Go Back   EcoModder Forum > EcoModding > Aerodynamics
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 06-02-2013, 07:25 PM   #1 (permalink)
EcoModding Lurker
 
Join Date: Apr 2013
Location: United States
Posts: 34

The Dakota - '99 Dodge Dakota R/T
90 day: 16.4 mpg (US)

The Honda - '88 Honda CRX DX
90 day: 47.43 mpg (US)
Thanks: 0
Thanked 5 Times in 5 Posts
Removing Tailgate

First, I just want to say I already know this has been discussed to death here. Now, moving on.

I've always driven the Dakota with the tailgate installed and up. All indications showed that at highway speeds, that was the way to go. I knew that every vehicle reacts differently to it, but I'd never seen anyone show a statistically significant increase.

Then, a week ago I was on my way home (night time and raining) and noticed a gorgeous red first-gen Insight sitting in what looked like a dealership lot. I turned around to check it out. Turns out it wasn't for sale, and had a CVT anyway. I go to back out the way I came in, in neutral letting the Dakota roll back at sub-walking pace. Then it stops mysteriously. Whet the hell? I couldn't see anything out the back, I hadn't hit any of the other cars... I got out and discovered that a light pole (with lights off) had located itself INSIDE my rear bumper and folded my tailgate like a banana! It was about 2" around and almost entirely solid. If someone hit it at 15 it'd cut the car in half. Obviously, I was pissed.

A few nights later I decided to take the tailgate off, because it was so hideous. I also took the opportunity to remove my pair of 50lb sand bags, which hadn't noticeably affected mileage when I added them, and allowed the Dakota to drive at normal speeds without doing big burnouts and snap oversteer (only small burnouts and controlled oversteer). Now that it's June, they're not necessary anymore unless I want to drag race on the street, which I don't. I've been driving it like this for about a week now. Now, normally I get to half-tank at about 150-160mi in normal commuting. I was expecting about the same now, but I just crossed half-tank at 195mi. I've never seen that before. Now, the weather is getting better here lately, although still happens, so that's going to improve things as well. But, I've also got a tire that's leaking pressure and is almost always low.

We'll see how the full tank comes out, but so far I'm very surprised at what I'm seeing.

  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 06-03-2013, 07:31 AM   #2 (permalink)
Recreation Engineer
 
KamperBob's Avatar
 
Join Date: Dec 2009
Location: Somewhere USA
Posts: 525

Black Stallion - '02 Toyota Tundra 4WD xCab

Half Pint - '06 Yamaha XT225
Thanks: 333
Thanked 138 Times in 103 Posts
Possibilities

Yes a full tank (ideally more) would be more statistically sound. Meanwhile, a couple thoughts. Less weight could improve FE city. Different gas. Others?

Quote:
Originally Posted by JETZcorp View Post
First, I just want to say I already know this has been discussed to death here. Now, moving on.

I've always driven the Dakota with the tailgate installed and up. All indications showed that at highway speeds, that was the way to go. I knew that every vehicle reacts differently to it, but I'd never seen anyone show a statistically significant increase.

Then, a week ago I was on my way home (night time and raining) and noticed a gorgeous red first-gen Insight sitting in what looked like a dealership lot. I turned around to check it out. Turns out it wasn't for sale, and had a CVT anyway. I go to back out the way I came in, in neutral letting the Dakota roll back at sub-walking pace. Then it stops mysteriously. Whet the hell? I couldn't see anything out the back, I hadn't hit any of the other cars... I got out and discovered that a light pole (with lights off) had located itself INSIDE my rear bumper and folded my tailgate like a banana! It was about 2" around and almost entirely solid. If someone hit it at 15 it'd cut the car in half. Obviously, I was pissed.

A few nights later I decided to take the tailgate off, because it was so hideous. I also took the opportunity to remove my pair of 50lb sand bags, which hadn't noticeably affected mileage when I added them, and allowed the Dakota to drive at normal speeds without doing big burnouts and snap oversteer (only small burnouts and controlled oversteer). Now that it's June, they're not necessary anymore unless I want to drag race on the street, which I don't. I've been driving it like this for about a week now. Now, normally I get to half-tank at about 150-160mi in normal commuting. I was expecting about the same now, but I just crossed half-tank at 195mi. I've never seen that before. Now, the weather is getting better here lately, although still happens, so that's going to improve things as well. But, I've also got a tire that's leaking pressure and is almost always low.

