Found a typo:
In general, on the front suspension, lowering the roll center decreases...
Should be:
In general, on the front suspension, _raising_ the roll center decreases....
Rick Brown
BP Corvette
-----Original Message-----
From: owner-autox@autox.team.net [mailto:owner-autox@autox.team.net]On
Behalf Of Rick Brown
Sent: Monday, April 01, 2002 10:47 AM
To: Jay Mitchell; autox@autox.team.net
Subject: Interesting suspension question
Other effects are that jacking forces increase but shouldn't be an issue at
the front of a front engine, rear drive car.
Also, weight transfer dynamics are altered since weight transfer will occur
more quickly on the your front end now since raising the roll center
increases the relative amount of weight transfer through the roll center to
the unsprung mass and decreases the amount of weight transfer due to couple
around the roll center. The former transfers very quickly and the latter
more slowly since it is resisted by roll inertia and suspension springs,
damping and anti-roll bars.
In general, on the front suspension, raising the roll center decreases
roll, increases jacking, increases ride height, and improves turn in. A
roll center below the ground increases roll, creates anti-jacking, lowers
ride height and reduces turn in response.
Rick Brown
BP Corvette
-----Original Message-----
From: owner-autox@autox.team.net [mailto:owner-autox@autox.team.net]On
Behalf Of Jay Mitchell
Sent: Monday, April 01, 2002 5:04 AM
To: GSMnow@aol.com; autox@autox.team.net
Subject: Re: Interesting suspension question
GSMnow@aol.com wrote:
>What effect will raising the front roll center have?
You have it pretty well figured out. If you raise the RC height
and leave the CG height alone, you'll reduce the roll compliance.
The effect is the same as stiffening the swaybar or springs at
that end.
>This should increase the
>weight transfer taken by the front wheels, whikle reducing the
weight
>transfer taken by the rear wheels.
That's correct. The effect of raising the roll center is that a
larger percentage of the vertical load applied to the outside
wheel is passed directly through suspension links rather than
through the spring. Ergo, more load transfer to the outside wheel
for a given amount of body roll.
>So this (I assume) will decrease oversteer
>(or increase understeer) just like more front sway bar.
Yes.
>This is on a rear
>drive car, and I was lifting the inside rear tire off of the
ground killing
>traction at corner exit.
You definitely don't want to do that. Even if it takes creating a
substantial push to fix it, you'll go faster if you can
accelerate out of turns.
>The transition between the
>understeer and oversteer made it so when I had it dialed in for
good neutral
>balance with all the tires on the ground, I had to drive a bit
under the
>limit to run clean.
In a RWD car with same-size wheels and tires at all four corners
and any amount of power, you may have to accept a little bit of
push to keep both drive wheels firmly planted during corner
exits.
>My hope is that the tire will stay on the ground, and I can
adjust camber,
>toe, and if needed, spring rates to balance the undrsteer back
out.
If you reduce roll couple by raising the front roll center then
reduce front spring rates to get rid of the resulting understeer,
you'll be back exactly where you started. If you're losing front
grip because of alignment parameters, you can improve matters by
dialing in camber/caster.
>Front weight bias is only 52%.
Based on that, I'd guess that you should be able to get the car
pretty close to neutral while keeping the inside rear wheel on
the ground.
Jay
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