Effects of Front Roll Center Adjustment

Front roll center has most effect on on-throttle steering during mid-corner and corner exit.

LOWER front roll center

* More on-throttle steering

* Car is less responsive

* Better on smooth, high grip tracks with long fast corners

HIGHER front roll center

* Less on-throttle steering

* Car is more responsive

* Use in high grip conditions to avoid traction rolling

* Use on tracks with quick direction changes (chicanes)

Effects of Rear Roll Center Adjustment

Rear roll center affects on- and off-throttle situations in all cornering stages (entry, mid, exit)

LOWER rear roll center

* More on-throttle grip

* Less grip under braking

* Use to avoid traction rolling at corner entry (increases rear grip)

* Use under low traction conditions

* Increases traction, reduces rear tire wear

HIGHER rear roll center

* Less on-throttle steering

* Car is more responsive

* Use in high grip conditions to avoid traction rolling

Height
The 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

Raising the 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!

When adjusting 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. Generally, a 1/4" change to the height of a panhard bar makes a noticeable change in handling on dirt race cars (asphalt cars = 1/8").

Angle
During cornering the chassis exerts a side force on the rear axle and tires through the panhard bar . 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.

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 = 1/8"). 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 . 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 axle--Read on!

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.

Generally, a 1/4" 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.

Tuning Tips

-- Recommended starting points

Height : Use chassis builders recommendation or start with the panhard mounted at  the centerline of the axle.

Asphalt - level.

-- A high panhard bar works best on fast race tracks & on heavy race cars.

-- If your panhard bar is mounted too high you can expect:

• Loose corner handling (usually)
• Little chassis roll
• 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 handling (usually)
• Excessive chassis roll
• The chassis to be sluggish and unresponsive to the driver.

-- If adjusting the panhard bar angle to the maximum recommended rake does not completely cure a handling problem, lower the whole bar to tighten handling or raise the whole bar to loosen handling.

-- 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.