We are into the second half of the 2014 NASCAR iRacing Series as we pull the trailer into Michigan International Speedway. By now you should be familiar with most of the common changes we can make to the chassis of a race car to adjust its handling, control its temperatures and increase its speed off the corners and through the straights.
The base setup is inherently loose and with ambient temperatures in the eighties, it’s like driving on ice. So the first adjustments you may want to make here, drawing from our previous lessons, are to lower the track bar, soften the springs and increase the forward weight distribution.
Seeing as we are at a speedway this week, it seems an appropriate time to discuss aerodynamics and how your setup will affect the car in and out of the draft. We will discuss our theory on using a combination of lower ride height, the right amount of tape and softer shocks/springs to create a setup that handles well in and out of the draft, has speed off the corners and runs consistent lap times.
The first order of business is how to lower your car. Decreasing ride height reduces drag from air moving under the car and therefor increases speed. The trick however is to get enough play in the suspension to allow the front end to dive in the corners and remain “sealed” through the turn without bottoming out. We use a combination of the right spring/shock settings in addition to lowering the car to the lowest we can get it (especially in front) to try and “seal” the front and side skirts creating even airflow around the car.
We accomplish this task by adjusting the “spring perch.” Take note of the ride height as you make adjustments. Count the amount of “clicks” you make and make equal adjustments to the fronts and rears as pairs. You will want to “step” the car down, first at the front and then at the rear slowly bringing the car down yet monitoring the setups to know your limits. This is similar to real life as we always “count the turns” we make on a spring perch and keep note of it. Once set we will use a grease pen or similar implement to mark the position.
Keep in mind that as you adjust the car, uneven adjustments will have adverse effects on the handling. If you lower the car equally in steps you should not notice much difference in handling or wear as you are not changing the “cross weight” of the car. You are simply lowering the height.
As you lower the front suspension you increase the cross weight (shift the center of gravity towards the front) of the car. When you do this the car will tighten especially on exit (where we need it this week). Moving the weight ballast forward or increasing the split between the front and rear ride heights will also have this effect. Knowing this can help us to make educated changes to a car where we like the springs and shock settings but want to make minor adjustments to the car’s handling.
“Keep in mind that as you adjust the car, uneven adjustments will have adverse effects on the handling.”
Keep in mind that cars run loose in the draft due to a reduction of air over the rear spoiler. Try and get some practice in traffic with your setup so you know how it will react.
Working with the base Michigan setup we are going with softer springs in an effort to provide adequate suspension travel for the skirts to “seal” at speed. The car will want to over-rotate on exit even if you lower the track bar, so try less rebound in the right rear shock. This will help the the right rear tire retain traction on exit.
That being said you will want to keep note of the status of the tires and make a camber adjustment on the left front to help control the temperatures. If you need to reduce the camber in the left front remember that doing such will tighten the car middle out (of the turns) and you may need to make another adjustment to compensate for this.
One last note before we close this week: watch your oil and water temps. If you run close to the line you might find yourself overheating in the draft or in the event of front end damage. I find it better to run a few degrees conservative as aero is important here but not as much so as it is at Daytona or Talladega. Fresh tires and a good fuel strategy should prove useful this week.
The setup I will be using this week is available in the NiS Open Garage forum and as always Good Luck and God Speed!