The toy car is back out so I can discuss my best interpretation of the #48 disqualification last night.
Before we get to the penalty and the what they likely found we need to first understand the goals of the teams with skew and how they use rear toe. This picture shows the direction that NASCAR wants which is towards zero toe. Rear wheels point straight when the car does.
Toe is the measurement of the wheels from side to side. If the wheels measure the same across in the front and rear and in the same direction they have zero combined toe. We can also measure individual toe for each wheel based on a reference point.
When we zoom in on the individual wheel we can see a comparison of how zero toe versus toe-in or toe-out may look in the back of a car.
So if we look at our picture with zero toe again we can see that it’s terrible for aero because the car is going straight and the air is passing right by it.
But lets introduce some toe changes in the rear now to tilt the car sideways while still being able to keep the wheels straight. This is known as skew and is familiar to many.
Now that we have made those toe changes the car is pointed sideways so the air is hitting the quarter panel and the rear spoiler and the car can take advantage of all the fancy aero work that the team has done. The wheels are still going straight because of those toe changes.
NASCAR measures these toe specs before and after the race and the teams have a window to work in and try to maximize it. One of the ways that they make these tow changes is with the truck arms and how they mount. Let’s imagine that these pieces of wire are the truck arms.
Based on feedback from some smart people I know that teams have figured out how to build these truck arms and the way they mount in order to maximize that toe which results in maximized skew like the example above. This is a model car photo but shows kind of how they mount.
So getting back to the penalty on the 48 car, it is likely that they engineered their car to take advantage of these optimizations to maximize skew and at some point during the race something broke or moved that caused the toe measurement to change.
While I mention the truck arms above because they have been a recent focus in development, the rear toe is affected by many other suspension components in the rear and can change with any type of impact or even if the material changes shape due to something like heat.
It is also possible that one of the wheels was bumped during the race from contact or something similar which could bend a component behind the wheel causing that toe measurement to change.
My general consensus is that the team likely did not design a part to fail but instead they designed it to be optimal and at the bleeding edge of performance and some outside factor took it over the edge and caused it to fail.
Hopefully this helps to explain it a bit and show why the OSS might show different measurements at the beginning of a race and at the end of a race for a car and why teams would want to try to optimize design and chassis setup in that direction.
Based on the statement from @DanielsCliff I am going to lean in the direction of something breaking and say that I don't believe that they did anything nefarious on purpose. https://twitter.com/DanielsCliff/status/1264797660927623169?s=20
Hopefully the takeaway is that the NASCAR tech officials are doing their job and not that there is some conspiracy as well as the fact that @DanielsCliff and his team are really smart and figured out a way to optimize the car and likely found the edge of the modifications now.