Fishscaling body panels.
 

Many years ago I owned a Citroen DS sedan.
This car was built on a platform chassis and every body panel was individually adjustable.
The factory advice was to set the panels in a pattern termed "fishscaling" which meant the leading edge of each panel was fitted to sit inboard of the panel ahead of it.
The difference was basically the thickness of the panels (about 1 to 2mm max).

In addition each panel was backed with a rubber strip shaped like a windscreen wiper in section which filled in the gaps between panels.

Citroen took their aerodynamics very seriously so it may be worth the time , for those considering taking aero to the next level , studying the efforts by Citroen and others (Ford Probe aero concept cars comes to mind).

Cheers , Pete.

There were two reasons: One was aero and the second was noise reduction.

The DS was probably the last of the old school French cars built before accountants and government legislators starting telling car builders their jobs.
Sadly they no longer are so individualistic and the practice is no longer followed.

Pete.

Excellent info, Pete! Thank you!

sounds like a good idea. Doubt it'll make a measurable change in mpg but it certainly won't hurt and just might cut some road/wind noise.

I subsequently found out the same technique is often used by sedan car racers on the panel work of their cars.

Every little helps.

Cheers , Pete.