Tonneau Fuel Economy experiment

It's not clear to me that this is his daily commute. I assumed he did these test runs as a test, not part of his daily commute. Who drives back and for between 2 gas stations for work?

What is it kencraw?

 

JCBigler, I think that would work if one's driving patterns were somewhat consistent, but mine aren't. I'll go whole tanks of gas puttering around a 10 mile radius in Roseville, but I also do a fair amount of road trips around the west-coast. Sometimes on those trips I tow a boat, sometimes I don't. Sometimes I'm alone and lightly loaded, sometimes I've got the kids and a bunch of gear. Eventually I could null it out, but it would take a lot more than 10 tanks and I'd have to specifically focus on a consistent set of usage.

Perhaps I can come up with a set of trips that I do that are consistent enough and if I make sure to fill up just pre and post trip, I could add some valid data to the mix. I'll give it some thought.

 

Yes, this was a special run, designed to pick something as consistent and variable free as possible, where I could just stay on cruise control as much as possible.

I have the joy of a 5 minute, 2 mile commute, so that's not going to work.

 

Mythbusters did this: http://youtu.be/r3aqHbD-O9E

Ray

 

Sounds like if you want a bed cover a lightweight tonneau cover won't hurt mpg and might slightly improve if you do a lot of highway driving.

To actually test and verify how much may be a lost cause on even the best controlled loop.

This guy has a lot of things worth reading on testing and other aspects of fuel economy.

http://www.fuelsaving.info/testimonial.htm

http://www.fuelsaving.info/power_economy.htm

 

Yes, I did mention that in my original post, but thanks Ray, for the youtube link. I tried to find it on Netflix streaming, but the select Mythbusters they had didn't seem to include this one. I was particularly interested to see what the mesh looked like ( how loose it was, how thick the mesh pieces were, etc.) and verify that the hard cover was indeed a tonneau and not a camper shell (it wasn't clear in any of the threads I read).

 

Mesh it is. Gives me an excuse to finally pull the trigger on the American flag mesh i've had my eyes on.

 

Leg 1 - 23.95
Leg 2 - 22.42
Leg 3 - 24.74
Leg 4 - 22.78

These differences are insignificant, and given the differences in temperature and speed, well within the margin of error.

Warmer temps help in multiple ways. One way is the engine is more fuel efficient with warmer are.
Another way (and granted, insignificant when we're talking a difference of 5 degrees) is another effect of cold air being more dense.... wind resistance is lower through warmer air.

 

I know Mythbusters seemed to think mesh was the way to go, but reports that I've read over the last 20 years is the opposite, and mesh is actually worse than tailgate down.

The mesh breaks the bubble behind the cab same as the tailgate down/off does.... and it replaces the tailgate with a sail.

 

I didn't do a very good job in my original post of stating my conclusions, specifically around the statistical significance, or said differently, the level of confidence I have in their precision...

I agree that we can't say with confidence that the Tonneau is worse. The deltas between the runs are small and could be explained by a number of things from temp to increased traffic to the small speed deltas.

However, I do think the experiment gives a fairly strong indication that a Tonneau will not give a 5%-10% improvement in fuel economy. That's what would have been necessary for me purchase one, so I consider this experiment to have been successful in giving the quality of results I needed.

 

That's a fair conclusion. Now jack those tires up.

I think you should have the 215/70/15 tires that are stock on the 5-lug correct? I run between 44-50psi on mine and have not had any handling/braking or uneven wear that most jump to as reasons not to even think of going over what the door placard says.

I did find that my oem firestones actually gave lower rolling resistance than my replacement michelin hydro-edge which claimed LRR with their "green-x". It has been 20k miles since I installed them and it seems they have slowly gotten a little better. I do a lot of coasting on my daily commute and it was pretty obvious that the coasting changed for the worse with the michelins. MPG dropped at least 2 mpg initially but seems to have come back up some.

