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Products in the rear view mirror - Panhard Bars
Panhard/J-Bar centers the rear end on the straights and then applies force laterally as the car transitions into the corner. Based on the height the springs store energy and as we exit the spring energy is released at a rate in conjunction with the Panhard/J-Bar.
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More About Panhard Bars

Adjusting the Panhard Bar or J-Bar always generates feedback from the driver sometimes good and sometimes so bad that the crackle from the driver sounds like the speakers blew at an AC/DC concert. Even on TV you hear about 1/8 adjustments during Cup races that take the driver from waving handfuls of steering wheel to driving with one hand. Of course, the same team can try to cure a small tight feeling and raising the bar the same 1/8 can make the car junk. It seems the entire chassis package revolves around what can be a very sensitive adjustment.

So why is the Panhard/J-Bar so sensitive and how come drivers can nearly always feel even small adjustments? I mean the bar is simple enough - all it does is connect the chassis to the rear housing locating the rear end laterally. Its just a bar with a rod end on each side yet the height and angle seem to do so much.

To help understand why the Panhard/J-Bar is so sensitive it pays to think out all relationships that change based on how it is located. First off, the front roll center gets involved as the roll axis (the line drawn through the front roll center extending through the rear roll center) is affected. As you lower the Panhard/J-Bar you also lower the roll angle and the center of gravity gains leverage because the distance from the roll axis line and the Center of Gravity is increased. The result is a car that rolls more due to the leverage increase and the added distance from the CG allows for roll around an arc with what is basically a larger diameter.

As you raise the roll axis the distance from the Center of Gravity is less and the car rolls less. In this case, there is more of a direct force applied to the right rear tire. Seems so simple yet there is more to think about.

The rear spring rate controls roll so there is a correlation between rear spring rate and the Panhard/J-Bar. In essence, as you run more rear spring the effect of the bar changes or does it? That giant sway bar controls roll as well. All the things that control roll perform their function in a somewhat progressive fashion and the timing of the control is slightly different. This is the point in the story where engineers and data acquisition get fun but since it is always my goal to remove engineering speak here there are many things to consider. Since the variables are many, the answers change depending on entry speed, banking, braking, track grip, tire grip, balance, aero and the like no wonder engineers make the big money and are such snappy dressers.

Whenever I face many dynamic variables that change depending on when and where the car is in the corner it is my goal to find a way to simplify in a fashion that allows me to make real world changes at the track. This is where basic understanding of the hardware can help you to draw your own conclusions.

A low Panhard/J-Bar promotes roll. A high one relatively resists roll. The Center of Gravity in the car is the same regardless if you have 100 lb springs or million pound springs. Springs are progressive. A 500 lb spring compressed one inch stores 500lbs. The same spring compressed 2 stores 1000lbs. So the springs compress in roll and in squat. Great.

The Panhard/J-Bar locates the rear end laterally. In squat it does basically nothing. As an example; a drag car is designed to go in a straight line. The drag car only experiences squat (of course there is engine torque but humor me and imagine just squat). In this example you could mount the Panhard/J-Bar on the roof or on the ground and the squat will be pretty much the same.

In our cars that turn left, the Panhard/J-Bar centers the rear end on the straights and then applies force laterally as the car transitions into the corner. Based on the height the springs store energy and as we exit the spring energy is released at a rate in conjunction with the Panhard/J-Bar. A high bar transfers load quickly and a low one takes longer due to the added distance between the Panhard/J-Bar and the Center of Gravity well at least in an apples to apples situation.

So the result is we can change the timing of roll as well as the loading of the lateral force of the Center of Gravity by adjusting the Panhard/J-Bar. Fabulous but how much and when do we raise the Panhard/J-Bar verses adding more rear spring rate? There is not an answer to this question unless your car has a 48 on the side. In the end, as you have more grip though a better racing surface, tire compound and more down force then a higher Panhard/J-Bar will transfer loads in a more direct fashion creating quick and sporty reactions. Of course track banking and car speed get tossed in the variable bucket too.

If your track is bumpy, worn out, small and has little banking then maybe you want to slow down the reaction of the car and smooth things out with a lower Panhard/J-Bar. Since I grew up in the Northwest all of our tracks were worn out and we raced on top of shiny rocks. I know I ran Panhard/J-Bars at least a full inch lower, on average, than my competition. We managed to win some and we always were good on the long run so in general a lower bar made up for reduced grip and minimal down force as most of our tracks were small and flat.

Tech Tip Courtesy of Joes Racing Products