height of the panhard barhelps to determine the height of the rear
roll center(see illus. 1). The roll center is an imaginary point
around which the rear of the race car rolls. The height of the rear
roll center (and the front also) is critical to handling. When you
lower the panhard bar the rear roll center drops. A lowered rear
roll center promotes side bite at the rear which tends to tighten
corner handling. However, an extremely low roll center can generate
excessive chassis roll which can cause suspension geometry problems.
Also, excessive roll can delay corner exit acceleration.
center moves downhill whenever the angle of the panhard bar is
increased and uphill under opposite conditions.
center moves towards a stiffened and away from a softened side
of the rear suspension.
a short panhard bar is used and installed with alot of rake, the
rear roll center may be located beyond the panhard's mounting
points (as shown in illus.2).
panhard bar raises the rear roll center. Generally, this adjustment
causes corner entry handling to loosen and chassis roll to lessen.
You can learn the "tuning range" for heights of your panhard
bar by testing at the race track and taking good notes!
for height, change both ends of the panhard bar. Otherwise you may
introduce another handling effect by changing the angle of the panhard
bar (more later). Also, if you adjust the height of the panhard
bar just at the chassis, the rear roll center may move in the opposite
direction(see illus. 1&2). Generally, a 1" change to the
height of a panhard bar makes a noticeable change in handling on
dirt race cars (asphalt cars = 1/2").
is typical of many dirt cars using a panhard bar mounted to the
axle near the pinion gear. if the rear roll center occurs outboard
of the panhard's mounts (as shown above), raising the panhard
at the chassis will lower the rear roll centers and tighten corner
handling! the opposite adjustment gives opposite results.
the chassis exerts a side force on the rear axle and tires through
the panhard bar (see illus. 3). When the panhard bar is level, it
transmits a wholly lateral force to the rear tires. However, when
the panhard bar is angled downward to the right, it transmits a
partially downward force to the rear tires and rear traction is
enhanced. Conversely, when the panhard bar is angled upward to the
right, it transmits a partially upward force to the rear tires and
rear traction is lessened. The effect of an angled panhard bar on
rear tire loadings is brief but very important handling.
the chassis exerts a force to the axle through the panhard bar.
The load effect on the axle is dependent on the angle of the panhard
- axle is loaded (briefly)
position "b" - no affect on axle's load
position "c" - axle is unloaded (briefly)
NOTE: the effects of angle are the same for panhard bars mounted
to left or right side of the chassis. each rear tire is affected
in proportion to each tire's distance from the panhard's axle
mount points.(see illus. 4)
You can increase
the panhard bar's effect on tire loadings by increasing the static
upward or downward angle of the panhard bar. However, too much panhard
bar angle can cause drastic changes in rear tire loadings during
cornering and handling may become erratic as a result. Generally,
a 1" change to the difference in mounting point heights of
the panhard bar makes a noticeable handling change on dirt race
cars (asphalt cars = 1/2"). A good rule of thumb is to keep
the height difference of the panhard bar mounts to within 10% of
the panhard bar's length (for example: 20" panhard bar = 2"
maximum mounting height difference). When making changes to the
angle of your panhard bar, be aware of any effects to the height
of the rear roll center.
In order to
determine the ultimate handling effects of the panhard bar's angle,
one must consider where the panhard bar is attached to the rear
The forces transmitted
through by the panhard bar are applied to the rear axle at the panhard's
axle mount point. The lateral location of the mount on the axle
determines how much each associated rear tire is loaded or unloaded
by the panhard bar during cornering (see illus. 4).
ANGLE AFFECTS LR MOST
B. PANHARD ANGLE AFFECTS LR & RR EQUALLY
C. PANHARD ANGLE AFFECTS RR MOST
THE ANGLE OF THE PANHARD BAR CAN AFFECT THE INITIAL LOADINGS OF
THE REAR TIRES (SEE TEXT). THE DEGREE OF THE EFFECT ON EACH TIRE
IS DEPENDENT ON THE LATERAL LOCATION OF THE PANHARD'S AXLE MOUNT
If the panhard
bar is attached to the rear axle near the center of the rear tire
track*, the panhard bar will load or unload both rear tires by a
similar amount during cornering. With this arrangement you can increase
rear traction, hence tighten handling throughout the corner, by
increasing the downward or decreasing the upward (to the right)
angle of the panhard bar. You can loosen handling throughout the
corner by making adjustments opposite to those listed above.
If the panhard
bar is not attached to the rear axle near the center of the rear
track, the panhard bar will load or unload the rear tires unevenly
during cornering. The closer a tire is to the panhard bar's axle
mount the greater the tire is affected by the angle of the panhard
bar. Conversely, a distant tire is affected less by the angle of
the panhard bar.
