Theme: Evolution – Cant Rails and Window Gutters

Today we take a look at a small but important area of car body design, the window frames and cant rails. 

2015 Land Rover Defender. Possibly the last passenger car with guttered side-glass: Topgear.com
2015 Land Rover Defender. Possibly the last passenger car with guttered side-glass: Topgear.com

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.

1982 Audi 100 with its famous flush side glass: wikipedia.org.
1982 Audi 100 with its famous flush side glass: wikipedia.org.
1986 Opel Omega cant rail. Notice there is no visible weld on the roof. The a-pillar and c-d pillar and roof are one pressing. Wikipedia.org
1986 Opel Omega cant rail. Notice there is no visible weld on the roof. The a-pillar and c-d pillar and roof are one pressing. Wikipedia.org

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).

1983 VW Golf cantrail
1983 VW Golf cantrail

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.

1984 Opel Kadett cant rail which set the standard: conceptcarz.com
1984 Opel Kadett cant rail which set the standard: conceptcarz.com

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.

1994 Skoda Felicia: wikipedia.org
1994 Skoda Felicia: wikipedia.org

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.

Author: richard herriott

I like anchovies. I dislike post-war town planning.

23 thoughts on “Theme: Evolution – Cant Rails and Window Gutters”

  1. I had a look in the urban dictionary which is not the most reliable of sources. That was the first I had heard of that usage for the word “flange”. I was only knew the word from yoghurt pots and engineering.

  2. Opel / Vauxhall have always paid particular attention to the glasshouse and roof sections. Both the Omega A and B1 had well implemented flush treatments, as have various Astras. Indeed, the current Astra reverted to flush glazing after the pressed panel hiatus of the previous model.

    The strangest treatment I have spotted is the BMW 3 Series. Since the E46 BMW have used a huge cant rail / three quarter panel pressing, disguised at the roof with a thin plastic strip. Matched to this is an odd flush glazing scheme whereby the top edges of the window frames feature what I can only describe as a “rubber flap”. You can see it clearly in the linked image below.

    Examining a five year old 3 Series in a car supermarket, I spotted this treatment after observing that the top edge of the window had curled and discoloured at a different rate to the other black trim pieces. I cannot remember seeing this arrangement employed by any other marques, or indeed seeing any prominent rubber trim on any consumer product since a mid 1990’s Electrolux hoover. I am sure other commenters will enlighten me, however.

  3. That´s pretty messy, isn´t it? I think rubber bits ought to be hidden away as much as possible. That protects them from sun damage for a start. I would use a rubber seal as a way to fill a variable gap on a complex closure. I think windows and doors are famously problematic details. The BMW solution means there is no gap between the door and the body at the expense of reduced longevity.

  4. I had a look at some cars. There are three ways to place the door-body split. One is to have the visible cant rail as part of the doors. When the door opens, the cant rail moves with it. The other is to have the door frame recessed. That design is the one where you see a rubber seal most evident. The third solution is to have the split running halfway along the cant rail´s length. I notice the Opel Corsa has a complex solution where there is no rubber visible. A metal body coloured fame closes into a recess in the cant rail. It leaves a 3-5 mm gap but seems durable to me.

  5. I remember a rather interesting solution on the Citroën Xantia. It apparently has been used also on other cars in the ’90s. The door frames are wrapped over the the weld and meet the roof on the top. They also touch the windscreen (not litteraly, but there is no other part visible in between). There is no (visible) trim necessary, but I remember that the door edge started to protrude a little over the roof level when my Xantia got older.

    Can this be considered a variation of a solution that was already mentioned or is it something completely different?

  6. I the mid 70s, I visited Ford’s Dagenham plant where they were building the Mark 3 Cortina. There I watched them lead loading and grinding the weld join of roof to C pillar in order to get a continuous flow all the wheelarch. Even then it seemed an antiquated process that had more to do with coachbuilding than mass production. And the end result was of dubious worth. Spot the join!

    1. From memory the join was here. I don’t mean it’s bad for any other reason than economy. Coming from the company who pissed on BMC’s chips, discovering how much money they were losing on the Mini, after their success with their moneyspinner Cortina 1, it’s amazing that Ford would do something so labour intensive (and skilled labour at that) on the Mark 3. They welded the roof to the top of the C pillar, filled the seam with lead, then ground it down to be invisible. And they did it all very well. But it was an archaic pre-War process to use on a mass production car, even then. The Fiat Strada/Ritmo (“hand-built by robots”) came out only 3 years after I witnessed it. Ford weren’t the only ones, of course.

  7. Made my old job much harder when gutters disappeared.
    With gutters you could put a car up on the peak of an old car transporter body and reasonably safely pigeon step your way back alongside to safe decking by digging your fingers into the gutter.
    No gutters made it much more dicey up there…some of those old transporter bodies used to narrow right down to the standard track of a normal car, so when you reversed all the way up and dropped the back wheels in the cut outs, you’d get out of the car some 15ft up and the deck would be the same width as the car where you were standing, try that with no gutter to hold onto and levitation only available to the Uri Geller’s of the worlds.

    Designers, what are they on, apart from the Japanese traditionalists of the breed they never give a moments thought to the poor mechanic who’s going to have to service and repair their latest whimsy, neither do they consider the poor transporter driver, bah!

    1. I doubt they had falling truck drivers in mind. I can’t say I miss gutters but they were a natural place to hang brightwork. Which I like. The newer solutions are impressive in their elaboration even if you don’t like the appearance. The cant rail seems to be made of one more folded sheet, welded and curved (not in that order). One section could have four or six folds and also neeed odd hollows for bolts or door mating. All that needs to trace a sweep along a long arc of variable radius to an accuracy of 0.25mm or less (someone correct me). Cars are incredible, even the really boring ones.

  8. Economy for its own sake is as silly as wasting money. Presumably Ford had costed this and found it affordable. It’s rather charming to see. I wouldn’t have spotted it. It makes me like the car more. The Ritmo screamed expediency though on paper it looked smart. All those flat planes and straight lines were there to suit the machines. This small contast supports my view that 80s angularity was a response to process changes.

    1. Were Myles Gorfe here, he’d point out that the same elegant solution was used on the first Granada, which is no more than you’d expect from the World’s number one car maker. In truth it was a common solution. Vauxhall did the same, if you look at a Victor FD or FE. So did cars as different as large Mercedes and Hillman Hunters, but the crease at the bottom of the pillar made it less obvious.

      Ford will have costed it, but at the start of a decade that saw huge inflation and unions militant for their own members financial interests, so did they cost it correctly? Certainly, by the mid 70s, Cortina 4 and Granada 2 had a vent panel hiding most of the join. Through flow ventilation gave designers the chance to avoid an obvious piece of trim.

  9. It seems very passive aggressive to me. I think we can do without this in-fighting here. Does your “mate” have issues with Myles or something? And which big Vauxhall are we talking about here? A Sintra?

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