super silly post... hoping someone far smarter than myself can shed some light on this dirty-butt phenomena.
Just recently returned from a trip to NE Iowa, which consisted of 5-15 miles a day of wintery dirt roads. I soon noticed how quickly the back of the 4R gets completely covered un dirt/road-grime, esp compared to most other vehicles.
Considering how flat, boxy and vertical the rear hatch is, I can understand how filthy it gets. One only needs to open the rear window at speed to see how there is a "pressure pocket" formed back there which allows stuff to just "swirl" back towards the vehicle....
Now, what I cant figure out is the perfect line of delineation from the lift-gate to the rear quarter panel. How can the D-pillar be nearly spotless? The rear liftgate curves a bit towards the sides, which makes me think it cant just be attributed to surface-angle changes alone. Likewise, the rear bumper seems to "hold onto" road grime on the side of the vehicle far more than the 1/4 panel.
Is this due to the 1/4 panel, liftgate and bumper all being from discrete materials (al, steel, plastic?)