Are you testing these results at the same speed with cruise on? Your foot can hold the same speed cruise can in a gear above while turning many less RPM's. Remove your tonneau or roll it up. If you're in a Lariat (the most accurate way to do this) try your message center with it rolled up and down and let the numbers level out. Your tailgate basically drafts behind your cab like vehicles do behind big rigs and their trailers but I'm sure there are gains to be had. Would you try doing this and letting us know. What kind of tonneau are you running as well.

 

Well, that goes against every study, from Cal Tech, MIT, Consumers Union, Popular Mechanics, etc.

What are your driving conditions/habits?

On my truck if I pop the Fold-a-Cover off, and drive the same freeway route I lose 1 mpg. Put it back on, the mileage goes back up.
Do to my need to drive this 200 mile route every month or so, sometimes with the cover on, sometimes with it off, I have 15 trips with the tonneau, and 4 without it. The 1 mpg is consistent.

What other mods do you have on the truck? Do some negate the tonneau? Example, most people put over size tires, aggressive tread, on their 4x4 trucks, which cut your mileage much more than any other mod may increase it.



Of course, the tonneau only has an effect on highway speeds.
Around town wind drag is not significant. At 65 it is very noticeable. At even higher speeds the results are higher.

That of course assumes the tonneau is sealed, tight, with no air catching edges.

Again, there are over two dozen findable scientific tests verifying the mileage increase on a tonneau.

The effect of a tonneau would be highest on an 8 foot bed.
The shorter the bed in relation to the height of the cab the less the effect.

Plus, consider, if you get 13 miles to the gallon due to truck configuration and driving style, then an increase of five percent is still 13 miles to the gallon...


Naturally, nothing overcomes a lead foot.
Chris

 

I honestly don't care what the studies say. Real world results ALWAYS trump the studies. I'm a software tester in real life so I know how to isolate variables as well as the next guy. I've read all those studies as well, and none have all the variables covered enough to be what I'd call accurate. The only studies you mention that would warrant any credit from me are MIT and Cal, again, i've read both.

I've driven with the tonneau on/off and I ALWAYS use cruise when on the freeway. On a couple of ~100 mile trips I've done there was NO noticeable difference in MPG. The biggest diff i've ever seen was about .25 mpg, which I personally don't consider a noticeable gain. You could get a .25 difference just depending on the wind on the freeway.

I drive like Grandma moses most of the time and my SCAB barely breaks 14mpg highway speeds with or without the tonneau. I avg about 14.5 on the freeway.

I don't have very many external mods at all. I have a Vent Visor hood protector, in channel vent visors, and a K&N air filter. My SCAB came stock with the LSD, and 3.73 gears as I recall.

The tonneau I had was a Extang Tough Tonneu as I recall. It was a snapless install and I've played around with the frame more times than I can count to get the thing as tight as can be. A soft tonneau that only has 3 bars (seems to be standard) just isn't firm enough to reduce drag.

Your fold a cover is much firmer than the "soft tonneau" that was mentioned here earlier like i'm referencing so I could imagine a SLIGHT gain with that cover. But a snap on vinyl cover, or soft cover like I had or anything similar I would love to see a REAL WORLD difference.

Either way, my extang was so absolutely useless as far as MPG is concerned that I picked up a Fiberglass canopy this weekend. At least I can put my dogs in back now The soft tonneau is great for covering things up, or keeping some things slightly hidden but it won't get you anywhere near the 2-3 mpg gains that Extang and other companies claim.

If anyone wants to buy an Extang tonneau let me know... it has less than 5 months of use on it.

later
Tarkin

 

Based on your report you were seeing about a 2% improvement.
You don't mention what other mods you have, I assume tires/wheels or something to get such horrific freeway mileage.

I get about a 5-6 percent improvement.
5% is the equivalent of a 15 cent a gallon discount.
My results match the tests, and others. I don't disbelieve you, but you are defiantly the exception to the rule.
It happens.

