By on May 26, 2017

BMW Air Curtain, Image: BMW

Mike writes:


I have noticed something on newer cars, and it’s been bothering me for awhile now. Perhaps you, with your deity-like omniscience (and access to inside information) will be able to provide some clarity.

As you can see from the picture below, a new Toyota has this vertical flat area around the wheels. And it’s not just this particular model of car — nearly every modern car I see on the road today has a similar design feature, though they vary in the width of the flat area around the wheel arch. Contrast this the Clinton-era Toyo at the bottom, where the body lines follow a graceful curve all the way to the fender opening.

Old vs. New Camry Fender Flatness, Image: OP

To my eye, the wheel arch flatness looks terrible. Are every automaker’s designers on the same drugs, or is this done for an actual reason — i.e, aerodynamics, or possibly to make the wheels appear larger (another trend which befuddles me)?

Looking forward to your reply, thank you!

Sajeev answers:

Access to inside information in the car design biz? Deity-like omniscience? Hardly. I contacted two experts in aerodynamics and neither responded. Even worse, one is a longtime family friend.

Aesthetically speaking: I agree. The flattened fender arches add an unnecessarily complex or flow-killing stylistic element to a vehicle’s bodyside.

Realistically speaking: The hard transition provides an aero benefit I cannot independently verify. I reckon it reduces drag and/or turbulence around the wheels, especially when adding air curtains. The two might combine to “clean up” (technical term) airflow around the front wheels. Which implies your ride gets quieter and more fuel efficient — not just for fancy BMWs, but also for the Ford F-150 and Mustang.

Which begs the question, how much does this really help? Bullet-nosed faces of the 1990s are history and we still have pedestrian-friendly fronts with extensive amounts of frontal area. Perhaps that’s why air curtains are necessary: every little bit helps.

If you’re a Car Design Wonk, please chime in below or drop me an email.

[Image: BMW, the OP, Ford]

Send your queries to [email protected]com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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39 Comments on “Vellum Venom Vignette: Flattened Fenders and Air Curtains...”

  • avatar

    The Pedestrian Crush Zone has wrecked all kinds of havoc on car design. It is also why doors are so tall correct? They should learn how to make engines flatter!

    • 0 avatar

      Boxer all the things!

    • 0 avatar

      Not really, doors and beltlines started getting taller in the late ’90s thanks to the SUV craze and the Audi TT (which I would say was hugely influential on subsequent generations of car design). Everyone wanted taller cars, even before side-impact crash tests rewarded it. For example, it was a focus group that asked for smaller windows on the PT Cruiser when they were shown a prototype – feeling secure was popular, regardless of how real that security was. A few years later when side-impact tests were happening, VW raised the Mk V GTI’s suspension by half an inch to get a better rating.

      Pedestrian safety standards only started affecting cars in Europe in 2002, and in Japan a few years later, and at the time they weren’t even binding. They resulted in a lot of ridiculous front overhangs and either snub noses or very sloped ones (e.g. Honda Fit). In theory they could have affected beltlines too, if a car had parts of the engine head far back in the engine bay without enough clearance to the hood and the manufacturer wasn’t willing to pay for pop-up hoods. But those cars tended to be expensive (RWD) or US-specific(FWD sedans with V6s) and they were getting tall for those other reasons.

    • 0 avatar

      Wreaked havoc, not wrecked.

      What it’s wrecked is not havoc, but the design itself.


  • avatar

    I enjoy living in a time where my automotive choices are rendered ugly because some low-IQ portion of the population can’t cross properly.

    • 0 avatar

      The EU needs all the support it can get!

      • 0 avatar

        I think he meant pedestrians. But, hey, the people running the EU probably qualify too.

        At any rate – I was once hit by a car, and there’s no such thing as “pedestrian-friendly.” In fact, the term is so stupid that the guy who came up with it should be made a ward of the state. People like that shouldn’t be running around loose.

