Vellum Venom Vignette: Verbal emissions on greenhouse designs

Longtime reader Kyree Rollerson writes:

Hi Sajeev, I last wrote to you in 2012, and a lot has happened since then. I wanted to pick your brain on three things, all of which are daylight-opening (DLO) related:

What causes DLO fail? You coined that term sometime in the past, but what causes automakers to be unable to make the windshield, front door, and fender meet in a coordinated way?

Or, why would they make a DLO panel that’s partially made from glass and completed in plastic? I saw a current-generation Subaru Forester in traffic and noticed a bunch of tiny details that led up to a massive DLO FAIL. I understand that Subarus have always been more utilitarian than pretty (the BRZ an exception), but this could have been so much cleaner. And, in general, this kind of DLO FAIL didn’t seem to be a thing until the 2000s, so what has caused automakers to suddenly have to resort to it?

Sajeev answers:

The front of the greenhouse (i.e. at the point where the A-pillar meets the cowl) is a tough spot to make pretty these days. As for the root cause, my words from the past might help:

“DLO FAIL is when a design team’s Day Light Opening won’t make production, resulting in replacing glass with plastic cheater panels. Therefore, in internet-speak, the DLO truly FAILS.”

Eliminating the problem you’ve highlighted would likely have cost hundred of thousands of dollars that Subaru clearly could not afford. It started with a “compromised” blueprint and couldn’t turn back once the proverbial wheels were in motion, and Subaru’s Global Platform (SGP) shows this problem via the sistership Subaru Impreza.

Clearly DLO FAIL was baked into the cowl area because of some need for an upright window frame. Making that area sleeker than the window frame necessitated including a fast-looking hunk of plastic at the fender/A-pillar.

Kyree asks: 

What do you think of the return of the four-window greenhouse? I remember sedans and liftbacks in the ’80s having four distinct side windows on ’80s and ’90s cars: a tall, narrow fixed window in the rear door, the two conventional, roll-down windows in the doors, and a quarter window in the C-pillar.

These cars went out of production before 2000, but it started back up a few years ago. There was the 2017 Porsche Panamera, followed by the 2018 Lexus LS, and the 2021 Toyota Mirai. And now we have the new Mercedes-Benz EQE and EQS, and the new fifth-gen Ford Mondeo (for the Chinese market). I have to say, I’m kind of excited to see it. But what say you?

Sajeev answers: 

For me, this combination is less about excitement and more about making a compromised dogleg door design work with a roll-down rear window. Yes, a good design team can make a beautiful fixed window to work around the dogleg, but my (extremely limited) time as a car designer suggests adding fixed windows in doors is highly discouraged … well, at least initially, before the reality of a platform’s hard points sets in.

While it lacks the fixed window in the rear door, the value-oriented Nissan Altima in its fifth generation sports a gen-u-wine quarter window. I guess the dogleg wasn’t restrictive enough to need the fixed window, so maybe designers pushed it into the C-pillar to make the greenhouse look more expensive. Or this could be a function of the door’s internal volume relative to the rest of the body.

Or perhaps the Altima’s rear window doesn’t roll all the way down because Nissan didn’t care to provide that feature to its customers. Whatever, maybe you are on to something and this is cause for celebration!

Kyree asks: 

Wagons that share their rear doors with sedans—your thoughts? The first-generation Saturn S Series was a great example of this. The wagon used the sedan’s rear doors, and Saturn saved some money not having to design or deal with two separate assemblies.

But sharing doors across the sedan and wagon turned out badly for the second-generation S Series. Rather than do something different for the wagon, Saturn just tacked more glass in behind it.

Hideous!

The fifth-generation Honda Accord wagon earned my ire for similar reasons, though not quite as much. So did the Saab 9-5 SportCombi (both the first-gen and the never-realized second-gen). But the one that really broke my heart, because I otherwise loved it, was the Cadillac CTS wagon.

I understand the economics of Cadillac building the wagon at all were so tenuous that it almost didn’t happen, but I do wish the accountants had given GM’s engineers and designers enough money to do the wagon differently.

I do not like the way the wagon’s windows meet on the rear doors with the quarter-panel window. I even made the above graphic to illustrate the difference. What do you think? Am I being a pedant and ignoring a very good car for a stupid thing, or is this a design dealbreaker? Does the production version even look bad in the first place?

Sajeev answers:

I am with you on these concerns, as wagons that share the same window framing as sedans was once an acceptable practice. That’s because sedans used to have upright and functional greenhouses, until CUVs stole their glory. That’s because CUVs are what cars used to be, forcing sedans to be even lower (looking) and sleeker than they were in previous decades. It’s a good thing most wagons died off around this time, because you’ve proven that sleek sedan doors are terrible for the wagon’s mission.

Cadillac clearly cheaped out, relative to something like the E39-chassis 5 Series Touring, a vehicle GM likely benchmarked during the CTS’ infancy. Note just how different the rear window frames are shaped between the sedan and the touring above. It’s clear one was designed for performance, while the other for utility. But the E39 is old news, so let’s check in with something more modern.

Yup, the folks at BMW still spent the money to do it right: Note the size of the quarter windows between sedan and “touring” versions of today’s BMW 3 Series. This isn’t a big ask in terms of time and money, just a new window frame for the rear door to go with all the other changes required to make a sedan into a wagon. Or perhaps it is indeed a big ask, if you aren’t already a dominant player in the European touring car market?

No matter, I have a feeling that LS powertrains and V-series engineering cure all CTS-wagon design ailments for most folks. And this rising tide should lift the value of the V-6-powered CTS wagons, too, eventually. There will be more demand than supply, but these omissions of detail always rub me the wrong way, especially when the competition has a track record of doing that same detail correctly.

Cadillac just never wanted the touring/wagon market as bad as BMW. Probably a good idea, because America is a nation of CUVs and SUVs. But I feel your pain, as endeavors of the most detail-oriented car enthusiasts are precisely what we do here at Vellum Venom. So I thank you for your note.

Do you have a car design question? Email me at pistonslap@hagerty.com and we’ll turn it into a Vellum Venom column! 

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