If you get 14 on the freeway, there is some other issue.
I have driven a SuperCrew XLT 4x4 with the 5.4 to Vegas and back.
I got exactly 18.0 going up 18.6 coming back. That is about what I would expect. My truck (4.6 mods, tonneau, 2 wheel, 18 inch rims, etc.) got 22.1 and 23.4 on the same run. Slight tailwind on the return gave me a tad more mileage. That is at an average freeway speed of 65 in both trucks. Too many CHP out there to cruise faster.
Cruise was used both times.
Chris

 

I don't mention other mods because there aren't any It's all stock otherwise...

At what I would consider a best case scenario such as yours, you're looking at 2 years to pay off a 250$ tonneau cover. In my case I'm looking at at least 4 years. I can get MUCH better mpg by riding my bicycle to work 2-3 days a week

In a worst case scenario such as mine you basically get a Net Advantage of Zero as I feel a 2% increase could easily be attributed to environmental factors. There were trips I actually did get +1 mpg BETTER with tonneau off. I have 6000+ miles on the truck with and without tonneau.

Obviously worth is subjective to everyone... But I personally don't feel a Soft Tonneau is going to net you enough gains to justify the cost.

My suggestion re: tonneause is don't buy one for MPG improvements, buy them because you want one

As far as Freeway goes, I really wish I could get better, but i've never come close to breaking 15mpg. It's pretty much a stock 05 STX SCAB 4x4 with LSD and 3.73's. I'd expected at least 16-17 highway, but I don't get anywhere near that unfortunately

Later
Tarkin

 

There is something wrong with your truck if those figures are correct, or something unusual in your driving habits.

So honestly, your results are based on a truck that gets far worse gas mileage than the average, the norm, or even the vast majority.

Thus your results are skewed.

You can not get 3 to 5 mpg less than virtually everyone else and then say that a mod did not benefit you. It might have, it might not. You would have to be getting somewhere near the normal mileage to even make a call.

Example, if you have one of the famous leaky injectors no mod you could do would ever get you to normal factory numbers.

Have you had the truck looked at by the dealer? Reflashing may be in order.

I run in 115 plus temperatures, in mountains, LA traffic, with California’s worse blend gasoline, and with my STX I get vastly better mileage (worst ever was 14.5 around town hotrodding it) and even with the XLT SuperCrew I was using for a couple weeks I didn't get anywhere near that bad. And I admit to thrashing it. Rental truck for a business I sometimes help out.

I really think there is something wrong there, and hope the dealer can fix it. That is just a little too low. Unless you ride your left foot on the brake or something (just kidding).
Chris

 

I think they not have an egg between the pedal and the foot, they have their eggs between the pedal and the foot!

 

I wish that were so Chris, and I do plan to have the dealer look at it. Sticker numbers are under "ideal" conditions so the chances of hitting those numbers in the real world is rare as is. I've read 20-30 threads on here, FTE and f150.net and a common thread I've noticed is the SCAB's seems to get much better mileage than the SCREW's.

The other difference in the trucks besides body style is the SCREW's generally seem to come with the 5.4 as opposed to the 4.6. I don't think that should make a difference, but maybe it's possible the 5.4 being newer is more efficient.

I dunno, but again, I think there are too many variables to say for sure where the real issues lays.

A soft tonneau regardless is just going to get folded and mangled by the wind as it drops down over the top of your cab. Mother nature is way more powerful than vinyl and aluminum. I could see that in my own use. I could actually see where there would be additional drag on the truck now that the "swirling airball" that is created in the bed of the truck is no longer there. I could actually see the tonneau be stretched down below the last cross bar.

Again, your tonneau is different, and I do believe you that it could make a difference. Most of the studies i've read also noted specifically that a "hard tonneau" is the way to go and I believe it. I personally just don't see any way a true soft tonneau is going to make a difference.

I only ride my left foot on the brake when I drive with my left foot, it's kinda hard getting it over the brake to the gas pedal:P

Later
Tarkin