NASCAR will switch to a single lug nut for fastening its tire and wheel assemblies in Cup cars next season, ending decades of using a renowned five lug nut pattern.

An official told NBC Sports the move was driven by the new 18-inch aluminum wheels (3 inches bigger than the current wheel) that will be used with the NextGen car, which will make its debut with the 2021 season, and are intended to increase product relevance for manufacturers.

According to engineering analysis, NASCAR senior vice president of innovation John Probst said the durability of the new wheels decreases by 30 percent with five lug nuts.

“The answer became pretty clear that we needed to go single lug nut,” Probst said. “And I know that a lot of folks might say, ‘Well, if product relevance is your main goal, name me a car that has a single lug nut.’ I’m not sitting here saying I could, but I can name lots of cars that have 18-inch aluminum wheels. And that once we decided 18-inch aluminum wheels was the primary driver, the engineering solution was pretty clear.

“It’s almost never the case that all five lug nuts are literally tight to the wheel, and if we don’t have five lug nuts tight to the wheel, the durability of an aluminum wheel drops. If all lug nuts could be guaranteed tight, five is a workable solution. With the pressure to do a very fast pit stop, I can’t say that we have knowledge that all five are ever completely 100% tight to the torque spec.”

Because of a higher torque, the pit gun will be applied longer to a single lug nut vs. five but still will take a shorter amount of time. NASCAR estimates that it will take roughly 0.5 seconds to remove the single lug (and the same time to reapply) vs. the 0.8-1.0 second for a top-flight tire changer removing five lug nuts (and running the pattern back on in the same time). So the move could drop four-tire pit stops consistently into the 10-second range.

Probst said most Cup teams are in favor of the move, which NASCAR hopes will allow teams to use wheels in multiple years (instead of multiple races with the current steel wheels). There has been some pushback from teams that cite the competitive advantages from investing money and time for training crews to change five lug nuts.

There also has been speculation on how such a move might impact the value of tire changers.

Unlike other racing series that use single lug nuts and allow tire changers to be in place before the stop (such as IndyCar), NASCAR is keeping the same pit stop procedures with a single lug nut. Probst said the choreography of scrambling from the right to left side should keep pit crew members in demand as highly skilled athletes who are among the most well-paid team members in NASCAR.

“Nobody’s done it, so I’m not sure anyone can have an informed opinion on how it’s going to affect them,” Probst said. “But there’s still a premium on getting from the pit wall to the right hand side of the car. That’s not going to change. You’re still going to have to get the nut off and back on as quickly as possible. That’s not going to change. You’re going to have to go from the right hand side to the left hand side of the car as quickly as possible.

“The amount of the time on a lug nut today is less than a second, but the time from the right hand side to left hand side is much more than that. So shaving off the time from the left to right side is going to have a bigger impact. I don’t anticipate myself in the near future changing tires. You’re still going to have a massive premium on speed because that’s going to determine the length of your pit stop. They’re still going to be professional athletes.”

Other notable elements from the move to a single lug nut:

–There will be no more postrace lug nut checks or lug nut penalties.

–Because the lug nut will be retained in the socket, the change from five lug nuts will end the practice of gluing lug nuts to the wheels, which will cut down on prerace preparation time (thousands of lug nuts are glued to wheels before races over the course of a season). It also should save time for practicing stops as teams could rotate a few sets of wheels instead of needing to glue lug nuts on a dozens of sets for a pit crew training session at their shops.

–Teams should be replacing wheels less often because five lug nuts deliver more of a pounding than a single lug nut – particularly when they aren’t tight and the wheel wobbles (which can cause the lug nut holes to deform). Aluminum also is less forgiving than the previously steel wheels, making a switch to a single lug nut more logical.

–The single lug nut will be used for the first time Monday and Tuesday during the NextGen test at Auto Club Speedway (with William Byron). But there will be no pit stops simulated under race conditions at the test.

–NASCAR has no plans to adjust pit crew or roster sizes. Though the tire and wheel assembly will be lighter, it won’t be in a significant measure that affects how the tires are delivered to the car.