Talk:Automobile drag coefficients

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[edit] Sports cars not terribly aerodynamic

Hi

Although the article _does_ mention that sports cars sometimes tend to sacrifice lower Cd values for negative lift at higher speed, it is misleading to represent normal family cars as having such poor aerodynamic values. Modern sedans, such as many Lexus models, BMWs and Mercedes-Benzs all have Cd values of around 0.26 and 0.27. Additionally, I think a discussion of drag needs to take frontal area into account, as it is the product of these two figures that produces an indicator to the vehicle's true aerodynamic efficiency. Looking at either one in isolation is not particularly useful.

Perhaps the article on the drag equation might be a better place to add this discussion, since that brings in all the contributing factors. However it's still not the full story since without knowing the power of a vehicle's engine it still doen't give you much of an indication of performance. Given enough power, even the most brick-like of vehicles can be made to perform well, at least in terms of speed/acceleration, if not economy. My feeling is that since car frontal areas are more or less of the same order (certainly within a reasonable range, since frontal area derives ultimately from the size of the human body), Cd gives you some relative measure of a car's "draginess", without saying anything about how this affects performance. In fact it's like a lot of figures - they tend to get picked up by marketers and used rather disingenuously, i.e. the try to blind the public with science. Witness the commercials for the 80s model Audi 100, which strongly featured its drag coefficient, as if the average person had a clue what it meant. They even put a decal "Cd 0.3" on the C pillars! So, while I agree with you and think the article could be expanded to include these points, it should also point out the meaninglessness of it, given that it's not a predictor of performance. Graham 00:51, 2 Jun 2004 (UTC)
I was just about to query the absence of frontal area, which is very important to aerodynamic efficiency. A blocky Jaguar XJ40 might not have a great Cd, but it can be efficient as its frontal area is not great. I'm sure mpg figures with more "slippery" rivals such as the Mercedes S-class would bear this out. I'll try to work something in as without it, the discussion of efficiency is incomplete. Stombs 11:56, Jan 28, 2005 (UTC)

[edit] Added some cars

I added the Alfa Romeo BAT, Alfa Romeo Disco Volante, Dodge Charger Daytona/Plymouth Superbird, Hotchkiss Gregiore, Triumph Spitfire, Daihatsu UFE-III, Loremo, Opel Eco Speedster, GM Precept, Dodge Intrepid ESX, 1921 Rumpler, Fiat Turbina, 1933 Dymaxion.

A google search will yield results for most of these, but the Mk I, II, III Spitfires have their Cd quoted in a book titled "Streamlining and Car Aerodynamics" by Jan P. Norbeye.

The Mk IV Spitfire is quoted at the following page:

http://web.archive.org/web/20041118043051/http://www.teknett.com/pwp/drmayf/tbls.htm

The Fiat Turbina is quoted here:

http://www.velocetoday.com/cars/cars_46.php

The Alfa BAT7 is quoted at .19 here:

http://www.velocetoday.com/cars/cars_76.php

Google searches will easily find the rest.


A little rant aside from this topic:

Hard to beleive that such efficient designs could be made back in the 1920s and 1930s. We could have easily used them to double fuel economy during the 70s fuel crisis to around 35-40 mpg without shrinking car size while KEEPING musclecar V8s, but we didn't. Imagine a full size Plymouth Fury-like car, with perhaps a .20 drag coeffiicient. Horsepower required at highway speeds would have been cut by about 1/2, doubling fuel economy.

Less drag = less horsepower required at speed = less maintenance and longer engine life = less money for the Detroit pricks(and Euro tarts, and Japs too, all said tongue in cheek of course. :-)

Today's hybrids are just now catching up to the best cars from 70-80 years ago in drag coefficient, and cutting aero drag is reponsibile for about 70% of their fuel economy improvement over typical gas cars. Slightly reduced weight and a hybrid powertrain along with use of CVT and smaller engine is the rest. This is embarassing. There's no reason we should be driving around in such inefficient bricks today, except that the auto monopolies are very slow to ration out new technology so as to maximize profits on each advancement, even if some of those advancements are over 70 years old, and they want to keep maintenance high and profits up. With the looming oil crisis, I hope they all go belly up, so a bunch of smaller, less centralized companies that are actually responsive to consumer demand like AC Propulsion, Factory Five, Caterham, and Mosler take their place.

Good aerodynamics can also allow 150 mile range pure electric cars without a need for advanced batteries, but again, the auto industry ain't budgin' on that one, considering EVs have one moving part, no oil changes, tune ups, valves, pistons, pulleys, belts, and all that other crap, and with electric motors lasting 500,000+ miles and all! They'd be making less money from us stupid saps on electrics. Think about that, the possibility of 150 miles electric car range with ~1,500 pounds of lead acid golf cart batteries translates to over 750 miles possible with equal weight of today's lithiums, or cut the battery weight in half with today's lithiums, ~300-400 miles in an aerodynamically efficient design! Not enough range?

I also own a 1969 Triumph GT6 MkII converting it to electric, which I've heard had a .32 from multiple racers and enthusiasts, but I nor have any of them never been able to find a verifiable source, so I didn't add it. Also of note is that Triumph never wind tunnel tested their cars, so the .39 and .42 for the Spitfires, while cited from seemingly reputable sources, may have been estimates. But they appear accurate running through an automotive technical analysis(ie. calculate horsepower from the flywheel required at various speeds, usually the top speed, and go from there).


