Off Panhard bar

[H. J. Zivnak]

-----Original Message-----
From: Greg Hermann <bearbvd at sni.net>
To: diy_efi at efi332.eng.ohio-state.edu <diy_efi at efi332.eng.ohio-state.edu>
Date: Friday, March 12, 1999 5:22 PM
Subject: Re: Off Panhard bar


<snip>

>Or go scrounging in a boneyard that has some old Alfas. They used an upper
>triangle, with two pivot points on the chassis, and a BALL joint attached
>just to the left side of the pumpkin, plus two lower trailing arms.
>Particularly if you replaced the chassis pivots of the triangle (rubber
>stock) with bronze on steel, also if you replaced the lower rod ends with
>real rod ends, they were as NICE a live rear axle setup as you could want.

(Lurk mode off)

It's nice to have something to say !

I disagree.

Any assymmetry of the linkage will cause the car to react differently in
right hand turns than it does in left hand turns. Secondly, because the
A-arm is above the axle, and it determines the roll center heighth, the roll
center is high. In addition, since the a-arm components must absorb all
cornering forces they are subjected to extreme stress, hence the ball
joint.

This could be improved by placing the joint in the center below the pumpkin,
providing symmetry and lowering the roll center, or better  yet , replacing
the a-arm with two angled arms and eliminating the need for a high strength
joint. Come to think of it, you could reverse the angle of the arms,
attaching at the ends of the axle housing instead of the pumpkin and near to
the longitudinal center line at the chassis. Now you have a four link which
provides lateral control and eliminates the need for a Panhard or Watts.

>Another very nice set-up was the old Rover 2000 Di Dion setup--instead of a
>lateral link, they used half shafts with no slip joint, upper and lower
>arms on each side, and a slip joint in the Di Dion tube.

Huh?

Am I missing something here? I've read this three times and it still doesn't
make sense.

It sounds like they added an upper arm to a Jaguar set up to keep the De
Dion tube from pulling the side gears out of the differential on a hard
turn. With no plunge in the half shaft, the half shaft and the upper and
lower
arms would have to be parrallel and equal legnth. This would cause the tires
to move laterally with jounce, hence the slip joint in the De Dion tube. I'm
sure that this scrubing of the tires can't be all that good to begin with,
but imagine that we want to turn, and the body rolls to the outside as it is
wont to do. Because of the equal legnth control arms the tires lose camber
angle, and cornering force. All the while the De Dion is trying to further
unload the inside tire, and prolly binding up in the process.

I don't mean this to be an attack on these two examples. I think the point
is that cars roll as well as bounce. Even a Watts linkage with the bellcrank
attached to the axle will cause the axle, or the car, to move laterally if
the car is in roll when it bounces (but it won't if you attach the bellcrank
to the chassis). It is prolly more important to worry about roll steer than
lateral movement of the axle. Try driving your car backwards at any speed
above a crawl.

Another good source of info on four links is Dave Morgan. He wrote a series
of articles for National Dragster named Pitside with (you guessed it) Dave
Morgan and at least one book titled Doorslammers IIRC. Lots of illustrations
of instant center, anti-squat, center of gravity, etc. calculations. Written
for the drag racer, but applicable to a road car also.

HTH

Joe

(lurk mode on)