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Old 01-30-2019, 12:45 PM   #11 (permalink)
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Quote:
Originally Posted by Vman455 View Post
To get back to the original question: it is impossible to say just by looking what the difference in the drag coefficient of two trucks is.
I agree, but based on known archetypes and our own memories we can make a good guess.

I really don't think that is the most fruitful topic here though.

The forum is filled with the results of deleting wheel flares and plugging up fog lights and unnecessary air inlets on front aprons.

Heck we pretty much know what to expect from side view mirror deletion don't we? I added a passenger side view mirror on my 1977 car because I wanted to be able to back up and park better and also lower my risk of wheel rash.

Seems to me by reversing such results we can quantify their reinclusion.

In the original example the mock fog-light openings / brake cooling ducts will increase the drag but more importantly affect stability in cross winds on the highway. They are added to the design to communicate enhanced performance, but nothing could be father from the truth unless they are blocked off behind the opening.

I have asked for better pictures but none have been forthcoming so I have to assume indifference or ignorance by the original poster.

I would look up these details myself but the year and model package of each vehicle has not been posted so I do not specifically know what to look for.

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Old 01-30-2019, 12:49 PM   #12 (permalink)
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Quote:
Originally Posted by Hersbird View Post
..............Also as demonstrated in the 2019 version EPA ratings, the makers get to use their best numbers available in the test even on the worst packages. Case in point the Rebel with higher ride height, big mud tires, and less air dam gets no penality in its EPA rating. Real world it's a good 3 mpg hit.
I did not know this, do you have an article/link explaining the rational behind it?
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Old 01-30-2019, 01:14 PM   #13 (permalink)
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Vman, but take that last pictured example. They say class leading cd of .36 (or whatever) but that may not be the 4x4 Long Horn on 20" wheels pictured, but maybe a 2wd HFE model with the grill shutters, lower ride height, smaller mirrors, and 17" narrower, shorter tires.
Journalists will often just use stock images they like, not specific trucks they tested, if they even did a test at all.
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Old 01-30-2019, 01:20 PM   #14 (permalink)
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Quote:
Originally Posted by freebeard View Post
I don't see the difference. What year Silverado is that? My son bought a 2018, but the big advance is on the 2019 models:


gmauthority.com:2019 Silverado And Its Aero-Enhancing Air Curtains: Feature Spotlight
The SS was from 2003 to 2006 I think. The problem with the new truck is they may have reduced the Cd but they increased the frontal area for an overall increase in overall drag. At least the economy numbers went down on the drivetrains that didnt change 2018 to 2019 while the 2019 lost weight as well.
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Old 01-30-2019, 01:35 PM   #15 (permalink)
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Quote:
Originally Posted by kach22i View Post
I did not know this, do you have an article/link explaining the rational behind it?
TFLtruck does YouTube comparisons and they bought a long term 2019 rebel test truck. Then it did the worst compared to its EPA rating during testing compared to the Ford and Chevy. Viewers pointed out the Rebel test truck although bigger tires, higher ride height, different gearing, had the exact same EPA rating as a basic truck (no off road package) with the same 5.7 Etorque motor. So obviously the EPA doesnt seem to care about gearing, tire packages, cab size, etc. FCA gets to only do 6 tests, one V6, one 5.7, one 5.7 with Etorque one 2wd one 4wd of each of those. They might really have 30+ possible combos that will certainly effect MPG but they get to use the best possible.

The first place I noticed this was the Ford Flex vs its Lincoln counterpart. Obviously very different bodies with the same powertain and platform. Ford got to use the same numbers for both cars so they don't have to compete with themselves basicslly. You can't tell me these two cars have the exact same drag but Ford does.
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Old 01-30-2019, 02:43 PM   #16 (permalink)
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Quote:
Originally Posted by Hersbird View Post
You can't tell me these two cars have the exact same drag but Ford does.
They might! Once more for the folks in back, we can't tell by looking. If we could, then you would know that this car:



...has a higher drag coefficient than this car:



...just by looking at them. Only you wouldn't unless you looked it up, because you would think that the extra scoops for cooling and the huge wing out back would significantly increase the Cd of the Porsche compared to the Viper. But it doesn't--the Porsche's Cd is 14 counts lower.

