-effect” is all that you have for help because you have
worsened the scrub angle at the tire surface. The more you steer into the spin the more you drive the CG away from the cenetr-line. Very bad IMHO.
Sorry for the dissertation. McRat’s skill could have saved 1,000 words.
