The primary role of a panhard rod is transverse axle location. With
standard suspension there is little to stop the entire wheel/banjo assembly
from moving laterally under cornering load. There is enough bending and
twisting of the springs (and for 1/2 elliptic the rear spring hangers) that
the whole assembly can easily move > 1/2". the panhard rod prevents
this lateral motion.
The secondary role is to optionally modify the roll center of the rear
suspension.
This is a very brief discussion of what it means. For a better, more
accurate,
and more complete review see a book like Puhn's, Carroll Smith's, Van
Valkenburg, or haney and Braun.
The roll center of a spridget rear suspension (all solid axle suspensions)
is the center of the "axle line". i.e. some 8-12 inches off the ground
depending on tyres. This is not ideal for high performance suspension. With
a panhard rod, the roll center becomes the height of the panhard rod at the
point it crosses the centerline of the car. This could be 0-5" below the
standard
roll center. The 5" max is a guess. Mine is about 3-4" below the axle line
I think.
By changing the roll center at the back you change the roll axis of the car
and this in turn affects the cars tendency to understeer/oversteer.
The roll of a sway bar is completely different. It's purpose is to reduce
the
amount of body roll. It does this by transferring load from one side of the
car to the other. In doing so, it actually decreases the overall level of
grip
at that end of the car (all other things being equal). If you use a rear
sway
bar on a Spridget (without a LSD or locker) you'll just create lots of
inside
wheelspin and little real benefits.
Interestingly, Spridgets see an increase in front-end grip by using a
reasonably heavy sway bar. This is because all other things are *not*
equal - the suspension geometry on a Spridget has very poor camber
control which results in dramatically reduced grip with body roll,
especially
with nice fat modern radials. A sway bar at the front increases grip in this
case because the greater loss of grip is via the horrible positive camber it
prevents. As an aside this is another reason why static negative camber
is so popular and effective on Spridgets.
Note that most radials provide maximum cornering grip with some
negative camber.
If I rattle on any longer this will turn into an essay. Ask more specific
questions
if you like or go and borrow any of those books!
Mike
----- Original Message -----
From: <Ajhsys@aol.com>
To: <spridgets@autox.team.net>
Sent: Friday, 9 July 1999 2:21
Subject: Re: Panhard rod question
> In a message dated 7/7/99 6:18:15 PM Eastern Daylight Time,
> Mymgmidget@AOL.COM writes:
>
> << What are the advantages of
> the panhard rod anyway other than eliminating axle hop. Do they keep the
> axle square on hard cornering also ?? >>
>
> - - - - - - - - - - - - - - - - - - - - - - -
>
> I'll let my ignorance show a bit here, but that's how we all learn. I'd
like
> to hear (read) an explanation of panhard rods also. What is the
difference
> between that and an anti-sway bar, and how does each work? Where is each
> connected to the car.
>
> Some autocrossing is in the future of my Midget, if I ever get it on the
road.
>
> Thanks,
>
> Allen Hefner
> '77 Midget
> '92 Mitsubishi Expo LRV Sport
>
|