Aerodynamic question

[BCFAST]

Any of you have any hard numbers comparing mileage running with and without your tailgate? It just looks like an uncovered bed would turn a closed tailgate into a parachute.

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97 2500 CC 4x4 3. 54 5spd, Green, #12 plate slid all the way forward, 4inch open exhaust, 235/85 Michelins, RS 9000's, PrimeLoc, Red Tops, TDR cloisonae grill badge!

 

[BHORNER]

Maybe this will settle the Drag argument once and for all.

.
Did You Know?

Improving Aerodynamic Characteristics of a Dodge Ram Pickup Truck.

by Todd J. Ortolani & Vanwijak (Kehm) Ewosakul

Faculty advisor: Dr. Alan K. Karplus

This is a brief collection of information and images from the projects
completed by Todd and Kehm during the Spring semester 1997 in the Department
of Mechanical Engineering. The baseline condition of the pickup was evaluated.
Several conditions including aftermarket devices were simulated in a water
tunnel. A new cap design was developed and tested. The new cap reduces
drag by 30% and provides for a 3 mpg reduction in fuel consumption.  
This project won the 1997 American Society
for Mechanical Engineering Young Design Engineer's Paper Competition
International Award.     

<OL>
[*]Solution to Did You Know?</LI>

[*]Drag Coefficient</LI>

[*]Baseline condition&nbsp;&nbsp;&nbsp;
Cd = 0. 432 (without mirrors)&nbsp;</LI>

[*]Square Cap&nbsp;&nbsp;&nbsp;
Cd = 0. 480&nbsp;&nbsp; 11. 11% Increase in drag</LI>

[*]Replace tailgate with a cargo net &nbsp;&nbsp;
Cd = 0. 461&nbsp;&nbsp; 6. 71 % Increase in drag</LI>

[*]Removed Tailgate&nbsp;&nbsp;&nbsp;
Cd = 0. 447&nbsp;&nbsp; 3. 47% Increase in drag</LI>

[*]Lowered Tailgate &nbsp;&nbsp;&nbsp;
Cd = 0. 414&nbsp;&nbsp;&nbsp;&nbsp; 4. 17% Decrease in drag</LI>

[*]Tonneau Cover &nbsp;&nbsp;&nbsp;
Cd = 0. 381&nbsp; 11. 81% Decrease in drag</LI>

[*]New Cap Design&nbsp; Cd
= 0. 302&nbsp;&nbsp; 30% Decrease in drag</LI>
[/list=a]

At Western New England College, the study of engineering
is about solving real-world problems.

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Barry Horner
Lake Forest
Orange County, Ca

2001, SLT+, ETH, 6 speed, White quad cab, short bed, Sport, 2wd , 3:54 anti spin, Camper Special with trailer tow, 16x8 Forged Aluminum with 265x75 tires, Fog lights, Audio controls steering wheel mounted, AM/FM cassette with CD, Travel Convenience group, Keyless entry with remote, Leather agate heated seats. Line-X bed liner. ARE LS 2 tonneau cover. Pillar mount boost and EGT. EDGE EZ and McLeod clutch.

 

[illflem]

I can't see how a removed tailgate would increase drag while a lowered gate would reduce drag. I've always heard that the least amount of drag was from a stock gate in the up position.

 

[tom sweeney]

dodge rams are designed to actually have a better air flow with the tail-gate in an upright position (normal- closed)... try a search... i know i've seen the topic on this website as well as others... tom

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2001QC 2500HD LB ETH/DEE 4x4 4:10's LSD All options except cab lights,Xcelerator air filter,Forest Green/Light driftwood.

 

[sweeks]

I'm interested (and skeptical) about the claim that a newly designed shell would increase fuel mileage 3 MPG. Is this shell available on the market or was this an experimental / theoretical design ? Any info or pictures would be appreciated. Steve Weeks

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2001 2500 4x4LB,6-speed,HO engine,SLT,towing mirrors,Med. Bronze W/Dark Charcoal Line-x bedliner and rocker panels,CB,Banks EGT/Boost pillar mounted guages,Jacobs E-brake,etc.

