Quote:
Originally Posted by serialk11r
If I understand correctly, springs can only resist so much transfer. When under lateral acceleration, you have weight transfer due to the "torque" acting on the car around the center of mass (which creates body roll) and then you have weight transfer due to body roll itself, which actually moves the center of mass outward. Stiffer springs resist the movement of the center of mass outward, but I imagine the more important role they play is to resist unfavorable camber changes which kill grip more...not sure on this though.
With a lower center of gravity, you experience less "torque" on the body because the angle at which the force acts is smaller. Since the center of mass is closer to the ground at any given angle of body roll it's moving a smaller distance horizontally as well, and you should be able to use softer springs because they don't need to counter as great of a force for the same weight.
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I think of it in terms of leverage, which may be incorrect from a physics point of view, but whatever... The length of the 'lever' is from the roll center (intersection of points based on tire contact patch and angles of certain control arms. Or something... Can be above or below ground.) to the COG. So lower COG = less leverage to roll the car side to side, or pitch it front to back. Other way to resist roll/pitch is through wider track/longer wheelbase. Then we have anti-roll bars that are torsion bar springs that resist roll but not in pitch. Lastly (well, may be more, Old Greg is the guy to ask, I think) we have 'anti' suspension geometries that angle the motion of the control arms to act as a 'ramp' and naturally there are centers and the COG plays a role as well with them. COG can affect the % of anti-dive (forward pitch under braking) or anti-squat (rearward pitch under acceleration).
As for the camber change, that depends on the geometry. With the struts in the front, this
can lose negative camber as it travels, so resisting roll can help. But with the double-wishbone (really mutli-link with an upper wishbone) rears depending on the lengths of the upper and lower arcs the car
can gain negative camber as it travels.
I'm sure complicated tuning is required to optimize the roll rate to available grip and there may be tradeoffs between loading a tire (which increase its grip, up to a point) and optimizing its contact patch. As well as balancing load and contact patch side to side, front to rear, in steady state and transient movements, changing mass (passengers, decreasing fuel load). deflections of bushings, control arms (Old Greg's educating me about E there...), tires, chassis etc... Ouch... Partly why suspension has the 'black art' bit associated with its tuning.
Though I get the impression, Serial, that once you've looked at a few diagrams and done some calculations you'll have a
vastly better understanding than myself. Stupid physics...
Are you still considering Formula SAE?