NiS Open Garage: Charlotte

Headed into Charlotte Motor Speedway I am reminded of something I mentioned in a previous article about iRacing’s setups being tantamount to getting setup sheets from the previous owner when you purchase a race car. At times these setups may require large changes to adapt them to our own driving preferences.

This leads us to two areas where you can make changes to help correct cars that seem out of control. The two areas I am going to focus on this week are basic track bar and spring adjustments. Both of these topics are critical changes we make in NASCAR constantly. Making adjustments in both of these areas can significantly improve cars that seem too far on the loose or tight sides.

When speaking of the track bar you should know that the position of the track bar affects the “rear roll center” of the car which dictates how the weight is distributed from the left side to the right side when cornering. This has a great effect on the balance and handling of the car.

Typically, lowering the track bar will tighten the car, while raising it will loosen it. When “increasing the angle” or increasing the difference in height on one side you change the way the car moves in the corner.

To be more specific, when the right side is mounted higher than the left, the rear tires will be pushed left into the corner. This actually causes the rear wheels to turn right from the way that the rear suspension is mounted in the car.

“The greater the angle, the more it moves” is what I was told.

At first make changes to both sides equally in small increments, then try making very small changes to one side.  Making a small adjustment to the track bar in this week’s setup will help cure the “loose-off” feel and gives us a more stable base to work on.

Small adjustments to the track bar provides a more stable base.

This brings us to our next topic: spring selection. The springs are located at each corner of the car. They are atatched to the lower A-arm and a screw type cup mount on the frame is used to preload the spring and to set ride height. Springs — along with the shocks – are considered to be an art form by many crew chiefs.

iRacing has done a lot of work to keep up with the progressing theories concerning springs. While we were once restricted to springs around the range of 450 lbs. at the low point to 2500 lbs. with the new rules we now see springs of a much wider variety.

This can be confusing to understand for the beginning sim-racer, so we will assume iRacing has the springs close to what the sim likes and focus on the basic adjustments as they are the same no matter the weight of the springs. We will dig deeper into the differing spring/shock/sway bar combination theories in another article.

For general knowledge, stiffer front springs will make the car tighter while stiffer rear springs will loosen the car. Changing the “stagger” or difference will affect the way the car reacts under acceleration and braking.

This week the car seemed tight on entry and to get loose when you got on the accelerator. This gives us a chance to demonstrate how running more spring stagger in the front – with a weaker left side spring – will tighten the car under acceleration (and loosen it under braking). In the opposite, running more spring stagger in the rear, with a weaker left side spring, will have just the opposite effect as the front. Instead of tightening the car, it will loosen the car under acceleration and tighten it while braking.

The more you increase the difference, the more the chassis will respond during these transitions.

Not what you want at Charlotte.

This week we moved the weight forward, used a combination of softer front springs, more camber, and track bar adjustments to create a setup that was fast and stable without sacrificing durability. We tried to find a balance between corner rotation and stability on exit.

Once you have a comfortable balance, use tire pressures to make fine adjustments. You will want to keep four fresh tires and a full tank of gas this week, but be careful not to pit too early.

I have uploaded a more stable base setup in the Open Garage forum based on today’s article that should run okay for the bottom splits. It’s a bit loose “off” to allow the driver to use the throttle to control the turn. While it may need adjusting to run up front, it should help keep a few drivers from self-spinning.

Good Luck and God Speed!

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