 

[Steve Campbell]

I am similarly interested!

 

[RAPID RICK]

Did a mileage test of my own last summer
Ran a 205 mile round trip 3 days a week for
12 weeks. Here are my results:

Tailgate in the up position for two weeks
was a 21. 5 mpg avg. (1279 miles)


Tailgate in the down position for two weeks was a 23. 9 mpg avg. (1254 miles)

Tailgate off for two weeks was a 22. 1 mpg avg. (1267 miles)


This tells me tailgate down is more areodynamic so when ever possible thats the way I run. Rick

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99 3500 4x4 QC,5spd,3. 55 posi,turn over ball goose neck hitch,Putnam class V reciever hitch,Alcoa alum. wheels,275 hp inj. home built boost module,4 in. straight exhaust(built it in my shop)Pac brake,4 leaf overload springs,all options execpt leather & keyless entry,2000 Artic Fox 10 ft. camper,with slide out 2horse tongue pull trlr. ,24 ft flat bed that I haul my 6200# modified alcohol burning Ford 4x4
pull truck on.

 

[RAPID RICK]

Forgot to mention that was with the cruise control set at 62 mph. Rick

 

[Switca]

Originally posted by BHORNERIS:
[*]Square Cap   
Cd = 0. 480   11. 11% Increase in drag</LI>
[*]New Cap Design  Cd
= 0. 302   30% Decrease in drag</LI>

What's a 'square cap'? Are we talking an older cap that's pretty flat and 90 degrees all around?

What's a 'new cap design'? Are we talking new, ARE or Leer cap with not as many 90 degree angles and that 'rounded' look?

If to, I just cut my drag by 30%.

Any ideas about what an x% reduction in drag does to MPG numbers?

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Gregor Switca
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96 2500 4x4 auto SLT.
99. 5 VW Jetta TDI
Nothing but diesel in my driveway.

 

[Bill Lins]

I remember seeing that study about 2 years ago. The "new-style" cap started off @ cab roof height and tapered down to the top of the tailgate, turning the truck into a "fastback" (remember those?). Kind of neat- looking, but not too practical if you use your truck to haul stuff.

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Bill Lins Wharton, TX 98 2500 QC SLT,12 (the CORRECT # of)valves,NV4500,3. 54 LSD,Manik grille guard,Semi-Psychotty Air,Amsoil everywhere, Reading aluminum utility body and bumper,Optima yellow tops- silencer ring & muffler stolen.

 

[Old Account - 243]

I read the study too; remember, they were using a short bed regular cab which will have different cd than all the other Ram configurations. That shell was not really much more than a bed cover with the end near the cab raised to the top of the back window.

I would put a lot more faith in Rick's test than the windtunnel. I'll bet Rick had to work a lot harder too... 3800 miles at 62mph would drive most people insane.

243

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99 QC 2500 ST 4X4 SB 24V/5speed 3. 54/LSD Driftwood/Agate
Walker 21468, VDO, Bridgestone 285/75/16 MT's, RS9000's, Hella 500's

-- email address removed --

 

[jsimpson]

So THAT explains why my fuel mileage numbers aren't so good with my Lance camper in back! It's an aerodynamics thing!!! Gawleee! Shucks, I guess Id better design a slide in camper that is flush with the cab in front and flush with the tailgate in the rear. Hmmmm; where am I going to put my shower??? By the way Bhorneris, thanks for the info. I'll keep my tailgate down now when I'm not hauling; I could use the extra miles on my gallons!

