John, Theo, and Mike, this is a very good thread and helps me understand
the dynamics of the rear suspension. I feel like I am now at
Suspension-102, although your comments are Suspension-505.
Are either of you, or others on the lists, using some form of rear
suspension that you like and feel would make the car more neutral? I am
using the stock MKI setup, with the panhard rod.
On a different issue, when I installed the new sway bar from Rick, by
myself, I added silicone grease to the bushings because I could not get
them on the bar. After installing, the right side does not fit fully in
the bushing, and the left side of the bar sticks out by the same amount.
I had a friend, Thanks Harry, get under the car with me after I had
installed the bar, and push-pull the bar into position, but after we let
the car down from the jacks, it went back into the same position, which
is about 1/4"-3/8" off on the width of the bushing which I am guessing
is 1 1/4" wide.
Is this a problem, and if so, should I take it out, clean the silicone
off and reinstall with soapy water, which I probably should have done
the first time. These bars are fun to put on by yourself. I know I
looked real funny with my foot holding the other side, as I connected
the first side, all the time trying not to scratch the new paint.
Thanks
Larry
"Smit, Theo" wrote:
>
> Okay, John's analysis makes some sense, and it's the first explanation I've
> heard for why having the Panhard bar one way vs. the other should make a
> difference.
>
> To answer Mike's question, a properly configured torque arm should only
> resist axle torque, and a properly set up Panhard rod should only resist
> lateral deflection of the axle. These two should be able to be used together
> to get rid of a whole lot of undesirable behavior. The wild card is how you
> think the leaf springs get into the picture, and cause binding or other
> secondary effects (as an example, running hard urethane front spring
> bushings will make the leaf springs act as anti-sway bars because on any
> turn you're twisting them as well as compressing and extending them).
>
> My opinion is that for lateral location, a properly set up Panhard rod
> (locate it horizontally, as low as you can without hitting the rear cover,
> the tire well, or running into the exhaust system) is the way to go because
> it's simple and it will work. If you are a stickler for proper rear axle
> motion, then build a Mumford link and you'll be able to set the roll center
> below the pavement if that's what you want. A Watt's linkage is a waste of
> time because there are three moving/rotating parts, two frame brackets, and
> a big rear axle bracket required, and even with all that you end up with a
> roll center that's higher than what you can get with a Panhard rod.
> Actually, to have things more correct (move the roll center with the chassis
> rather than the axle) you should put the center pivot on the frame, and to
> do that you have to build a big structure onto where the tire well used to
> be.
>
> Regards,
> Theo
>
> -----Original Message-----
> From: Carmods@aol.com [mailto:Carmods@aol.com]
> Sent: Wednesday, December 20, 2000 8:40 AM
> To: owner-tigers@autox.team.net; tigers@autox.team.net
> Subject: Re: RE; Panhard Rod
>
> To those interested in Panhard locations, here is my analysis to answer some
>
> of the recent questions.
>
> The stock Mark I rod runs from below the wheel centerline of the axle on the
>
> left side to high on the body on the right side. The Mark II runs the
> opposite direction. The instant roll center of the rear suspension is
> defined
> as the point at which the Rod intersects the centerline of the car.
>
> When accelerating out of a RIGHT turn, the body rolls to the left, raising
> the right pivot. When this happens the instant roll center of the rear rises
>
> increasing the roll stiffness of the rear suspension. Two things now happen.
>
> The engine torque into the rear axle as well as the increased rear roll
> stiffness cause vertical loads to be shifted from the right rear and the
> left
> front tires to the left rear tire. As the left front and right rear tires
> lose vertical loads they lose cornering power. These cornering forces are
> additive and transferred to the left rear tire. As the force exceeds the
> tire
> capability there will be an extreme oversteer in right turns and lifting and
>
> spinning of the right tire.
>
> When accelerating out of a LEFT turn, the body rolls to the right, lowering
> the right pivot. When this happens the instant roll center of the rear
> suspension lowers, decreasing the roll stiffness. Again two things happen.
> The engine torque into the rear axle as well as the decreased rear roll
> stiffness causes cornering force capability to be shifted to the right front
>
> tire. As the force exceeds the right tire capability the car will have
> understeer. Having a car that handles different when turning left or right
> is
> not fun.
>
> With the Tiger Mark II, which has the Panhard Rod running from the right
> side
> of the axle to the left side of the body, the opposite dynamics happen and
> these loads subtract from each other. The left and right turn differences
> are
> improved and it is easier to balance front and rear roll stiffness.
>
> So, to improve the Tiger rear geometry in order of complexity, you can
> change
> the Panhard Rod to the Mark II design, make the Panhard Rod horizontal by
> lowering the frame attachment pivot or install a Watt's linkage. Good luck
> in
> finding room and feel free to add more ideas.
>
> John Logan
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