Today we take a look at a small but important area of car body design, the window frames and cant rails.
Up until 1982, the standard solution for mating the roof to the sides of the glass house was a rolled flange. In simple terms, the edge of the roof panel was mated to the edge of the bodyside and welded after being rolled by two folds along its length. The resultant u-shaped structure was rigid and provided a useful gutter to stop water flowing down the sides of the car. In some cases, a chrome sheath was slid over the outer edge of the gutter to protect (or conceal) rust.
The primary disadvantage with the gutter (see the Issigonis Mini) is that it creates turbulence. Conceivably it can be a haphazard operation leading to variability in quality. The solution to this was to make the windows flush and to move the join between the roof and bodyside elsewhere. There seem to be two ways to do this.
The 1982 Audi 100 shows a rather costly and possibly difficult way to do this. The roof panel is welded to the body side along a simple line inboard of the windows. You can see a groove in the image where the welds are. Outboard of that there is a surface that continues the roof´s main forms which leads to a complex steel pressing into which the windows are set and which itself is probably welded to the b- and c-pillars. The a-pillar and d-pillar are thus part of the cant rail pressing. The a-pillar meets the front wing at a simple open panel gap. At the d-pillar a strip of cosmetic plastic conceals the join to the rear wing. The 1986 Omega and W-126 Mercedes did the same (at the pillar to rear wing joint).
In 1983 Volkswagen had a go at the problem. The Golf has a rather large black rubber strip that forms a seal between the roof and the tops of the doors. I have no idea what is going on underneath all that but I imagine it involves a hidden, recessed flange and a lot of welding. The solution didn’t catch on but Skoda re-used it for the 1994 Felicia.
The 1984 Opel Kadett offers a middle ground. It has the cant rail forming a one-piece pressing which includes the a-pillar and d-pillar. In places of Audi’s expensive weld-and-paint solution there is a plastic strip that runs from the top of the front window to the top of the rear screen.
This or a version of this design is in use on most cars today. Depending on the desired level of visual refinement, the plastic strip can be wider or narrower or perhaps body coloured.