Taco Highway Gas Mileage - Tailgate up/Tailgate down

Tailgate makes no difference, covering the bed will.

There was an actual lab test done a while back, maybe not on a Tacoma, that showed that dropping the tail gate added to the rolling resistance. A low pressure area builds up behind the cab and increases the drag.

Brewster

Good question Dave,I have often wondered about this, although I have never personally tried it either way. What I have heared though is that putting the tailgate down can worsen your gas mileage. The reason being that when the tailgate is in the closed position the wind currents actually do not go into the box of the truck but pass just over top without hitting the tailgate. However when the tailgate is opened the wind currents push down on the box floor actually increasing drag to the tires to the road. I would love to hear anymore opinions on this, as I do a lot of highway miles commuting to work.

Just one data point here, but my 2000 2WD would get 2-3 more MPG on the highway if I put the tailgate down.

I don't know about my 4X4 because it has a fiberglass topper. I think the added weight offsets the aerodynamic advantage in that case.

Might want to try here :

eating TACOS from Highway stands give me gas

Is there a truck cap that is aerodynamically designed for the Tacoma?

Ellis

Brad P wrote:

OK, according to these data then lowering the tailgate does actually reduce the drag coefficient. So it _really_ is what seems correct actually is.

That's neat to know.

I thought that years ago, Car and Driver magazine did a test of various pickups with tailgate up/tailgate down, and the results were mixed. I believe the aerodynamic design of the vehicle as a whole impacts whether the tailgate position increases/decreases the drag coefficient.

I'd like to think that, since the truck structure is much sturdier with the tailgate up, that the vehicle's design yields the lowes drag coefficient with the tailgate in the up position. However, it sounds like real world data, at least for late model Tacomas, show otherwise.

MAYBE. I don't remember seeing at what speeds the tests were conducted. That could make a big difference.

-- Chris

Dave .. I've looked at this in depth (perhaps too deep!!) with my 93 toy SR5 p/u (4x4, ext dab, no ac, V6). After reading this you'll think I'm a nut, but so be it. Hopefully you you'll appreciate the effort.

Bottom line, I don't think you can't tell if gate-up or gate-down makes a difference.

I've driven my truck 27,900 miles. I always fill the tank, use a my debit card, and write odometer milage on slip (the slip always has total price, and price per gallon). To go that total distance, I've used 1,573 gallons. A resultant 17.73 mpg overall.

I've varied octane and seen no "statistical" difference in average mpg. I've tried "gate up" and "gate down", again, no significant difference in average mpg.

Interesting enough, there is one VERY discernable trend. Time of year. In the warm summer, mpg is higher 18.5 to 19.5. But in the cold winter (I live in MA) the mpg is lower, 15.5 to 16.5 mpg.

The problem with measuring your mpg, and trying to make an inference if something you've varied (i.e. octane, or gate position) has an effect, is inherently flawed. Even if you measure your milage with no othere discernable variable (same travel routine week to week, same gas station, etc..) your mpg will vary too much. Essentially you get TOO much 'bounce' in the mpg data. Something else is going on here. Either the vehicle's milage is very inconsistent on its own, or there are other variables playing a role. I suspect 'other variables'. As previously mentioned, air temperature appears to be a biggie. And no matter what your driving habits, even if they appear to be the same week to week, you can't control the weather (and in my case, in New England, you can't count on it being consistant at all).

I've been thinking of normalizing my data to "average daily temperature" to see how what that tells me. But hey, enough is enough. Plus, I then have to contend with mpg being calcuated ever 5 to 6 days when I fill up, and the avg daily temp being reported for each and every date. Sounds to ugly to get into.

I've discussed my temperature mpg revelation with a few people. Some were surprised. Others were not. One such acquantance used to work in the high performance engine field (typically drag motorcycles). Apparently, in the high performance world of engine's and racing, you can buy kits that "chill your fuel line". Seems maximum performance is gained by a hot engine being fed cold fuel. Temperature matters!

Anyway, with my truck, when I've varied octane, or gate-up or gate-down I can't see any statistically significant effects. My analysis of the variation in the data (not the average) suggest that it (variation) is the culprit here. You can't make inferences of averages if your variation is "excessive".

In retrospect, probably the only way to know for sure if gate-up vs. gate-down changes mpg, is to rely on lab testing, of your vehicle model. They have an environment that allows them to control all those variables that we on the road can't. As others in this newsgroup have pointed out, air resistance in the bed, that is specific to your vehicle's shape, also pays a role.

I found it interesting to read the role tire pressure plays. In my case, I don't think that plays a role in my data set, because I keep tire pressure constant. Or at least I try to. There again, air temperature can effect that (pv=nrt). [ .. Oh boy, don't what to go there.]

