charlie,
i dont see how lowering the rear roll center on its own can make the car
rotate better.
that change alone will increase the CG to RC distance and acts like
softening the rear bar. for example, when i lowered my front roll
center, i calculated how much more front bar i needed to balance that
change- so i changed from a 1.25" OD, .095" wall to a .188" wall front
bar which rebalanced the car.
in the scenario you describe, was there also a stiffer rear bar added?
how much stiffer? was the geometry changed, e.g. from trailing arms to
a panhard?
but now we are describing steady state cornering- which is tuned with
bars and springs.
its the possible initial effect of the roll axis before steady state
that i am interested in. ive gotten several different, but impassioned,
arguments from various experts. unfortunately there is no agreement on
what the dominant effect/s is/are.
james
OSP - Octane's Sole Purpose
Smokerbros@aol.com wrote:
>In a message dated 7/20/2006 5:59:57 P.M. Pacific Standard Time,
>nihal@berkeley.edu writes:
>
>I don't think that it would work this way. If the rear roll center is
>lower, this does not change the total weight transfer at that axle. It
>only changes the roll angle. The roll angle is purley a function of the
>distance between the RC and cg height (the lever arm you speak of) and the
>lateral acceleration. With the lower rear roll center the car will become
>"lazy" and be more stable at that end.
>The overloading of a tire doesn't make senes to me. The weight that went
>onto that tire had to come off of another wheel (usually inside). These
>inside wheels are what govern the oversteer and understeer characteristics
>of a car. I would suspect if the front outside was in the situation you
>describe (kind of like overdriving a FWD car) the front inside wheel has
>very little weight, and thus cannot produce the lateral accelration it
>needs to, and therefore you have understeer.
>
>
>
>Okay, say it however you want to. My experience is with strut front/solid
>axle rear cars. I know the following to be true.
>
>1) MacPherson strut suspensions have a very low roll center, usually
>between 2" above ground and somewhere below ground.
>
>2) Solid axles without a Panhard or Watts have a roll center that is right
>through the center of the axle. So, on a car with 24" tall tires, this is
>12".
>
>3) That's a steep roll axis and the car will push. Lowering the rear roll
>center to say 6" above ground causes the rear to rotate more and the car to
>push less.
>
>this has been proven time and time again in numerous autocross cars. Cloak
>it in whatever math or verbage you want to, but the end result is #3.
>
>Charlie
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