I noticed that Heat haze effect works also when vehicle are moving.
Heat Haze effect should be displayed only when vehicle are standing with engine on, because with speed the effect is not visible in real life, this should also give back some fps with a lot of vehicles, and also improve the visual effect, because heat air effect in the tail (big notice on Megane) looks like bad aliasing with the rear wing shadow.
I suppose that you know that also rain can fall inside the tunnel
and dirt grass and small sand stones(when you hit outside of the track), are visible on the bottom of the cockpit
I suppose you know this because its the same on rF1