The minimum clearance between the ground and the bottom of the body of the side panels (called the side skirts because they are extensions of the side panels) will be 4.5 inches on the right side and 5 inches on the left side, according to a NASCAR technical bulletin issued Wednesday.
At the start of the year, the clearance was 3 inches on each side. Last month, NASCAR increased the clearance by an inch on the right side of the car and 1.5 inches on the left.
The changes, which go into effect with the race next week at 1.5-mile Kentucky Speedway, are designed to decrease side downforce and increase the ability of drivers to race side-by-side.
Five-time Cup champion Jimmie Johnson said the change will decrease downforce but he is unsure of the impact.
“It's just a tough dynamic to try to make the lead car in clean air drive as poorly as somebody in dirty air,” Johnson said. “I appreciate the process. I know we're trying to create better racing, side-by-side racing on the mile-and-a-half tracks, but the aero deal is tough to get around.
"I don't know what the answer is. I don't feel this is it. I appreciate and respect the effort being made.”
Former crew chief Larry McReynolds, now a TV analyst for Fox and Speed, said the change may enhance passing.
“I’m not convinced anything is ‘broken’ on these cars because we’ve had 11 different winners in 15 races this season," he said. "But all the teams are trying to get to where they can better pass another car if they’re faster and can catch him. My guess is this latest side-skirt change likely will take some of the aerodynamics away from these cars, making them less aero-dependent and therefore possibly more able to pass another car when faster.”
NASCAR also changed the requirements of the rear sway bar. The rear sway bar connecting link must be perpendicular to the ground at any angle at ride height.
NASCAR changed the rule to regulate how teams use sway bars to ensure they are being used as anti-roll bars as cars go through the corners. Typically, NASCAR wants to avoid teams using sway bars like another shock or spring in the car.
Source: Sporting news.com