6" change in the lateral location of the panhard's axle mount
point makes a noticeable handling change. You should keep the following
in mind when adjusting the panhard's angle or its lateral location
on the rear axle: *Any increase in the load of the RR tire and/or
decrease in the load of the LR tire tends to tighten corner entry
and loosen corner exit handling. *Any decrease in the load of the
RR tire and/or increase in the load of the LR tire tends to loosen
corner entry and tighten corner exit handling. *Increasing the load
of the rear tires equally tends to tighten overall corner handling.
*Decreasing the load of the rear tires equally tends to loosen overall
corner handling. *Adjustments to the panhard bar primarily affect
corner entry and mid-corner handling.
By now you should
have a good understanding of how some of the design elements and
tuning adjustments of a panhard bar have a collective effect on
handling. If anything you have read is unclear, go back and reread
the article before progressing.
A panhard bar
that is attached to the right side of the frame lowers during chassis
roll. However, a panhard bar that is attached to the left side of
the frame raises during chassis roll. However, the effects on handling
of a right side versus a left side frame mounting are not always
predictable. The location of the panhard's axle mount can counteract
any predictable handling effects. The current tendency is to mount
the panhard to the left side of the dirt car chassis and to the
right side of asphalt chassis.
roll a short panhard bar changes its angle, hence handling, more
radically than a long panhard bar. Consequently, handling can become
inconsistent if the panhard bar is too short (20" minimum length
is recommended). Generally the length of the panhard bar is determined
by the desired location of the panhard's axle mount.
reasons, the panhard bar is generally mounted behind the rear axle
whenever a long panhard bar is desired. Also, a rear mounting provides
more potential mounting positions than a front mounting. Keep in
mind that since the roll axis (an imaginary line connecting the
front and rear roll centers) is usually inclined to the rear, a
rear mounted panhard bar must be positioned higher than a front
mounted panhard bar in order to maintain a given roll center height.
A front or rear
location of the panhard bar makes little difference on cars equipped
with solid rear suspension linkages. However, this is not the case
for cars equipped with torque absorbing devices (5th coils, 6th
coils, etc.) These devices allow the axle (pinion side) to wrap
(rotate) downward during deceleration and upward during acceleration.
During axle wrap, the height of the panhard's axle mount point changes.
Consequently, both the angle and height of the panhard bar change
during axle wrap and handling is affected.
of the panhard's axle mount (ahead of or behind the axle), determines
whether the mount will move up or down during deceleration or acceleration.
During deceleration, the panhard's axle mount point drops if the
mount is ahead of the axle but raises if the mount is behind the
axle. During acceleration the height of the panhard's axle mount
point changes opposite to those listed above.
For tight corner
entry handling, the panhard bar should be mounted to the front of
the axle. This arrangement causes the panhard's axle mount point
to drop during deceleration. Consequently, the height of the rear
roll center drops & rear side bite is enhanced. Also, if the
panhard is attached to the left side of the chassis the angle of
the panhard bar changes during chassis roll so to increase rear
traction and further tighten handling during deceleration.
the panhard bar is attached to the rear of the axle the panhard's
axle mount point raises during deceleration. Consequently, the rear
roll center raises and corner entry handling tends to loosen as
a result. Also, if the panhard is attached to the rear of the axle
and the left side of the frame, the angle of the panhard bar changes
during chassis roll so to reduce rear tire loadings and further
loosen handling during deceleration.
of axle wrap on the panhard bar appear to influence corner exit
handling to a lesser degree than corner entry handling. At this
point, you should be able to analyze any effects the panhard bar
may have on corner exit handling.
It should be
mentioned that during cornering, a front mounted panhard bar resists
axle wrap-up (acceleration) and enhances axle wrap-down (deceleration)
whenever the panhard bar is angled downward to the right. A rear
mounted panhard bar gives opposite effects. However, the effects
to handling appear to be minimal.
a complete line of high quality panhard bars and mounts that are
designed to provide the geometry needed for superior handling. Hopefully,
the parts that we build and the information that we provide will
enable you to "Experience the AFCO Advantage!"
Recommended starting points
builders recommendation or start with the panhard mounted at,
or up to 2" below, the centerline of the axle.
Dirt - 1"
downhill to the right.
-- A high panhard
bar works best on fast heavy race tracks & on heavy race cars.
-- If your panhard
bar is mounted too high you can expect:
- Loose corner
- Little chassis
- The chassis
to be unforgiving and overly sensitive to the driver.
-- A low panhard
bar works best on slick race tracks and lighter race cars.
-- If your panhard
bar is mounted too low you can expect:
- Tight corner
- The chassis
to be sluggish and unresponsive to the driver.
-- If adjusting
the panhard bar angle to the maximum recommended rake (10% of the
panhard's length) does not completely cure a handling problem, lower
the whole bar to tighten handling or raise the whole bar to loosen
-- If your rear
axle steers towards the outside of the race track during chassis
roll (loose steer), a lowered panhard bar (which increases chassis
roll and normally tightens handling) may actually loosen handling.
Conversely, a raised panhard bar (which decreases chassis roll and
normally loosens handling) may actually tighten handling.
-- The shape
of a panhard bar has no effect on performance. The mount locations
are what makes a difference.