(Also, the picture of the 2019 Ram I posted is a 4x2, surprisingly. Did you know that the 4x2 has had more ground clearance than the 4x4 for several years now?).
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Old 01-30-2019, 03:22 PM   #17 (permalink)
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squarish/roundish

Quote:
Originally Posted by Taylor95 View Post
I am more interested in the aerodynamics of the body than the tires. But it doesn't really matter. I was also wondering what those holes in the front of the SS were for. Does anyone else think that the more squarish shape of the SS has a detrimental effect on aerodynamics? I would think that the more rounded shape of the other versions of the Silverado would aid FE better.
The big dogs say that there's no magic radius for the forebody.Once you have enough leading edge radius to achieve attached flow,there's little else to be gained with more softening.
The challenge is separated flow in the aft-body,and it's attendant pressure drag.
According to Wolf Hucho,the entire premise for streamlining is addressing this pressure drag of the aft-body.
The squarish 1st-gen,Cd 0.475, Chevy S-10/GMC Sonoma was reduced to Cd 0.315 by Gale Banks Racing.
GM's roundish Holden Ute was Cd 0.309 with it's factory tonneau cover.
The Cd 0.44 Toyota T-100 streamlining netted perhaps Cd 0.218,considering the DARKO/A2 wind tunnel discrepancy.
*cooling drag on trucks is high.Cd 0.027 on the T-100
*side mirrors on T-100 were Cd 0.023 between out and folded.
*the cab/bed gap measured Cd 0.016 on the T-100
*a belly pan with 2.8-degree diffuser could net -Cd 0.07
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Old 01-30-2019, 09:22 PM   #18 (permalink)
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This discussion is pretty interesting. To answer an earlier question, both of the trucks in the op are 2003. I was kind of disappointed not to find the Cd of either truck posted anywhere. It would be nice if an agency mandated that this information should be posted. It would definitely aid consumers like us.
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Old 01-31-2019, 09:24 AM   #19 (permalink)
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Quote:
Originally Posted by Taylor95 View Post
This discussion is pretty interesting. To answer an earlier question, both of the trucks in the op are 2003.
That information should be up front and not left to guess work Taylor95, you waste people's time otherwise.

None of the SS lower openings appear to be blocked off.

SS
https://www.performancetrucks.net/fo...-cover-523594/


SS
2003 Arrival Blue Silverado SS for sale - SSs & VHOs Only - SilveradoSS.com


Stock Silverado 2003-2005 front
https://www.motortrend.com/cars/chev...ilverado/2005/


Silverado



Picture of 2003 Chevrolet Silverado 1500 LS RWD
https://www.cargurus.com/Cars/2003-C...tureId=4042453


Tow hook openings and fog light openings all appear to be closed off on the standard Silverado.

The bottom picture shows a fog light delete option, and that too is blocked off.

CONCLUSION:
Eliminating ride height and tire differences, the SS (Super Sport) lets more untamed and turbulent air underneath the vehicle.

Therefore handling on the highway especially in crosswinds will be inferior on the SS and most likely the SS will have slightly higher drag coefficient.

Remember, the front of the vehicle (lower apron) while moving underway though the air is the highest air pressure zone, lots of air can potentially be pushed through those small openings.

Study case example below, my own pickup truck.

Pickup Truck Aerodynamics - CFD Study Chevy S10
https://ecomodder.com/forum/showthre...s10-35043.html
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1989 Scat II HP Hovercraft

Chin Spoiler:
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Rear Spoiler Pick Up Truck
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Roof Wing
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Old 01-31-2019, 09:48 AM   #20 (permalink)
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Quote:
Originally Posted by Vman455 View Post
(Also, the picture of the 2019 Ram I posted is a 4x2, surprisingly. Did you know that the 4x2 has had more ground clearance than the 4x4 for several years now?).
Hilarious, no I did not know this.

Do you know why the pickup truck manufactures about 10-15 years ago went to huge wheel well openings?

Another feature of pickup trucks that has evolved is huge grill openings, it was once described in this forum as a result of some kind of Diesel cooling requirement increase.

Your sport car examples are excellent.

It still blows my mind that so many of the sleek mid-engine prototype concept cars from the late 1960's through the mind 1970's had such terrible Cd's. For the most part it seemed to stem from the belly pan or lack of, and the engine bay left open at the underside. I posted a few images, some were based on plastic models by Revell and the like.

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1989 Scat II HP Hovercraft

Chin Spoiler:
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Rear Spoiler Pick Up Truck
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Roof Wing
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