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Old 09-21-2011, 11:59 AM   #1 (permalink)
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GM has given up on aero fender skirts

GM director of design, Ed Welburn, has conceded that they will definitely not be using rear fender skirts because of many production, cost & marketing drawbacks, even if they do reduce drag & improve fuel economy.
Clearly for the OEM industry, people just don't like them on their designs.

The aftermarket industry and fellow eco-modders can & will fill that 'void'.


Rear fender skirts look great, but flunk in other ways

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Old 09-21-2011, 12:21 PM   #2 (permalink)
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How the Hell do skirts increase tire pressure, increasing the probability of a tire failure?
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Old 09-21-2011, 12:24 PM   #3 (permalink)
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They act like skirts will add half a grand to the MSRP. I doubt it.

If they wanted to narrow the rear a couple inches it really wouldn't make that much of a difference imo. People don't push their cars to the limit anyhow. And cargo space? Please. With the kind of styling shapes they think up for crap it won't matter that much in the long run either. Of course the rear seats will be a little narrower but most seats on 2+2's and small cars are small anyway.

Also, with FWD it would be super easy to narrow the rear track.
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Old 09-21-2011, 12:44 PM   #4 (permalink)
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To be fair, our collective understanding of what happens around the wheels and wheelwells (for some reason Europeans call them wheelhouses, like the Titanic) is just getting started.
For instance, it seems to be a better use of a pair of skirts to put them on the front. (shocking! shocking! It's got to look like an Ecocar!) Airflow at the rear is pretty well settled down, by comparison. (Regert)
Then there's the issue of jetting vortices at the road/tire junction. The front seems to be an area of rapidly changing pressures and velocities, and even a skirt is only a partial solution.
Then there's all the stuff like brake cooling, where the front has to do most of the work, and dissipate most of the heat.
I, for one, would cut them some slack.
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Old 09-21-2011, 01:09 PM   #5 (permalink)
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IMHO the hybrid & EV vehicle niche will still get them. The more 'progressive' designs & shapes, ala the Prius, were to their marketing benefit. It became a design brand icon, that the enlightened buying public was looking for that recognizable aero template. EV1 & the Insight had fender covers that became their 'efficiency' badges. The mainstream consumers may bypass this aero device but FE buyers will recognize and choose these options.
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Old 09-21-2011, 06:26 PM   #6 (permalink)
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"Production and cost drawbacks"? How can they say something like that, do they think their customers are morons?

Why not have them as an option and satisty those who refuse them and those who want them?
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Old 09-21-2011, 06:55 PM   #7 (permalink)
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Quote:
According to Welburn, there are several drawbacks:

• The fender skirt causes tire pressure to increase. Although he did not say it, neither GM nor any automaker wants to create a design that increases the probability of tire failure.

• Removable skirts are difficult to keep in place properly, plus there’s the added cost of each skirt.

• Pick one: To use a fender skirt, the rear tires need to be narrower to fit inside the wheel well or the vehicle track needs to be narrower or the body needs to be what he called “pulled out” to accommodate the same size tires that are steering the car.

Welburn said pulling the body out, essentially widening the body where the rear tires are located, increases aerodynamic drag.

While Welburn didn’t explain the other two choices described above, a narrower tire would reduce vehicle capacity and a narrower vehicle track could slightly increase the probability of rollover.

Says Welburn: "The short answer is, skirts don’t help on a production car."
If you have a heavily loaded tire it will tend to get hot. Pressure increases in a hot tire. If you have an underinflated- you know, like just about everybody drives around on- heavily loaded tire it will get even hotter. Yeah the pressure increase there would be nice but the heat is the worst enemy. If you then partially enclose it you can expect it to heat up more. If you partially enclose it and then use the brakes heavily I'd imagine that wheel well will really heat up. GM HAS to design for the worst case scenario, otherwise idiots and lawyers will sue.

Removeable skirts are fiddly. I think even if you have a robust mounting design, it is in a location often fouled by dirt, mud, and ice.

They'd probably want to paint it body color. Painted parts add cost disproportionatly.

It is undesireable to have front and rear tracks that mismatch by a little- I'd say, by less than 2x the width of the rear tires. This is because on a soft surface (yes people still drive on dirt roads in America) if the rear tires don't fall squarely into the front tires' tracks, they get squirrely. Believe me, it sux.

As always, if someone wants them badly enough, they can make them or the aftermarket can fill that void. (PUN!)

Last but not least, they aren't as great an aero device as we'd like. Mfgs have to scrutinize the pros and cons way more than the likes of us.
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Old 09-21-2011, 08:25 PM   #8 (permalink)
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Quote:
Originally Posted by lowglider View Post
"Production and cost drawbacks"? How can they say something like that, do they think their customers are morons?

Why not have them as an option and satisty those who refuse them and those who want them?
If you design a car to have wheel skirts and leave them off, it looks funny.



If you design a car to have open wheel wells and later add skirts, it looks funny.



(No offense to Sulfuric- I'd post the Probe if the concepts didn't have covered wheels)

So we come to a crossroads: does the company want to go out on a limb and build a car with skirts that people may or may not like? Or do they just build another "safe" car that people are more likely to buy?

I'd like skirts to come back, and to have more EV1's and Insights, but in this economy I don't think companies are ready to take that risk.
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Old 09-21-2011, 08:28 PM   #9 (permalink)
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Quote:
Originally Posted by botsapper View Post
GM director of design, Ed Welburn, has conceded that they will definitely not be using rear fender skirts because of many production, cost & marketing drawbacks, even if they do reduce drag & improve fuel economy.
Clearly for the OEM industry, people just don't like them on their designs.

The aftermarket industry and fellow eco-modders can & will fill that 'void'.


Rear fender skirts look great, but flunk in other ways
This article just goes to show how limited that the field of automotive engineering is in terms of forward intellectual thinking.

I honestly think that skirts WILL be standard on vehicles in the next 10 years. As communities such as ours become more prevalent, the communal knowledge that we convey does as well. It sounds weird, but I believe that consumer comprehension is necessary to see this through. I say this because in order for consumers to demand something, they must first understand it.

It all comes back to the fact that automakers are scared to be TOO innovative for fear of consumer rejection.
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Old 09-21-2011, 11:38 PM   #10 (permalink)
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Quote:
Originally Posted by dieselbeetle View Post
This article just goes to show how limited that the field of automotive engineering is in terms of forward intellectual thinking.
Correction there ... it's automotive styling, not engineering. As in, marketing gurus, focus groups, planned obsolescence, consulting the legal department 137 times over, tailfins...

At first look, that tire pressure comment in the article sounds like total horsepucky. But, what Frank Lee said holds some weight... it boils down to ease of use, saleability, and liability.

Basically the styling boss of GM went the diplomatic route, and didn't say "studies show our customers are stupid and never check their tire pressures until the rim is rolling directly on the sidewall folded over onto the pavement".

Skirts are a cheap scapegoat, but they will also make it harder for people to check the condition of their tires as far as wear, and air pressure goes (even if, in general, people neglect to do that when they're totally exposed in open fenders).

Of course, a spike up to $5/ga gasoline could change opinions markedly...

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