  • avatar
    Arthur Dailey

    I believe that Nature or the free market would prefer to allow for ‘natural selection’ to occur.

  • avatar

    I have a theory on this. Due to crash regulations the hoods are higher, but the top of the wheel arches remains more or less as it was before. If the designers were to create a transition surface directly from the top of the hood to the wheel arch, it would be too much of a drop in height and wouldn’t look pretty. Adding a two inch lip around the arch affords you to create a transition surface that drops less rapidly and probably looks better.

    • 0 avatar

      I think you’re right, particularly in the rear. That doesn’t sound the way I meant it….

    • 0 avatar
      Secret Hi5

      I like Cactuar’s theory.
      Another possible factor is ever-widening tires?

    • 0 avatar

      The flattened faux wheel arch creates the visual illusion that the wheel well is bigger than it is. Like Cactuar said, this breaks up the transition from the top of the hood to the wheel, but it’s still not enough to disguise the bulk of today’s higher hood heights. Almost all cars have a prominent cut line above the wheel arch to further reduce the visual height.

  • avatar

    This design feature replaces the wheel arches that would be only on the top part of the fender and also believe its easier to manufacture.
    Today’s exotic cars don’t have this feature, Ferrari, Porsche cause it looks cheap.
    Just take a look at a 944 front fender, thing of beauty, the way it flairs wider to the bottom and the rounded softness for the air and water to slide right off.

  • avatar

    As an automotive aerodynamicist, I can comment a little here on the impact of air curtains. We generally see that across various manufacturers, they reduce overall drag by around 5-ish counts. That is, if a car has a Cd of .300, then adding air curtains should get you down to about .295. That really sin’t much of an impact to the total fuel burn of a car, but every little bit helps. 2 counts here, 5 counts there, and before you know it you have gone from 39 mpg to 40 mpg without resorting to under-powered engines or super expensive materials (looking at you, Volkswagen XL1).

    • 0 avatar

      Parenthetical question for you RockBottom – I put weathertech mud flaps on my 2016 F-150, both front and rear. These are rigid flaps…do you think there is much fuel efficiency penalty? The truck is shaped like a brick as it is, so I figure no, but it’s something I’ve always been curious about.

      • 0 avatar

        With wide tires, some states will ticket you if you don’t have mudflaps. So… fuel savings vs. the cost of a ticket.

        On the bright side for those who don’t care about fuel mileage, those flat surfaces are perfect places to add cladding.

      • 0 avatar

        Nah, mud flaps are almost always a drag hit. They do keep your paint nice, though ;)

  • avatar

    I suspect there is some minimal aero benefit, but probably the main reason is just copying of the latest trend. I wonder if it gives some added strength to this part? It does give an easy surface to add some lights or reflectors around the wheel well – another questionable trend.

  • avatar

    The 1966 Olds Toronado had flared fenders with flat faces. Very handsome car. I think it still influences the industry.

    • 0 avatar

      You beat me to it, macnab. And of course the ’66 Toronado had Cord-inspired details (the wheels, e.g.). Plus ça change, plus c’est la même chose.

      Obligatory clip:

  • avatar

    I will take this over the current Silverado wheel arches any day.

  • avatar

    Well, the new Challenger Demon doesn’t flatten at the outside edges!

    I doubt the flat gives any strength. Curves and angles give metal resistance to bending and warping. Look at the old F-150 and the crease down the side. That was put there to give it more resistance to bending.

    I imagine it is easier to put the new side markers on and it could also be a styling trend. Just like the gaping maw that Audi started many years ago.

    I may also help with aero since it isn’t “flipping” the air out around the tires but allows a smooth transition. Look at all the widebody SCCA/Trans Am cars, they bring the fenders out early and transition flat along the opening. Also the 944 as mentioned above and the e30 M3 if you look at street cars widened for wider tires.

