Publisher’s Note: Hey Racefans- Former Germain Racing mechanic and aspiring NASCAR writer Patrick Reynolds takes us inside the garage today to help us better understand some of the adjustments made on a car in the middle of the race. On this occasion, Patrick explains track bar adjustments. We welcome interaction here, so feel free to ask any questions you may have.
An earlier column of mine addressed wedge in a stock car chassis. I wrote about how the race car was set up in the shop and the adjustments made on pit road during a race. (To read that article, go to “Archives” on the lower right of this page, click on January, 2009 and then click on the 20th).
One of the other common chassis changes made during the race is the raising and lowering of the track bar. Like the wedge, some fans might wonder exactly what it is and what does it do? Let’s address this in today’s article.
The track bar is also sometimes referred to a panhard bar. Either term is accurate and acceptable. The bar locates the rear end housing within the chassis left to right. The location is one of the items we work on during the set up process on the surface plate. All four wheels are located in tandem, but for today we will discuss the rear.
A track bar is a hollow steel tube approximately one and three-eighths of an inch in diameter. The length is adjustable and this moves our rear end housing from left to right. During pit stops the height of the bar’s mounting location on the chassis is what the crew works on.
The left side of the track bar has a three-quarter inch heim joint, or rod end, threaded into the end. The threads are also of the left handed variety, or opposite of what most of the world is used to, for a very important reason which we will get to.
A three-quarter inch bolt attaches our bar’s left side to the truck arm, sometimes called a trailing arm, which is the I-beam that bolts to the chassis center section and on which the rear housing sits.
The right end of the bar bolts to a bracket and slider mechanism welded to the framework. This is usually directly in front of the fuel cell and right behind the wheel location. The right end of the bar holds an identical heim joint except for the threads. This set is threaded to the right. Why? So the track bar can be turned and the location of the rear will shift from left to right.
With one end firmly attached to the chassis and the other attached to our rear assembly, by spinning the bar, the housing will come closer to the attached frame point or move farther away. The key is having the left handed threads on one end and right handed threads on the other. Our bar’s overall length grows or shrinks, depending on which way we turn it. This is set in the shop or garage area and is not an over the wall adjustment.
The slider is attached to the extension that lines up with our adjuster hole in the rear glass. This is what fans see a pitcrew member turning on television. A ratchet and extension tool is inserted through a hole in the rear glass into the top of a threaded extension connected to our slider. Clockwise turns lower the track bar while counter clockwise turns raise the track bar.
The force in the turns from the left side of the car is pushing through the track bar to the car’s right side. The difference is how tall on the chassis the force is applied.
Picture trying to tip over a chair in your house. If you push on the bottom of the legs, there is not much leverage to tip it over. Now push on the top of the chair and there is the leverage to tip it over. The laws of physics still apply to a stock car.
On a left hand corner raising the track bar will apply a force higher up. Lowering the track bar lowers the point of our force.
For oval track applicable reasons, when a crew chief calls for raising the track bar, the car is tight and he is attempting to loosen the driver’s feel. The opposite is also true. By lowering the track bar, the feel will tighten up. Used in a loose condition.
And as a general rule of thumb the track bar is looked at when tackling problems from the middle of the turn through the exit.
Now when we are racing at Infineon and Watkins Glen…. Oh, I’ll save that for another day.