Tonneau Cover Improves MPG

Monday I installed a new Access roll up tonneau cover. The install was easy and everything went together well. I bought it from 4Wheeleonline.com shipped for $359. I noticed on my first 10 mile trip my ultragauge went from 20.8 to 21.0 MPG. Apparently the drag factor of the open bed does eat some gas. Now on to a power tailgate lock.

 

I think you are probably right...and it finishes your truck nicely!!

 

I've heard that's BS, but hard to say after one short drive. I'd like to see you keep track for a while though. Good looking cover!

 

I'll keep track of it and report back.
Bill

 

Thanks. Yeah, I put a cover on mine in July, and have not noticed any gains really. But I don't have a scan gauge to see instantly.

 

If you browse a bit, you can find a university study of several cover/cap solutions. The students used purchased products and makeshift items. Combination of roofline spoilers and full covers proved to be the most efficient configurations. I'm sure I hooked into the study at a couple sites I frequented. With time I could find it.

 

Gains are modest: perhaps up to 7% but most will be half or less.

 

Statistically insignificant.

Through all of the ups and downs, my average has never moved more than 0.2mpg on either Fuelly or my Ultragauge.

You can't accurately track MPG improvement that accurately over 10 miles.

This is 49 fuel-ups

 

Good to know, nothing to write home about.

 

Here's a link...to a link.

http://www.cleanmpg.com/forums/showthread.php?t=41763&highlight=tonneau+cover&page=2

The study was done by students at Texas Tech.

http://www.trucktestdigest.com/TTDfeatures/FeatureTailgateUporDown.htm

And to another article.

I wish I kept the links to the sites I've visited over the years. Most studies are nonscientific, so it's based on seat-of-the-pants calibrations and qualitative asessments. I have a tonneau on my Tacoma and I've not taken it off to do comparative assessments, but I like the look and keeping things dry. I was looking at one point to put a cover on my Ranger back a couple of years ago...but I had a rack that I used often, so I never purchased one.

 

Great article about the gates and covers. I once heard a GM engineer say the gate up catches some air and pushes it forwards towards the back of the cab, making a pocket of high pressure that "pushes" the truck forward. This would not happen with a tonneau, so I bet any benefits from uniformity come out in the wash.

 

Doesn't exactly push the truck forward, but it does create a "bubble" of pressure in the bed that acts as a spoiler of sorts to channel the air from the top of the cab over it and down to the tailgate.

Open your rear slider, toss a soda can in the bed, hit the freeway, and let me know how long before the guy in the middle seat gets smacked in the back of the head by the can

The "cargo net" tailgates are the worst.
They don't retain enough pressure to allow the bubble to form, but they have more drag than 50% of the stock tailgate.

 

Come Spring, I might pull off the tonneau to see if the 'bubble' is the way to go in catching extra MPGs (or slivers of a gallon). But while it can snow, I'll opt to keep it on. I hated shoveling out the Ranger back in the day, but i didn't want the extra weight of ice/snow

 

I can go from 20.8 to 21 by slowing down from 65mph to 63 mph. Or, the wind changes by that amount.

The tonneau does help a lot in heavy crosswind when that 'bubble' just gets blown away. I use to have days when I'd set my cruise at 55 mph and be sitting at 15 mpg just because of a 25mph crosswind, but once the tonneau went on that quit happening. Besides, Murphy's law dictates that if mpg takes a hit when wind comes from the left, front, or right, then you'll never see a tailwind in your life.

 

Was that Murphy, or Joe Isuzu (mid 80s commercials)? I recall the commercial bragging about the cars ability to go some huge top speed and get the economy of today's hybrids (going down hill in a hurricane).

I'll bet where the plains are large, crosswinds really become part of the driving phenomenon. Luckily here, the trees knock the wind down a bit, but on the highway where it gets closer to L.I. Sound, you can feel those crosswinds.

 

I installed a Roll-N-Lock and noticed a 1-2MPG improvement. I fill my truck twice a week so I notice....

 

Mythbusters proved this makes no difference...

http://dsc.discovery.com/tv-shows/m...atabase/driving-tailgate-fuel-consumption.htm

 

I had a tonneau for a while and noticed a slight gain, nothing significant. I noticed my average MPG's climbed from 17.5 to just over 18 with the tonneau. I'm doing even better with my fiberglass shell and consistantly pushing 20 MPH. I generally drive the same route, similar traffic situations week to week. I liked the tonneau but I didn't and wouldn't buy one if your primary reason is MPG's.

 

They simply proved that the tailgate up actually does improve mileage over tailgate down. It has nothing to do with a cover on the bed.

As mentioned, with the tailgate up, the air that passes around the sides of the cab and the top of the cab will strike the tailgate and swirl back causing a "bubble" of air type effect. This causes higher speed air that travels over the cab to glide across the "bubble", and over the back of the tailgate. This reduces wind drag, and has the best MPG over tailgate down, which creates drag on the back of the cab/bed area.
With a bed cover (Be it "cloth" or a hard cover) the air that travels over the top of the cab now swirls behind the small section of the cab, and as it passes over the edge of the tailgate, will swirl there as well. This in essence would create two places of "drag" (Albeit small areas) where the open bed would only have one. (The area behind the tailgate, on the outside)

Theoretically then, a bed cover would actually increase drag but by a very small amount. It will be interesting to see if the OP gets long-term fuel economy gains. No way to truly tell over 10 miles. Heck I could change my driving by a small amount and gain 1 MPG if I wanted. lol. Keep us updated OP!

 

Not doubting you, but I'm very surprised that you have a gain with a fiberglass shell. I would think the weight if that would negate any gains from less drag.

With that said I haven't had any gain with my tonneau cover.