Thanks to a suggestion by reader Anthony Bardoll, I’m happy to present the first in a series of articles on car adjustments. Anthony mentioned that a lot of people do iRacing and have the ability to make the same types of adjustments in their cars that non-virtual race engineers can do. Most of the information available on these adjustments focuses on what happens when you make a change in a particular direction: if you increase parameter x, the car gets looser – but they don’t tell you why. Here’s the ‘why’ for the trackbar.
Trackbar
In 1887, Rene Panhard and Emile Levasor created the car manufacturer Panhard (originally Panhard et Levassor). Panhard is credited with the first modern transmission and provided cars for some of the very first automobile races, like the Paris-Rouen Rally. As part of their R & D effort, they created the Panhard rod, which was used to help make the suspension behave better.
The Panhard bar is a bar connected to the chassis of the car on one end and to the rear end housing on the other end, as I’ve illustrated to the right. The purpose of the trackbar is to control the left-to-right offset of the rear axle. The attachments at the left and right side of the trackbar allow for up and down motion, but not side-to-side motion.
A trackbar has two mounting points – one on the frame and one on the rear-end housing. The position of the mounting on the rear-end housing is usually fixed during assembly of the car. I’ve drawn a slot in the right-hand side of the chassis mount in the rear-view drawing to indicate that you can adjust this position during a race. By raising or lowering the right side of the trackbar, you move the rear axle left or right with respect to the car’s centerline.
Each stock car has three places where a wrench can be inserted during a race: two places in the right-hand side one on the left-hand side. Two of those are for wedge, which I’ll explain in a future column, but this third is a threaded rod that raises and lowers the trackbar mount. Usually clockwise turns lower the track bar while counter clockwise turns raise the track bar. If you raise the trackbar on the right-hand side, you move the rear wheels to the right. This makes the car looser when accelerating and tighter when braking. Conversely, moving the trackbar down on the right-hand side pushes the wheels to the left, tightening the car under acceleration and loosening the car during braking. Moving the rear axle left/right is essentially adding stagger (“rear steer”) to the car because the distance between the front and rear wheels isn’t the same on both sides of the car due to the offset.
During a race, only one side of the trackbar gets adjusted; however, you can change the height of both sides of the trackbar when you’re initially setting up the car. The overall up-and-down position changes the weight distribution and thus the way the body rolls when the car goes around a corner. If you raise both ends of the trackbar, you make the rear roll center higher and the car gets looser. If you lower both ends of the trackbar, you lower the rear roll center and the car gets tighter.
The trackbar itself is generally 1-1/4 to 1-1/2 inches in diameter and it’s essentially just a long bar with Heim joints on the ends.
I hope that gives you an idea of what’s happening when you hear the announcer talk about trackbar being adjusted during pit stops on Sunday!
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I don’t understand how moving the rear-end left or right changes the distance between the front and rear tires. Help? Thanks, D.
I love this stuff – thanks for sharing! The only dot that I am not connecting is why moving the rear wheels to the right loosens the car under acceleration/tightens it under braking, etc. Does it have to do with balance, weight distribution? I am curious as to why it has that affect.
Nice article! Love understanding a little bit of the science of NASCAR and follow you on Twitter to make sure I don’t miss anything. Thanks!
Thanks! I will try this out on NTG and see what it does. Usually I make adjustments with absolutely no idea what it means.
If you go from a 3” offset to a 2” on right rear , you pulled the rim and tire out .that will loosen the car . Do the same thing on left rear ,it will tighten car.