1. Rocks crackling beneath the wheels when they turn I think we all know what this sounds like, and it would add tons more immersion. 2. Highway rumble strip I think the strips are in-game, but they make no noise. The devs could just tweak the sound of the racetrack rumble strips. Once the controller vibration gets fully supported, this will be neat to have.
the rumble strips already made noise in hirochi raceway, another thing they could add is like the bumps between lanes on highways, also they should add speed bumps that would be fun with a stanced car