We'll see how the full tank comes out, but so far I'm very surprised at what I'm seeing.
__________________
Recreation Engineer
  Reply With Quote
Old 06-03-2013, 02:32 PM   #3 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 27,562
Thanks: 7,738
Thanked 8,554 Times in 7,041 Posts
Just go easy on the brakes. An unladen pickup truck can lose the rear wheels in a panic stop, through loss of traction. Or at least one '54 International would.
  Reply With Quote
Old 06-03-2013, 04:22 PM   #4 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,513

Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 52.71 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 70.75 mpg (US)

Appliance car - '14 Mitsubishi Mirage ES (base)
90 day: 60.16 mpg (US)
Thanks: 4,058
Thanked 6,957 Times in 3,602 Posts
Cannot... resist... urge... to ... post... link:

http://ecomodder.com/forum/showthrea...ery-11445.html
__________________
Project MPGiata! Mods for getting 50+ MPG from a 1990 Miata
Honda mods: Ecomodding my $800 Honda Fit 5-speed beater
Mitsu mods: 70 MPG in my ecomodded, dirt cheap, 3-cylinder Mirage.
Ecodriving test: Manual vs. automatic transmission MPG showdown



EcoModder
has launched a forum for the efficient new Mitsubishi Mirage
www.MetroMPG.com - fuel efficiency info for Geo Metro owners
www.ForkenSwift.com - electric car conversion on a beer budget
  Reply With Quote
The Following 3 Users Say Thank You to MetroMPG For This Useful Post:
aerohead (06-08-2013), Cd (07-09-2013), UltArc (06-03-2013)
Old 06-03-2013, 04:51 PM   #5 (permalink)
MPGuino Supporter
 
t vago's Avatar
 
Join Date: Oct 2010
Location: Hungary
Posts: 1,807

iNXS - '10 Opel Zafira 111 Anniversary

Suzi - '02 Suzuki Swift GL
Thanks: 828
Thanked 708 Times in 456 Posts
Quote:
Originally Posted by MetroMPG View Post
Cannot... resist... urge... to ... post... link:
Resistance is futile.
  Reply With Quote
Old 06-04-2013, 02:46 AM   #6 (permalink)
EcoModding Lurker
 
Join Date: Apr 2013
Location: United States
Posts: 34

The Dakota - '99 Dodge Dakota R/T
90 day: 16.4 mpg (US)

The Honda - '88 Honda CRX DX
90 day: 47.43 mpg (US)
Thanks: 0
Thanked 5 Times in 5 Posts
I know that what I'm seeing here is no very scientific, but given that my commute is 90% highway at least, and therefore more biased toward aero than weight, that leads me to believe that the noticeable improvement in range (and coast-down) is due to the aero, the weather, or likely a combination of both. I don't see weather adding this much on its own; it certainly didn't last summer.

But, obviously the Ecomodder community is very difficult to sway, and that's great! So I tell you what, when I get another tailgate (gotta have one for ice chests, chainsaws, etc) I'll do some actual ABA testing. If the ~2mpg gain that the gauge seems to be predicting is related to the tailgate, it should be pretty obvious in an ABA, considering how many percent that comes out to.

As for safety, my rear brakes would struggle to stop a tricycle, so I don't see the rears locking. And if they try, I have ABS back there, which has never been called on. The fronts, which don't have ABS, most decidedly have locked up before. Big smoke, very scary.
  Reply With Quote
Old 06-04-2013, 09:39 AM   #7 (permalink)
Batman Junior
 
MetroMPG's Avatar
 
Join Date: Nov 2007
Location: 1000 Islands, Ontario, Canada
Posts: 22,513

Blackfly - '98 Geo Metro
Team Metro
Last 3: 70.09 mpg (US)

MPGiata - '90 Mazda Miata
90 day: 52.71 mpg (US)

Even Fancier Metro - '14 Mitsubishi Mirage top spec
90 day: 70.75 mpg (US)

Appliance car - '14 Mitsubishi Mirage ES (base)
90 day: 60.16 mpg (US)
Thanks: 4,058
Thanked 6,957 Times in 3,602 Posts
ideal attitude - thanks!

