Oval Track Panhard Bar-Which side should be adjusted
David Ziegelheim
If you watch the Winston Cup, the practice seems to be to adjust the
chassis side of the Panhard Bar to adjust handling. This seems wrong to
me.
First, I believe you want the bar level to minimize roll steer effects.
Second, the Panhard Bar is the only link transferring lateral forces.
The rest of the links are longitudinal with rod ends. The height of the
link mounting to the solid rear axle determines the moment around the
contact patch (or other reference point). The lateral force is the
lateral force threw the rear tires. The chassis mount should only
effect the angle of the bar, and on a long an initially level Panhard
bar this angle is small (for contrast the left upper a arm is 8" long at
15 degrees, the Panhard rod is 33-40 inches long at 0 degrees.)
So, the outer adjustment should have virtually no effect.
Am I right?
David
Allen Madding
yes, BUT the bar is not set level initially and the raising and lowering
of the bar also moves the location of the rearend laterally giving some
change in the tracking of the rear end which can loosen or tighten the
car. Teams have been converting to a new adjustable setup that allows
raising and lowering both ends. This has just been adopted this season
as it was introduced around April, I believe from Hutcherson-Pagan, but
I don't remember for sure.
Now here is a question for everyone to chew on...
A stock Monza has a panhard bar which is mounted to the chassis on the
right side and the rearend housing on the left side (which is backwards
to the desired placement). Rules as they are, our division says "NO
altering stock suspension". This means we can't correct it by swapping
things around. So if we adjust the panhard bar backwards to the way one
would be normally adjusted, do we get the same result?
Allen #13
Wade Tschida
Unfortunately, I cannot give you the Technical Terms to back this up, but I can
give you a "Real World" Testimonial. We converted a 3-Link "Dirt" WISSOTA Super
Stock to run on Asphalt. We swapped the Panhard from being dirt-optimized i.e.
mount to right-tube/left-chassis (like your Monza-I assume) to being Asphalt
optimized i.e. left-tube/right-chassis. The function of Roll Center is what the
panhard height, regardless of angle is controlling(AFAIK) doesn't change either
way you mount it. It is "optimized" for one or the other based on whether the
panhard is in "Tension aka being stretched" or "Compression-being squished".
This is how it was explained to me anyway-hey I just drive the thing. Well...3
weeks into the season, someone who gets beat on a real regular basis, finds
wording in an obscure rule/dimension diagram that the axle tube mount is
supposed to be on the right side. So we changed it back. The other guy kept
losing. The car didn't slow down. The HEIGHT of the CENTER of the panhard still
controlled roll center the same.
Happy Lappin'
Wade Tschida
tsch...@tc.umn.edu
Robert Small
The panhard rod determines the location of the roll centre.
Where the centreline of the panhard rod crosses the car centreline
that is the roll centre.
With a right side body mount bar, when the car turns left and the body
rolls right, the body mount point drops. The left side (on the axle)
stays at the same height. This gives a _lowering_ of the roll centre.
With a left side body mount bar, when the car turns left and the body
rolls right, the body mount point rises. The right side (on the axle)
stays at the same height. This gives a _raising_ of the roll centre.
What do you want it to do?
==
Bob Small
Dan Pinkham
In article <N.011797....@gold.tc.umn.edu>,
tsch...@tc.umn.edu (Wade Tschida) wrote:
The function of Roll Center is what the
>panhard height, regardless of angle is controlling(AFAIK) doesn't change
either
>way you mount it. It is "optimized" for one or the other based on whether
the
>panhard is in "Tension aka being stretched" or "Compression-being
squished".
>This is how it was explained to me anyway-hey I just drive the thing.
Well...3
>weeks into the season, someone who gets beat on a real regular basis,
finds
>wording in an obscure rule/dimension diagram that the axle tube mount is
>supposed to be on the right side. So we changed it back. The other guy
kept
>losing. The car didn't slow down. The HEIGHT of the CENTER of the panhard
still
>controlled roll center the same.
