NASCAR implements aero rules changes for Michigan and Kentucky

In addition to previous rules announcements related to welding truck arm mounts and the removal of downforce generating electric fans, NASCAR will implement the following rules changes for the upcoming Cup races at Michigan and Kentucky.

Reduce skew generated side-force by setting rear toe to zero (same rule used in All-Star race).
Aero package tweaks to reduce aero generated downforce and sideforce.
Spoiler shortened from 3.5 inches to 2.5 inches.
Splitter reduced to 2 inches
Resize of deck fin to match spoiler.

NASCAR officials said all of the changes were developed after going through an extensive process of gathering ideas from within the industry, evaluating them and identifying ways to continue to improve the rules package this season.

The goal of the rules changes is to decrease downforce by additional 500 pounds (about 15%) and side force by 125 pounds from the 2016 package already in place.

"We took a lot of downforce off last year but we put a lot of grip in so the corner speeds came down (some) but didn't come down a lot," Gene Stefanyshyn, NASCAR's vice president of innovation and racing said Thursday at NASCAR's research and development center in Concord, N.C.

"In that journey, what happened is we mixed up the tires and increased the fall-off. So, we got the fall-off we wanted and got some of the speed out but got some back with the grip. Now we're at the point where we take this (corner) speed out."

Asked how NASCAR factors in the amount of downforce teams work to restore during the season, he said, "We on occasion take cars and go measure them. In the past we hadn't done that much. We have a model but we know in a year or so our model is changed, so a couple times a year we take some cars and take them to the wind tunnel and update our baseline.

"We want to see where the industry has gotten. So, we have a pretty good idea what the teams have out there by measuring the cars. We need to understand it or we're going to be off a bad baseline."