 

x2 if you want mpg and don't spend time in the dirt. I keep in the mid 40s and it makes a fair difference. Besides my 245/75-16 dunlops are the only tire I've seen show high shoulder wear in a chalk test at 40 psi . Even if I go with a stiff ride at 51/48 the shoulders wear both front and rear (though they spin like crazy in the rain at that pressure, I can't run that high long term).

As for the tonneau, ultragauge tends to read near identical mileage when rural driving on calm days, better mileage on really windy days (much better in heavy crosswind, which is great for me because I get a heavy one off the lake most afternoons), mildly worse at city speeds, and mildly better when doing 65+ when the tonneau is out rather than rolled up. So much more to consider than tonneau on vs off.

 

THANK YOU!!!!!!

I've been preaching this for years and always get jumped on.

The only down-side is ride quality (and I prefer a stiff ride, and WTF, it's a TRUCK, not a Rolls Royce!).
I won't go over the sidewall max, but I'll go right to it.

Dry traction on pavement is not negatively impacted by increased inflation. People take what they know about off-road floatation and apply it to dry traction. Doesn't work that way.
Wet traction is not negatively impacted.
Again, people assume that a "hard" tire is a less "grippy" tire. That is true when it comes to the rubber compounds, but not to inflation.

A "hard" tire has less sidewall flex, so the tread does not roll off of the road... the tire maintains better contact.

Also, Navy tests at Pax river confirm that the speed at which hydroplaning occurs is inversely proportional to the inflation level.
I don't recall the exact formula, but at 28psi that speed is roughly 55mph.
At 35psi, that speed moves up to closer to 70mph.
This is assuming water depth no higher than the tread depth.

The chalk test is of marginal value.
It's okay for mall crawlers, but at high speed, the center of the tread will begin to "cup" inward (the same thing that contributes to hydroplaning), so even if a chalk test shows heavier wear in the center, that may not translate to uneven wear for a vehicle driven mostly on the highway.

I ran my BFG K/Os at their max rating on my Duramax, and at 35,000 miles I checked the tread depth. Perfectly even across the face of all 4 tires.

 

Worthywads thanks for the cover study. It was quite informative.

 

Done! Did it this morning, up to 46 PSI and then did the chalk test and found no uneven wear, so I'm going to stick with it. The ride is a tad more rough, but only at the high frequencies (which is of course no surprise) and nothing that diminishes the potential fuel economy advantages.

 

You should notice an obvious improvement.

I've gone as high as 60psi but just didn't notice enough to push it that high in the long run.

 

Yeah I've been a proponent of higher psi as well and have done countless chalk tests with no significant differences among wide ranges of pressures and definite mpg advantages. A more jittery ride but braking and handling do not seem negatively affected.

 

Yup.

Firmer sidewalls and less tread squirm will do that

 

There was a very scientific study done a few years ago that determined that the empty bed,with tailgate in place, got the best mileage. At freeway speeds the wind force sets up a circulating high pressure ball in the bed of the truck which drives the air higher over the truck bed and increases air flow. Adding the tonneau removes this high pressure circulation and the air flow drops down creating more drag. But the results are small in comparison to the natural air resistance of pushing that big box through the air. Ambient wind speed will have more affect. We recently took a cross country trip and had a tail wind for about 1000 miles going east, and a head wind on the return, in my wife's Highlander we got 26mpg with the tail wind and we got 19 mpg with the head wind.

My, new to me, 2008 PreRunner Sr5 will be hard pressed to match those figures at those speeds (75+) given that it presents a bigger face to the wind and it isn't geared to be happy at 75 plus.

For me, the reason to buy a tonneau is security for your tail gate and the contents. So I'll probably get a hard folding tonneau that will lock down and add the locking tailgate.

 

Mine actually seems to do better with the tonneau off as well. Right now its off for the summer mainly because of riding season, I always got my dirtbike back there, but it will go back on when I head for college this fall.