NASCAR is making big changes in its top Cup Series with the redesigned Next Gen race car set to debut in 2021. One of those changes will be a wheel design that brings NASCAR closer to other race series.

The Next Gen car will use a single-lug, center-locking 18-inch aluminum wheel from BBS, replacing the current 15-inch steel wheels, NASCAR said Tuesday.

The current steel wheels have a five-lug design, closer to what is used on road cars. While most road cars do not have center-locking wheels, the Next Gen wheels' aluminum construction and 18-inch diameter is more relevant to production vehicles than the 15-inch steelies, John Probst, NASCAR senior vice president of innovation and racing development, said in a statement.

Center-locking wheels are common in other forms of racing. The setup streamlines tires changes, since crews only have one lug per wheel to keep track of. But NASCAR doesn't expect the new wheels to change the execution or speed of pit stops.

NASCAR Next Gen race car prototype

NASCAR Next Gen race car prototype

"I think from a fan standpoint, the choreography of the pit stop will look unchanged," Probst said.

Pit crews will still go over the wall when a car pulls up to the box, rather than waiting in the box, as in Formula One, Probst said. The five-person limit on crew members who go over the wall will also remain unchanged, he said.

Because the new wheels require more torque to fasten, crew members will have to hold air guns to the wheel longer, Probst said. So total pit stop time will likely remain unchanged, he predicted.

The new wheels were used in the fourth test of Next Gen prototypes at Auto Club Speedway in Fontana, California. Previous tests using aluminum wheels with the old five-lug design were conducted at Richmond Raceway, Phoenix Raceway, and Homestead-Miami Speedway.

NASCAR Next Gen race car prototype

NASCAR Next Gen race car prototype

NASCAR has been tight lipped on other details of the Next Gen car, but Hagerty reported in December 2019 that the new race car will feature a revamped transmission and rear suspension. The tried-and-true H-pattern 4-speed manual will be replaced with an Xtrac sequential gearbox, according to Hagerty. The gearbox could also end up packaged as a transaxle at the back of the car.

A transaxle will yield better weight distribution, but will also require NASCAR to scrap its current solid-axle rear-suspension design, Hagerty noted. The Next Gen will likely have independent rear suspension as a result.

As with the wheels, these changes will help bring NASCAR up to date with other race series. While NASCAR does not portray itself as a testbed for new technology, racers have likely reached the limit of wheel, suspension, and transmission designs that can be traced back to the 1960s. If nothing else, the Next Gen car offers a fresh challenge for engineers and drivers, who will have to learn the quirks of a genuinely new car.

NASCAR plans to conduct four more test sessions through June, and hopes to have the Next Gen car ready for the 2021 season. Organizers are also considering hybrid powertrains for the 2022 season.