roll stiffness distribution & oversteering
roll stiffness distribution & oversteering
(OP)
How can a high rear roll stiffness cause oversteering?
What I know:
1- I can increase understeering by changing the anti-roll bars with a stiffer one in front and a softer one in rear.
2- Higher roll stiffness of an axle leads to higher portion of that axle in lateral load transfer on the cornering.
3- (It might not be related but,) Stiffer springs give lower road holding.
4- Cornering stiffness is affected by the vertical load (I’m not sure but I think reversely).
What I want to know:
If (1) is true, why does it happen? why?
If (2) is true, is this a reason of 1? why?
Does a rigid suspension (not rigid axle) for rear make a highly oversteered vehicle? why?
If (4) is true, Am I right: “I can get a higher cornering stiffness (of axle) on the axle with more equal weight distribution (on its left and right)”
Thank you either you correct my probable mistakes or answer my why questions.
What I know:
1- I can increase understeering by changing the anti-roll bars with a stiffer one in front and a softer one in rear.
2- Higher roll stiffness of an axle leads to higher portion of that axle in lateral load transfer on the cornering.
3- (It might not be related but,) Stiffer springs give lower road holding.
4- Cornering stiffness is affected by the vertical load (I’m not sure but I think reversely).
What I want to know:
If (1) is true, why does it happen? why?
If (2) is true, is this a reason of 1? why?
Does a rigid suspension (not rigid axle) for rear make a highly oversteered vehicle? why?
If (4) is true, Am I right: “I can get a higher cornering stiffness (of axle) on the axle with more equal weight distribution (on its left and right)”
Thank you either you correct my probable mistakes or answer my why questions.





RE: roll stiffness distribution & oversteering
Cheers
Greg Locock
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RE: roll stiffness distribution & oversteering
Not sure what is meant by the last part of your last statement. Are you asking if the left and right wheel vertical loads are equal on the same axle having the same tires on it, will you get the highest net cornering stiffness? If the tires are at the same pressure and they are 'conventional' tires, and their plysteer and plyrat values are small, then the answer is YES. Load is the attenuator of cornering stiffness. That's stiffness as in: derivative, not coefficient: as in load normalized force. They are not the same animal. Convenient to spar with but not accurate enough to debate with the Geek Squad.
RE: roll stiffness distribution & oversteering
RE: roll stiffness distribution & oversteering
"Tires are not "springs" when acting in cornering behaviors. They are really velocity based (hence more like dampers)."
Could you please expand that statement a little, just to see if I have understand it right.
Regards
Goran Malmberg
RE: roll stiffness distribution & oversteering
If you can be comfortable with this explanation, you will be ready to fly an airplane. Last I heard, a plane with no relative air speed is not flying. Wings are dampers, too. If they were springs, you would always not be the first to arrive at the crash site.
This is the basic math model for all vehicle dynamics modeling that we do.