[edit] Duplicate Content in coefficient examples

The example drag coefficients are listed in a long list, then repeated in the image table. I reccommend deleting the list and just keeping the image table. The information is identical, and even if users have images turned off, they will still see the numbers. Also, it seems like there is a lot of examples that aren't providing a lot of value. I reccomend paring down the list, to have a greater difference between examples. We don't need 4 example cars that have .36, four cars at .34 etc. If I dont see objections, I am going to remove the text only list, and reduce the image list as well. Gaijin42 21:03, 1 August 2006 (UTC)

Hi, I made the arduous job of adding the pictures to the numbers. Well, I object to the removal of pictures: Four cars that have 0.36 are of great interest, because you can see that so dispare and distant cars as the Citröen DS and the Ferrari Testarrossa have, in fact, the same Cx. A shorter list could be neater for the less interested person, but the complete list if of great value for the more enthusiastic aficionado. In fact, I would like to have more cars listed here, even cars with the same Cx.
I added the pictures because we had an (amiable) discussion about which shape was aerodynamically better, the sedan or the hatchback...well, the best compromise shape seems to be the Kammback. The rare occurrence of sedans (or saloons, as you wish) in the lowest Cx part of the list would be lost if you start to eliminate "duplicate" Cxs...or maybe a new pattern would emerge adding more cars.
The deletion of information for the sake of "neatness" is not a good thing: The information that is "superfluous" for one reader is "indispensable for another. Please take advantage of the condition of not being printed on paper that Wikipedia has and include all the possible information.Randroide 14:20, 2 August 2006 (UTC)
(NB: See "Gallery" section below for suggested everyone's-happy solution) --tiny plastic Grey Knight ⊖ 13:40, 13 July 2007 (UTC)

[edit] Gallery

Is the large gallery all that encyclopedic? Might it be possible to move it to Commons? --Interiot 18:19, 9 October 2006 (UTC)

I agree. This list of Cd values and gallery is tedious and seemingly endless. While perhaps useful, the list would do better in an article titled, say, ``List of Cd values. I offer this as a suggestion to the maintainers of the list, since I don't want to start rearranging things. Mbelisle 03:48, 22 April 2007 (UTC)
Maybe it all belongs in Automotive aerodynamics where there is already a list? It should be easy to link there so everyone could still find it. Meggar 04:17, 22 April 2007 (UTC)
The article is a bit of a "wall-of-tables" at the minute (as I know only too well, having just restyled them). We should have a selection of values and accompanying images on this page, with the full information on a supplementary page like Mbelisle's suggestion above, I think. --tiny plastic Grey Knight ⊖ 13:40, 13 July 2007 (UTC)

[edit] Convert the picture tables into a real table

Is it possible for someone to transform the picture table into a real Wiki Table? --82.121.249.129 16:34, 13 October 2006 (UTC)

I have added it to my list of Things To Do. :-) --GreyKnight 12:51, 5 January 2007 (UTC)
I did it. --tiny plastic Grey Knight ⊖ 13:40, 13 July 2007 (UTC)

[edit] nomenclature

It would be nice to describe what each variable represents and how it is determined, especially the area "A". —Preceding unsigned comment added by 129.107.97.131 (talk • contribs)

That is explained on the main drag equation page. I don't think we should duplicated it all here, so I have added another link right after the formula. Meggar 01:17, 27 November 2006 (UTC)


[edit] Claimed Cd vs. Actual Cd

It should be noted that the Cd quoted from the manufacturer is not verified in any way - it is a claimed figure. The actual Cd can be significantly higher. I have verified that the Cd from one current production car is 18% higher than the figure quoted by the manufacturer, but unfortunately cannot quote the source. 69.226.56.93 16:37, 25 April 2007 (UTC)

Very interesting point. which model car was this? if anyone can offer more values it would be nice to shed more light on this issue since we know how they can be lying bastards vis a vis who killed the electric car. Dan Frederiksen 11:21, 12 May 2007 (UTC)

[edit] Bus?

It would be interesting to get Cd for some buses. Particularly the flat-fronted tour buses and a comparison between the old truck-like front and new flat front of Blue Bird Corp. school buses. —Ben FrantzDale 18:33, 30 April 2007 (UTC)

[edit] Automotive Examples

Why was the Ford Probe removed from the list that shows vehicles with the least Drag Coefficient? --Settinghawk 23:23, 11 June 2007 (UTC)

[edit] SI Units

Why does this page not use SI Units? —Preceding unsigned comment added by 196.2.99.28 (talk) 17:28, 27 January 2008 (UTC)

[edit] Fair use rationale for Image:Mercedes-Benz Bionic.jpg

Image:Mercedes-Benz Bionic.jpg is being used on this article. I notice the image page specifies that the image is being used under fair use but there is no explanation or rationale as to why its use in this Wikipedia article constitutes fair use. In addition to the boilerplate fair use template, you must also write out on the image description page a specific explanation or rationale for why using this image in each article is consistent with fair use.

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BetacommandBot (talk) 14:07, 8 March 2008 (UTC)

[edit] Chevrolet Corvette Z06 drag coefficients of 0.34 and 0.28??

The Z06's drag coefficient is 0.28 in the table yet in the pictures it is 0.34, why is this? --90.213.246.184 (talk) 17:31, 18 April 2008 (UTC)