The problem I have is with the RC height curve shown here (with context):
Quote:
Originally Posted by RBbugBITme
This one is particularly nasty. This is a plot of -3 to 3 deg of roll at a ride height of -3 on the far left to +2 on the far right in 0.10" steps. The vertical black line is at -1" ride height which is right around where the roll center goes crazy shooting off to infinity and switching back and forth above and below the ground plane. I wouldn't personally ever set a BRZ to a 1" drop after looking at this without roll center correction.
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The roll center height plot is saying that:
1. At -1.05" ride height, roll center starts at zero (ground level) at zero roll, and rapidly goes CRAZY HIGH (way above ground) with any roll in either direction.
2. At -0.95" ride height, roll center starts at zero (ground level) at zero roll and rapidly goes CRAZY NEGATIVE (way below ground) with any roll in either direction.
Even with perfectly rigid spherical bearings all around, no way that's what happens. Such a car would exhibit zero roll in cornering at -1.05" ride height, but would immediately flop all the way to the bump stops in corners at -0.95" ride height.
I still strongly believe the math model is breaking down with roll applied when static RC height is at ground level and giving unrealistic RC height change with roll.
The roll center height calculation is based on an intersection point of a line that is tending out towards infinity. In that region, you get to a point where you can't calculate RC height with enough precision to give reasonable results.
You can run the numbers and get results, but when basing RC height which is on the order of inches on a line that's going out billions of miles and beyond, the calculated RC height value becomes kinda meaningless...
I would bet that a physics-based vehicle simulation model would give different results, and I'm *certain* that an actual FR-S/BRZ won't behave like it had infinite roll stiffness at -1.05" ride height and zero roll stiffness at -0.95" ride height even with spherical bearings all around.