>
>Happy Lappin'
>Wade Tschida
True, but as the car corners, the roll center changes, and the change is
more or less beneficial relative to which side the bar is mounted.
**********************************************
All answers are replies,
but not all replies are answers.
**********************************************
David Ziegelheim
Bob,
The problem is the rear axle doesn't know anything about roll center's.
It only knows about the forces applied by the Panhard rod at the point
of attachment to the axle.
The change of the mounting on the chassis side does not change this
point of attachment, only the angle at which the forces are applied.
Assuming 1500 lbf lateral force through the axle, a 1 inch chassis
height change on a 35 inch bar would amount to 25 lbf vertical force at
the bars attachment point to the axle. This would probably amount to
about 25 ft-lbf of torque around the inner tire's contact patch. Not
much for 11 turns of the screw! There would be no change to the lateral
force (1500 lbf) or the torques resulting from it.
By contrast, lowering the axle attachment point one inch (without
changing the chassis mount) would create 25 lbf downward force, but
reduce the torque around the inside wheel contact point by 125 ft-lbf!!!
David
Robert Small
David Ziegelheim <David.Zi...@rnb.com> wrote:
>> The panhard rod determines the location of the roll centre.
>The problem is the rear axle doesn't know anything about roll center's.
True.
But the sprung mass does. That is what it rolls about.
==
Bob Small
robert haspel
a panhard bar tends, emphasis on tends, to locate the roll center. The car
must be allowed to roll about a point that is natural, ie if a control link
actually fixed the roll center it could cause anti-susspension. I believe
the bar should be in tension, and should be as long as possible to limit
angular changes. A bar running uphill to the outside of the corner, could
tend to hold the left rear off the ground. The wheels must comply with the
track! Use your own head, think for yourself, don't follow the herd!
Dan Pinkham <pink...@nh.ultranet.com> wrote in article
<5bqjtl$k...@decius.ultra.net>...
Robert Small
"robert haspel" <bor...@pdq.net> wrote:
[snip]
> if a control link
>actually fixed the roll center it could cause anti-susspension.
[snip]
Explain please.
What is anti-suspension?
Are you suggesting that a control link configuration that positively
fixed the roll centre would not allow "suspension"?
==
Bob Small
kenned...@gmail.com
that is the roll centre.
With a right side body mount bar, when the car turns left and the body
rolls right, the body mount point drops. The left side (on the axle)
stays at the same height. This gives a _lowering_ of the roll centre.
With a left side body mount bar, when the car turns left and the body
rolls right, the body mount point rises. The right side (on the axle)
The important thing to remember is this: when you run a left frame/right axle tube mounted panhard bar, as the car rolls when you turn left the center of gravity travels closer to the rear moment center, this shortens the moment arm.
Raising the bar makes the chassis resist roll which will loosen the chassis, lowering it increases chassis roll which will tighten the chassis.
When you run the panhard in this fashion it can tend to cause an inconsistent feel of the car because the constantly changing length of your moment arm when cornering.
When you run a left axle/right chassis mounted panhard bar, as the chassis rolls, your moment center travels in relation to your center of gravity, because of the increased movement on the right side of the car when it rolls so your moment arm actually stays the same.
You do not gain or lose roll stiffness during chassis roll, and this provides a more consistent feel to the car.
It is also important that when you adjust the panhard bar, that you center your wheels again, as moving this bar will cause your wheels to track to one side or the other. Unless you don't want your tires to drive your car straight ahead, it is very important to make sure when you do a panhard adjustment to reset your centers.
I recently switched two cars over to the left axle tube/right chassis mount and I can honestly say that the results were very good. A car that was normally 5th place, ended up 18 seconds ahead of 2nd place and was in lap traffic at the end of a heat race, repeated the same performance in the dash, and then for the feature, the track was tacky and could have used a little bit more roll stiffness, finished 2nd place, and a car that normally finished 7th on average took home a 3rd place trophy that weekend too. Both drivers commented on how much more consistent and smooth the car felt after making that change.