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.

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?

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.

Cannot... resist... urge... to ... post... link:

http://ecomodder.com/forum/showthrea...ery-11445.html

Resistance is futile.

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.

ideal attitude - thanks!
 

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.

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.

:)

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...

seeing
 

When Texas Tech did their pickup truck research back in 1988 the difference between tailgate up/down meant only a 1% change in drag on average,which would translate to only a 1/2% change in fuel economy,measured under extremely controlled conditions.
With all the variables of real world driving it would be very difficult to discern such a small difference given the signal-to-noise ratio.

FE for that tank is in, and we scored 19.24mpg. This is a new full-tank record for the Dakota, and by about a full mpg. It's also about 1.5mpg over the record for a pure commuting tank.

Now, possible alternative explanations. The weather, as I was saying earlier, is getting really nice lately. In removing the tailgate, my ruined bumper and the sandbags went with it, shaving probably close to 200lbs. One of my tires is having issues with air, so it fluctuated between 45psi, and 8psi during the tank. Average was probably 30psi but the truck pulled noticeably to that side when it was on the lower end.

This tank did include a road trip into the desert (evening trip so it was cool). Without the pressure of having to get to work, I was able to hold more economical speeds (averaged 50 or so, commuting usually 55 or so). I burned a huge amount of gas going over Mt Hood, but coasted in Neutral coming back, so I don't know how that changes the average.

This was also a compound-tank (went to the gas station once to top off for the desert trip.). This shouldn't affect anything because I added both fills together to the third decimal before dividing by total miles.

My next tank will suck because I'm driving really inefficiently and that tire is getting worse. When I get me new tires on (same type and size as before) we'll get another tank. Oh, and I'm due for an oil change, if that matters.

200 lbs
 

Just thinking out loud.When you removed the weight,is it possible that the 'rake' of the truck was altered ie.the tail went up a bit,giving it a relative 'nose-down' stance?

If this can be considered, the effect might be very low altough can be credited alongside the weight reduction and the resulting aerodynamic profile of the bed without the tailgate. Many small effects leading to a bigger result.

The rake did change a bit, but the rear only went up by roughly one inch, if that.

The next tank is in (I've been neglecting my log, so pay no attention to that). MPG for this one was 17.89mpg. That puts in in third-best ever for a commuting tank. First place at 19.25 is the one above with commuting and a bit road trip, and second place was 18-point-something with commuting and a 30mi hypermiling run. With the tailgate and full weight in place, at one point I tried to get maximum economy on pure commuting and got about 17.2, although that was with noticeably worse weather. Given that this tank had a LOT of driving like an idiot, I'd say that's pretty okay. The tire continues to plague me, and at least 50mi of the 320mi tank were done with one tire at 10psi or less.

When I get the new tire on, I'll start a new tank and we'll see where that goes. So far, the Dakota has set two top-three-ever tanks with the current setup.

200 pounds is a lot of weight. Dropping 200 lbs. could yield 1MPG all by itself. And one inch difference in rake can be a lot of difference, as its effect varies exponentially with speed.

This thread looks like a good place to dump this image :

http://www.autoblog.com/photos/2014-...#photo-5885423

If you look below the image there are additional thumbnails that you can open.

Now why isn't the image showing up ??? I am seeing a little blue box with a question mark in it. Using Safari.

Here is a direct link to the image : http://www.autoblog.com/photos/2014-...#photo-5885423

:confused: It looks OK
In Opera I see the <br />, but no placeholder icon.

If the pickup had a slant chop, even a stock height windshield, with the back lowered 2-3" the point where Templating begins would move forward 2-3'. The curve might touch the top of the tailgate.