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http://coffeewithJesus. homestead.com/web1.html 89 1-ton, Amsoil System 3000 5-30,K&N air filter, cleaned-up exhaust, Dynomax straight-thru, rebuilt pump, thermostatically controlled twin 14" Permacool electric fans, intercooler), modified 518 OD transmission, Gear vendors OD controler, R-134 refrigernt, louvered front fenders, 93 aftermarket smoothie grille, new Dupont Chromacolor black, black-and-red rubber rubstrip, black headlights, powdercoated bumpers; 78 35'Avion, 93 Lance 900 slide in with generator and power jacks. To see my truck, Click on: <A HREF="http://albums.photopoint.com/j/AlbumIndex?u=1169022&a=10097213

Jesus" TARGET=_blank>http://albums.photopoint.com/j/AlbumIndex?u=1169022&a=10097213

Jesus</A> saves!

[This message has been edited by jsimpson (edited 12-20-2000). ]

 

[jdkenyon]

For anyone that wants to read about it for themselves here is a link to that study.
http://mars. acnet. wnec. edu/~ehaffner/did.htm

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'01 2500 QC SB 4x4 ETH/DEE 3. 54LSD

[This message has been edited by jdkenyon (edited 12-20-2000). ]

 

[Cooker]

jdkenyon,

Thanks for the link. The information provided here was great. I was always hoping to find some proven, tested information like this, and it is even with one of our trucks. Great!

Ryan

 

[DaveN]

Just got back from a short trip to Ohio, I was getting 14 mpg @ 80 mph (according to the computer). Ran like this for about an hour, and then I stopped and dropped the tailgate. I was then getting 16 or 17 mpg. The truck only has 800 miles on it, and I was unloaded. The highway I was on was pretty flat, so the conditions stayed the same throughout the trip.

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2001. 5 2500 4WD Auto QC 3. 54 Loaded except Leather

 

[BCFAST]

Thank you, gentlemen!!! I just knew I could count on you all for my original question... and I hope my querry has helped you all as well! See, this is why we joyfully shell out our $35 every year... 'cause we're the TDR and we help each other out, and those poor saps on the other sites... well, they just bicker. Happy Holdays to All!

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97 2500 CC 4x4 3. 54 5spd, Green, #12 plate slid all the way forward, 4inch open exhaust, 235/85 Michelins, RS 9000's, PrimeLoc, Red Tops, TDR cloisonae grill badge!

 

[Millfly]

Hello guys,
Don't mean to confuse the issue, but a read an article on a study that was done about 4 years ago by Chevy, Ford, and Dodge. They were comparing the ventilated tailgates to the OEM tailgate. Their conclusion was there was no difference in performance between the two. This was an independent study. Go figure.

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2001 Ram 3500 dually, 4:10, auto, SLT+,anti-spin,custom side paint, Custom pin striping,Advanced Thermal Products Sound Blanket Kit, Smittybar nerf step,Geno's stainless wheel well trim, tonneau cover, air dam, chrome monster tip, mud flaps/chrome tips,pyro-trans-boost gauges, Bosch 275 Injectors, Van Aaken, Kondalay TC & Valve Body.

 

[QRTRHRS]

I read of a GM study that implied running with the tail gate down or with a flow through hurt mileage. When flow throughs first hit the market, I made one for a Toyota. My mileage dropped a hair with it.

IMHO, running around with the tailgate down is dangerous. Someone could walk into it same as a hitch sticking out. In an accident, I would think the tailgate would be more apt to fly off. (I know of one case where someone did die this way) One more thing, over time, I would think the bed may loosen up more without the tailgate stabilizing the rear part.

Being my truck has a flatbed, this is a mute point for me anyway. I will shut up now.

 

[Cooker]

I agree on the point that the bed may "losen up. " The tailgate is actually designed to help hold the bed together. I'm almost certain I remember reading this in a post a while back. Also the other drawback to running with the tailgate down is that alot of debris and water will get inside the tailgate because of the "vents" at the bottom. This is especially bad idea in a snow climate where road salt could invade and sit there.

If you still would like to run with the tailgate down. Dump a little drain oil in it to help coat the inside and prevent rust.

Ryan