I also take anyone else's claims of "what does" and "what doesn't" matter with a large gain of salt. From my detailed, statistical, analysis, all I can find is very high tank to tank mpg variation that clouds the data analysis. Do other people "statistically" analyze their data variation?? I sincerely doubt it. So, are their results valid? Hmmm, somebody pass the salt.

I think we should stick to listening to the pros, from controlled testing. And even with that, the experts tend to disagree with respect to gate-up vs. gate-down.

With that all said, they way I look at it, with at least the gate-up vs. gate-down debate, the only thing that really matters is whether I want the gate up or down, for whatever reason.

My advice to you . . . forget-about-it. If you like your gate down - then go for it. (Just be careful when you parallel park!)

My last comment (yes, this has to end) - - - Yes I'm a geek. Who else would look at their gas mileage like this. If your wondering, professionally I'm a process engineer, and looking at processes and subsequent data is what I do. MPG with my first toyota truck was too much for me to pass up.

... RTS

I would! I'm an aeronautical engineer (by education, anyway) myself, and I also track my MPG via spreadsheet, noticing the same general trend you have regarding summer/winter variance. I think you're correct in your assumption that there are "too many other variables" involved in everyday driving to ascertain if the tailgate up or down makes a difference in MPG.

Even if you were able to control the temperature, wind, and other environmental factors, you'd still have to control other variables like vehicle speed--and then you'd still only have valid data for one circumstance (say, constant speed of 65 mph). Driving at any other speed MAY not produce the same result due to the properties of the airflow changing so much, meaning the tailgate-down configuration would work for one speed but not another, and who wants to keep pulling over and putting it up and down depending on temperature, traffic conditions, etc?

Only if the difference in MPG were large enough to overshadow the other variables would I stand up and take notice, but it doesn't look like it is. The change in MPG is likely more noticeable on inherently high-drag, low-gas-mileage vehicles like school buses and RVs. I once saw an RV with a modified front end--looked more like the space shuttle than a motorhome. I imagine he was getting a lot better gas mileage than stock--but then again even a half-mile-per-gallon increase is significant when you're only getting

-- Chris

i'll second this comment. i've done statistical analyses on gas milage on a couple of my cars. and i've never notices any stastically significant differences on milage when varying octane or gate up/down. one thing i did notice was the (apparent) increase in power when i had a tanneau cover on my truck. i had a '95 nissan with the 4cyl (read: no power at all but bullet proof). when i had the cover on i felt like i had more power (by seat of the pants measurements), but i never noticed any better gas milage.

you're temperature measurements make sence. i've noticed a bigger variation in gas milage with temperature with truck than with cars. i think it has to do with the grease in the cv joints and such being thicker and harder to turn when it's cold. i do notice that i get best gas milage in my car when the temperature is around 60 or so. i think that's because the air is dense and i'm getting more air in the engine at the colder temperature, but it's not too cold that it's adversly effecting the lubrication.

i also have one set of data points that vary octane with everything else held constant, but it's not enough data to make a conclusion. i've always heard that you'll get better gas milage with lower octane (until you start to knock) because the engine backs off the timing to prevent knocing and you get less power but better milage. well about a month ago i went on the same 800 mile trip twice in two months. the first time, my company was paying for the gas, so i got the high octane expensive stuff and got about 22 mpg in my subaru (actually quite bad, i ususally get 25 in the city, so 22 on the highway was bad). the next month, i was paying for the gas, so i got the lowest octane. everything else was the same (99% highway driving, cruise control set at 80, only one stop for gas at the 1/2 way point, temperature as close to the same as you could get) and i got 28 mpg. unfortunately i don't have more data to back that up.

Click & Clack addressed this question in 1997:

Tom - Vista, CA

Dave, running with the gate down will cost you more. Not is fuel, in fact, wind testing shows no advantage at all, but when it gets clipped by another car in a parking lot, then thats when it cost more.

Hmm. Seems to be a number of views either way on this but I think I`ll leave my gate up. One more reason to keep your gate up,in Toronto we have a Photo toll road, ie a camera takes a photo of your license plate when you enter and exit the highway and then you receive a bill in the mail. I hear lowering your tailgate blocks the cameras view of the plate thus no charge. I have heard though the police will charge those trying to ride for free in this manner.

Actual scientific study, excellent.

Brian

Something to consider: do they use reformulated gas in MA in the winter?

Otherwise, yes, this is pretty much how I look at my fuel economy as well. And yes, I do keep track of fuel and oil consumption for every vehicle I own, an excuse I can offer for our shared obsessive behaviour is that "a sudden drop in fuel economy or jump in oil consumption can be an early indicator of a problem."

GTr