  • avatar

    Is this the production car equivalent of the bargeboards you saw on F1 cars? They did reduce drag in that app,cation although these are obviously far less extreme applications. You do also see the same element on high end hyper cars like the LaFerrari and McLaren P1.

  • avatar

    I asked one of the exterior designers in our studio about the flattened fender arches a few weeks ago, and his response was that they are necessary because today’s cars are all ‘overbodied,’ that is, without the flat spot they would overhang the wheels too much. Looking at the Corollas in the example pics, you can see the current one is much more bulked up. I prefer the look without the flattened arches, but he was pretty definitive in his answer, and is not the type of designer who blindly follows trends.

    • 0 avatar

      ???? What do you mean by overhang the wheels too much?

      • 0 avatar

        Look at the picture at the top of this article. If you did not cut the fenders off with the flat surfaces, they would continue outward another few inches until they reach the intersection with the wheel openings. This would result in the appearance of the fenders sticking out way beyond the wheels (or overhang, like a Nash Metropolitan when viewed from the front.) So they use the flattened arches to truncate the arch of the fenders at the outside face of the wheels themselves, away from the wheel openings.

        Along with DLO failure and flame surfacing; it is a compromise in styling brought on by aerodynamics and safety standards; some surfaces have to be in some places, so they add these features to “clean up” the design. The bit about the “air curtains” probably also plays a role.

    • 0 avatar

      Sounds about right. You wouldn’t want the vehicle to look *too* chubby or bulky, even if it is, you can therefore mitigate this somewhat by shaving unnecessary “fat” off. Reduces the muffin-top look, I bet.

      If we were shown some examples without the necessary trimming, we’d probably agree its better the way we have it.

  • avatar
    Corey Lewis

    I think Nissan did this first. Back in 02 the 350Z had flat wheel arches.

    • 0 avatar

      I have an 03 Z and this is one of the lines on the car I HATE. Overall the car has very smooth, organic flowing shapes, then you reach the wheel arches and it falls flat off a cliff! Its almost like the wheel arches should have be continued to be curved but that made them stick out 2″ too wide so they just sliced them off. Some after market bits to fix this are available, but they look tacked on and thus even worse to me:

    • 0 avatar

      And before that, the 1995 Maxima had them.

  • avatar

    This decade has the ugliest cars in my lifetime. And I go back to the early Eisenhower Administration.

    • 0 avatar

      Agreed. And I go back to the early Carter Administration. The Pontiac Aztek looks good compared to some of the chaff rolling off the assembly lines these days.

      • 0 avatar

        I wonder how much of it is lowest manufacturing cost, hamstringing designers? Take the bumpers off a 1965 Impala and compare to a bumperless 2015 Impala. There’s only so much a designer can do when the manufacturing process dictates so much of the shape.

  • avatar

    Thank you for posting my question, Sajeev. Interesting reading the replies so far- as I said, I suspected aero was the main driving reason behind the “fender flatness”, though the stylistic explanations make sense, too.

    You can look at cars models from approximately M.Y. 2000 on and see the size of the flatness growing, starting from maybe an inch or so in width up to 2 or 3 inches on the newest models.

    I still notice this trend on most of the newer vehicles on the road, and it extends even into full sized trucks and SUVs. And it still looks hideous, to my eye.

  • avatar

    Aero. Note also a flat body section on many cars between the rear wheel and the bumper. Corolla it is very noticeable, and Prii have it too.

  • avatar
    V-Strom rider

    My M235i has them – my least favourite part of an otherwise beautiful car.

  • avatar

    Truly hate those flat arches, one reason I love my 2000 Lexus GS, it has box-flares! real, live box-flares! Todays cars are nearly indistinguishable from one another and the interiors even more so. The designers today strike me as being more interested in anime and comic books than in cars, hence cars and trucks becoming so cartoonish. I drove a Lexus NX loaner a few weeks ago and was embarrassed to seen in the thing, and not even because of the grille, but because of the giant flat wheel arches.

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