Both series have a problem with the cars being ridiculously aero dependent. The cars work great in open air, but as soon as they get behind someone, the handling turns to trash. If they want to get back to racing like it was in the 90s, then they need to shed as much downforce and aero dependency as possible. F1 should consider running a single element front wing, narrowing the front wing, or maybe even no front wing. NASCAR needs to get rid of the splitter, return to the air dam, and require a minimum height so that the cars aren't vacuumed down to the asphalt. There's a reason they used to be able to run side by side and nose to tail at tracks like Charlotte, and they can't do it anymore.