RTT and better gas mileage

Not quite. They tested fuel mileage with tailgate up vs down and found no measurable difference. This has been tested repeatedly by just about every truck publication since the fuel shortage in the 1970's. Same with a cap and Tonneau cover. The conclusions are somewhat mixed. In some cases there were slight improvements, in others fuel mileage was slightly worse. But in no case were the gains or losses significant.

There have been some tests done showing measurably better fuel mileage with the tailgate completely removed. With or without a net in its place. Stranger things have happened. To my knowledge no one has tested this with a RTT. My logic says it won't matter much and if anything may reduce fuel mileage slightly. But I've learned to never say never until the theory is tested.

 

Definitely this. Weight actually has little effect on MPG unless it's stop-&-go driving (once you get the weight moving, it takes little energy to keep it moving).

Years ago I had a Ranger pickup (longbed) with 4" lift on 33" tires (actually still do, but it's parked now). It normally got around 20-21 MPG on the highway with the bed empty (doing 60-62 MPH). When I had my Suzuki Quadsport 250 ATV in the bed, I noticed my mileage shot up to almost 25 MPG (I also added an extra 5 PSI to the rear tires when hauling it long distances). I couldn't believe it, so I had to repeat driving around with & without the quad in the back several times, and it was consistent... A slight bit under 21 MPG w/o, a pretty consistent 24 with.

 

I likes your post but a word of caution...
There are not too many here who have had fluid dynamics. So, big words and big concepts are not going to be a big hit. However, there are a lot of really smart people here who understand, intuitively, fluid dynamics even though they didn't take that class.
Really smart guys here. The dumb ones weed themselves out pretty fast lol.

 

I must respectfully disagree. It doesn’t matter how smart you are. If you haven’t taken a class, read some books specifically on the topic, and done the math, you really do not know how fluid dynamics work. Understanding some of the concepts is one thing, making predictions on specific geometric configurations of specific fluids in specific regimes, nope, not without a solid background, data and/or modeling.

 

I am 60 yo and disagree. Some innately understand.

 

What are you basing this opinion on?

 

I have a masters in aeronautical engineering and worked in a fluids lab while in school - I don't know shit. So I fully agree with you, fluid dynamics is stupidly complicated and ripe for dunning-kruger folks. I can take a few guesses as to what's happening, but yeah, that's all they'd be.

I have a copy of An Album of Fluid Motion on my bookshelf, I'll go see if they have flows around an RTT in there.

 

Had a similar experience in my Tundra when I put mine one. I just chalked it up to the RTT being mid height and working some magic in aerodynamics, and aerodynamics have a way bigger impact than a couple hundred pounds. My increase was constant as well, so all the "scientists" who say it's impossible or a myth can think as they like, but it happened.

 

He's older than you, so he knows more than you. His experience, recall, and wisdom trump any of your experiences, evidence that clearly refute his claims, or anything else that would mean he might learn from you.

 

pull muh finger, that there's my fluid dynamics =). after dumping a dozen k on your rig, the price of gas and mpg is a small consideration other than you are faced with it on a daily or weekly basis. The real question is, one or two gas cans?

 

Hmm...did you put the tent on once it started getting warmer? Like maybe around the same time "summer gas" hit the pumps?

 

This thread is full of hot air, which is lighter than cold air, and may account for the OP’s increase in mileage.


Happy Friday.

 

Facts.

So he has explicit training and experience in the discipline of fluid dynamics, which is exactly what I’m saying is required in order to speak accurately on the topic.

 

@Cetacean Sensation is not who you quoted in the post I commented on. I was referring to @hiPSI implying that being 60 years old granted him expertise.

 

Yes, I know. That was a multi quote where the first and second comments had nothing to do with each other.

HiPSI has training and experience in fluid dynamics. Look at his name and profile. Engineer. That’s my point. You have to have training and experience in this discipline in order to speak accurately on it.

 

Aaah, I didn't see that anywhere. Guess that makes me the dunce. Sorry, @hiPSI

 

I was a nuke engineer during my younger days and ran submarine nuke plants for the Navy for 10 years. We had a deep understanding of heat transfer and fluid flow (HT&FF) dynamics and air is definitely a fluid! Thus I too am somewhat qualified in saying that typically you cannot add additional drag / friction to a vehicle and have fuel economy increase.

But as others have said, fluid flow dynamics are difficult to predict in some cases. Maybe the RTT is acting as an airfoil and causing the truck to lift slightly and reducing friction between the tires and the pavement? (Trying to help you out here OP! )

Carry on!

 

Did the mix of city/highway stay the same or did the move result in more highway miles? My results vary a few mpg because of this and also what hills I have to climb at the endpoints. Grades suck way more than the miles of flat and even short hills of 300-500 feet or so make a big dent even if the distance is less than a mile. Is the RTT on the cab, a cap or mounted lower on bed bars? Lots of factors to consider but it’s easily possible to get a positive change even with more weight but I’d be skeptical of concluding that the weight alone was the sole factor or that every type of mounting would have the same effect on drag.

 

Not enough data to make any conclusions. Common sense does not suggest more weight and boxier shape = better mpg.
But certainly creates a lot of questions
How did you calculate your mpg?
Did you get your 1st batch of summer gas vs winter?
I put a RTT on my truck and watched my mpg sink to ~12-13 with similar driving behavior/terrain.

I have also been in the CFD (computational fluid dynamics) world since 2004. CFD simulation can nail real world (has it's own complications) results, however, it's often used for 'trending' data so engineers can get all those "what if" scenarios out of their heads