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Re: Interesting suspension question

To: "Rick Brown" <rbrown7@pacbell.net>, <autox@autox.team.net>
Subject: Re: Interesting suspension question
From: "Jay Mitchell" <jemitchell@compuserve.com>
Date: Mon, 1 Apr 2002 13:15:06 -0600
Rick Brown wrote:

> 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.

That's correct. You don't have to wait for the springs to
compress for the "non-rolling overturning moment" (per Milliken)
to become effective.

> In general, on the front suspension, lowering the roll center
decreases
> roll,

There must be a typo there. If the RC is at the same height as
the CG, there will be _zero_ rolling moment (but obviously not
zero load transfer). As the RC height is reduced relative to CG
height, a rolling moment is established which becomes greater as
the roll center is lowered.

Usually, lowering the RC is the result of lowering ride height,
which, of course, lowers the CG as well. With my car's front
suspension, the RC drops almost twice as much as the CG when you
lower the ride height. Rather than use ride height to tune roll
compliance, I got better results setting the ride height where I
wanted it for other reasons (lowest possible CG) and then tuning
the car's roll rates to get the cornering balance I wanted.
That's for a Street Prepared car, though. In Prepared, you have
the freedom to take additional measures to set the RC height more
or less independently of ride height.

Jay

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