Quote:
Originally Posted by JETZcorp View Post
But, obviously the Ecomodder community is very difficult to sway, and that's great!
Merci, monsieur, for posting that. Best thing I've read so far today.

By the way, when I posted that thread link, I wasn't implying that it's outside of the realm of possibility that for your particular truck/cab/bed combination, a missing tailgate might benefit. I'm not up on the exceptions to the rule of the tailgate up being better for aero.

I'd just hate to see someone draw a conclusion about a mod and decide it's "good" when the effect might have been the result of some other uncontrolled factor.
__________________
Project MPGiata! Mods for getting 50+ MPG from a 1990 Miata
Honda mods: Ecomodding my $800 Honda Fit 5-speed beater
Mitsu mods: 70 MPG in my ecomodded, dirt cheap, 3-cylinder Mirage.
Ecodriving test: Manual vs. automatic transmission MPG showdown



EcoModder
has launched a forum for the efficient new Mitsubishi Mirage
www.MetroMPG.com - fuel efficiency info for Geo Metro owners
www.ForkenSwift.com - electric car conversion on a beer budget
  Reply With Quote
Old 06-04-2013, 01:24 PM   #8 (permalink)
MPGuino Supporter
 
t vago's Avatar
 
Join Date: Oct 2010
Location: Hungary
Posts: 1,807

iNXS - '10 Opel Zafira 111 Anniversary

Suzi - '02 Suzuki Swift GL
Thanks: 828
Thanked 708 Times in 456 Posts
Quote:
Originally Posted by MetroMPG View Post
I'd just hate to see someone draw a conclusion about a mod and decide it's "good" when the effect might have been the result of some other uncontrolled factor.
And that's the exact point, right there. Eco-tuning a gasoline-powered vehicle is tricky, to say the least. I've seen in my experimentation things that just don't make sense - for instance, highway commutes with A/C using the same amount of fuel as without A/C (the Karen-mobile), or slightly less (the Fiat Dakota).

I'm pretty convinced it has a lot to do with the fact, that gasoline engines in general have to use fuel solely for the purpose of creating and maintaining intake manifold vacuum. This is why, for instance, it's possible to get awful gas mileage while driving steadily at either 25 MPH or 75 MPH. It's possible to make a vehicle more aerodynamic, for instance, only to see the expected fuel savings go away because the engine now has less of a load to push forward -> intake manifold vacuum goes up in order to compensate for the lesser amount of demand -> engine now has to work at maintaining this higher vacuum -> total fuel burned paradoxically goes up.

The converse is true, and I've seen this, too. Load a vehicle with more weight (like I did with the Fiat Dakota) -> engine loading goes up -> engine vacuum goes down to compensate -> paradoxically, slightly less fuel is used. The same could be said for inducing drag via removing the tailgate.

The worst part about all of that is that all of this is so wildly dependent on speed and engine loading and the power output of said engine, that it's next to impossible to exactly quantify the benefits of a given eco-mod for a gasoline-powered vehicle.

Now, for highway commutes, adding eco-mods generally gives the desired result. However, the old saying applies - Your Mileage May Vary. So, good luck and have fun with experimenting.
  Reply With Quote
The Following User Says Thank You to t vago For This Useful Post:
aerohead (06-12-2013)
Old 06-04-2013, 02:05 PM   #9 (permalink)
Master EcoModder
 
freebeard's Avatar
 
Join Date: Aug 2012
Location: northwest of normal
Posts: 27,562
Thanks: 7,738
Thanked 8,554 Times in 7,041 Posts
Quote:
The fronts, which don't have ABS, most decidedly have locked up before. Big smoke, very scary.
  Reply With Quote
Old 06-06-2013, 02:15 AM   #10 (permalink)
It's all about Diesel
 
cRiPpLe_rOoStEr's Avatar
 
Join Date: Oct 2012
Location: Porto Alegre, Rio Grande do Sul, Brazil
Posts: 12,548
Thanks: 0
Thanked 1,622 Times in 1,447 Posts
No wonder race trucks usually have either a tonneau or the tailgate removed...

BTW is your Dakota fitted with regular ABS or just an LSPV valve on the rear brake lines? I remember Chevy used to advertise the LSPV as an ABS in some of its Brazilian and Argentinian trucks...

  Reply With Quote
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com