The Panhard bar (also called a track bar or lateral locating bar) is a critical component of the rear suspension on most quarter midgets and karts. Understanding how it works and how to adjust it can have a major impact on your car's handling.
What is a Panhard Bar?
A Panhard bar is a lateral locating link that connects the rear axle to the chassis. It controls side-to-side movement of the rear end, keeping the axle centered under the car while allowing it to move up and down with suspension travel.
One end attaches to the chassis, the other to the axle.
It runs sideways across the car, typically at an angle.
The bar is mounted with rod ends (heim joints) at both ends, allowing it to pivot. It's usually positioned on the left side of the car, connecting the left side of the chassis to the left side of the axle, but some cars use a "Z-bar" or other variations.
Why is the Panhard Bar Important?
The Panhard bar performs several critical functions:
- Locates the axle laterally: Prevents the rear axle from sliding side to side.
- Determines roll center: The height and angle of the bar help establish the rear roll center, which affects weight transfer and handling.
- Influences side bite: Adjustments can increase or decrease traction on the left or right rear tire.
- Controls chassis roll: Works with springs and shocks to control how much the chassis rolls in corners.
Panhard Bar Geometry
The key geometric factors of a Panhard bar are:
| Term | Definition | Effect |
|---|---|---|
| Bar Height | How high the bar mounts on the chassis and axle | Affects roll center height and side bite |
| Bar Angle | The angle of the bar relative to horizontal | Determines how much the axle moves laterally during suspension travel |
| Bar Length | The distance between mounting points | Longer bars create less lateral movement, shorter bars create more |
Roll Center Height
The Panhard bar is a primary determinant of the rear roll center. The roll center is the imaginary point around which the chassis rolls in corners. A higher roll center creates more jacking effect and can increase side bite, while a lower roll center reduces jacking and can make the car feel more stable.
Higher Roll Center
- More side bite (traction)
- More jacking effect (can make car tighter)
- More responsive to bar adjustments
Lower Roll Center
- Less side bite
- Less jacking effect (can make car looser)
- More stable, less reactive
Adjusting the Panhard Bar
Most Panhard bars have adjustable mounting points on the chassis and/or axle. Here are the common adjustments and their effects:
1. Changing Bar Height
| Adjustment | Effect on Handling |
|---|---|
| Raise chassis mount (bar angles down to axle) | Increases roll center height, more side bite, can make car tighter |
| Lower chassis mount (bar angles up to axle) | Decreases roll center height, less side bite, can make car looser |
| Raise axle mount | Similar to raising chassis mount, increases roll center |
| Lower axle mount | Decreases roll center, reduces side bite |
2. Changing Bar Angle (Preload)
Some Panhard bars are adjustable in length, allowing you to preload the suspension. This is done by shortening or lengthening the bar, which pushes or pulls the axle sideways relative to the chassis.
Shorten the Bar
Pulls the axle toward the chassis mount side (usually left). This increases load on the left rear tire, which can:
- Increase left rear bite
- Make car tighter if excessive
- Help on slick tracks
Lengthen the Bar
Pushes the axle away from the chassis mount side. This reduces load on left rear, which can:
- Decrease left rear bite
- Make car looser
- Help on high-grip tracks
Note: Preloading the Panhard bar also affects cross weight. Shortening the bar (pulling axle left) will increase cross weight slightly. Always check your scales after making preload adjustments.
Baseline Panhard Bar Settings
Every chassis is different, but here are general starting points for quarter midgets:
| Parameter | Baseline Setting |
|---|---|
| Chassis Mount Height | 8" to 10" from ground (measured at frame rail) |
| Axle Mount Height | 8" to 10" from ground (measured at axle centerline) |
| Bar Angle (static) | Parallel to ground or slightly down to axle (0° to 3°) |
| Preload | Zero preload (bar length adjusted so axle is centered under chassis) |
Panhard Bar and Track Conditions
Here's how to adjust your Panhard bar for different track conditions:
| Condition | Recommended Adjustment |
|---|---|
| Slick, dry track (low grip) | Raise roll center (higher mounts) or add preload (shorten bar) to increase left rear bite |
| Tacky, high-grip track | Lower roll center (lower mounts) or reduce preload (lengthen bar) to prevent tightness |
| Car is tight (push) off corners | Lower roll center or reduce preload (lengthen bar) |
| Car is loose (oversteer) off corners | Raise roll center or add preload (shorten bar) |
Common Panhard Bar Mistakes
- Binding: Ensure rod ends are free and not binding through suspension travel. Binding causes inconsistent handling.
- Incorrect roll center height: Too high can make car unpredictable; too low can reduce side bite too much.
- Excessive preload: Too much preload can cause the car to feel "jacked up" and lose traction.
- Ignoring geometry: As suspension moves, the bar angle changes. Make sure your setup works through the full range of travel.
Measuring and Checking
To check your Panhard bar setup:
- With car at race weight on level surface, measure chassis and axle mount heights.
- Check that bar is parallel or slightly angled as desired.
- Disconnect one end and check that it moves freely without binding.
- Cycle suspension up and down to ensure no binding occurs.
- Check that axle is centered under chassis (measure from chassis to axle on both sides).
Summary
The Panhard bar is a simple but powerful tuning tool. By understanding how its height, angle, and preload affect handling, you can dial in your rear suspension for any track condition. Start with baseline settings, make small adjustments, and keep detailed notes.
For more information on related topics, see our guides on Basic Chassis Set Up, Cross Weights Explained, and Track Side Chassis Adjustments.