The next generation of NASCAR’s NextGen car will hit the track today at Auto Club Speedway.

Hendrick Motorsports’ William Byron will be driving what NASCAR is calling a “Phase 3 Prototype” over the next two days on the 2-mile oval. The brand new P3 will closely resemble the ballyhooed and dramatically overhauled NextGen car that will make its official debut on NASCAR’s premier circuit next season in what some are calling a “moon shot” for the Cup Series.

The car will replace the Gen 6 in 2021, and its third iteration features many updates based off the feedback garnered from the three tests over the past five months with the P2 Prototype (the original NextGen prototype was tested only in the wind tunnel).

Richard Childress Racing’s Austin Dillon (at Richmond Raceway last October), Team Penske’s Joey Logano (at Phoenix Raceway last December) and Joe Gibbs Racing’s Erik Jones (at Homestead-Miami-Speedway in January) logged a total of 1,011 miles on the P2.

Besides a common chassis, the car also will feature 18-inch aluminum wheels, a sequential gear shifter, rear diffusers and a smaller spoiler.

Here are answers to some pressing questions entering today’s test in Fontana, California:

—What has been updated on the car? Teams and drivers said the P2 was difficult to work on, so NASCAR has made adjustments. The front clip has been opened up to allow easier access to valve covers. Some of the rear compartment structure has been altered for greater efficiency and speed in changing sway bars during a practice session. Installation and removal of shocks, springs and other tuning components also should be swifter. The new car also will offer better visibility for drivers.

–What else is new? With several vendors having been selected that will be the exclusive suppliers for the NextGen car, the P3 will feature some of the parts and pieces from the companies that will play a major role in the 2021 rollout. The car will be as close as possible to what NASCAR intends to race before vendors begin producing in bulk for teams.

–When will teams begin getting the new car? NASCAR still is on track for vendors to begin making parts and pieces so that teams will begin taking delivery on NextGen cars at the end of July. There have been signs that some vendors are beginning to set up shop in North Carolina.

—When is the next test? It will take place after the March 15 race at Atlanta Motor Speedway. As NASCAR cycles through its manufacturers with each test (Chevrolet, Ford, Toyota, Chevy has been the rotation so far), a Ford driver will be behind the wheel. Though the team has yet to be confirmed, Stewart-Haas Racing or Roush Fenway Racing would seem likely candidates after a Team Penske driver (Logano) was at Phoenix.