NASCAR Cup Series
By Bozi Tatarevic
3 Minute Read
Editor’s note: Bozi Tatarevic is a professional racing mechanic and pit crew member. He will provide technical analysis for NASCAR.com throughout the 2022 season.
Teams have been hard at work to find ways to make the Next Gen car faster, and one of the most notable things we saw in the two practice sessions Wednesday was that some teams appeared to implement reverse skew in an attempt to make their cars faster.
One of the goals of the Next Gen car is to make use of the symmetric body and to have cars look more like what we see on the street, so a rule change was implemented late Tuesday night to reduce that reverse skew. As a result, we will see teams making suspension changes Wednesday.
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Reverse skew is most apparent when cars are traveling down the straightaways as it visually looks like the rear of the body is shifted left while the chassis is pointing straight. The benefit of this configuration, where the car is yawed in a clockwise direction from the top, is that it hides the spoiler from the right rear of the car, which in turn creates the lowest drag configuration. This is an optimal configuration for tracks such as Daytona and Talladega, where drag is one of the main performance differentiators.
— NASCAR (@NASCAR) February 15, 2022
— NASCAR (@NASCAR) February 15, 2022
All of the changes outlined below will require a rework on the rear suspension geometries and setups of the cars that were outside of these new allowable tolerances and will result in seeing cars that visibly show less reverse skew once they hit the track later Wednesday.
Due to the number of required changes, the garage opened at 11 a.m. ET Wednesday as opposed to the original 2 p.m. ET schedule so that teams have plenty of time to make these adjustments before qualifying (8:05 p.m. ET, FS1).
Teams likely achieved this reverse skew by performing adjustments on the rear suspension, where they have options to adjust rear toe and wheel offset by adding or removing shims. Rear toe is the position of the front of the wheel relative to the centerline of the chassis. Toe can be adjusted in multiple methods as there are also slugs that change the position of those toe links relative to the suspension uprights to which the wheels mount.
If we take a closer look at the components that bolt up to that rear suspension upright we can see how shims can be added or removed behind the toe link clevis in order to move that suspension upright in or out. We can also see the toe link slug and how the position of where the toe link connects to the clevis using the slug can affect the position of the upright.
All of these changes result in the change of the rear wheel steer, which basically turns the rear wheels at an angle opposing the body. The specification for the angle of that rear wheel steer has been 0 degrees, but there was previously an allowable tolerance of -0.30 -> 0.30 degrees on the left side and an allowable tolerance of -0.30° -> 0.00° on the right side as measured in pre-qualifying and pre-race inspection. This has now been changed to 0.00° -> 0.30° for both sides in the rear in an attempt to reduce that rear steer angle and visible reverse skew.
Post-qualifying and post-race inspection measurements have also been updated as the previous left side tolerance of -0.55 -> 0.55 degrees and the previous right side tolerance of -0.55° -> 0.25° have now been updated to an allowable tolerance of -0.25 -> 0.55 degrees. While these angles might seem minimal, it is important to note they are measured statically in the inspection station and they grow and become exaggerated when the cars are at speed on track.
In addition to the allowable tolerances being adjusted to reduce the amount of rear wheel steer that teams may attempt, the position of the toe link slugs has also been prescribed for this race weekend. The left rear toe link slug must be set to center or below center while the right rear toe link slug must now be set to center or above center out of the three positions that are available on the slugs, which set the lateral position of the toe link relative to the control arm.