MPG FAIL - Not so much fail!

OK.. so we all know slowing down helps when towing, but damn, I was surprised it would (with another style change) help by 20+%!  (MPG FAIL is my license plate   )

Truck is my '04 2500, 3.73, modded stock airbox, dyno tune, 93 octane, and a cat-back exhaust.  Front is leveled, and I'm riding on 275-55/20 LRR tires. (General Grabber HTS).  Trailer is a 7x16 flat-nose, extra-height Car-Mate enclosed with a high-profile A/C on the roof (OAH: 9'3"), only weighing around 5k loaded, but has bad aerodynamics.

My previous style (That I've been using for close to 2 years with the same setup) was this..  Cruise control set at 70-75.  When approaching a hill, I'd lay into the throttle so that the Inst. econ read 6-7 MPG, which is the most throttle it'll accept in OD without downshifting, and disengage the cruise.  If the speed dropped by more than 2-3 mph, I'd downshift to 3rd, and try to keep the inst. econ at 4 MPG or above.  In PA and surrounding areas, there are lots of short hills followed by more short hills, so there's a LOT of uphill, downhill, uphill combinations.  Going downhill towards another uphill, I'd hold the throttle at 6-7 MPG to make a run at the next hill, letting the speed run up to a max of 75-80, so hopefully keep it over 70 by the top of the next hill.
That style gave me a very consistent 8.2-8.6 MPG as average, and on a trip that the GPS says would take 3:30 (hr:min), it took 3:30.

Lately, I've been trying this..  Cruise is set at 65-70.  When approaching a hill, I still roll into the throttle to the 6-7 MPG reading, but now, I let the hill drag the speed down, trying my best not to let it downshift.  If the speed drops to under 60 (usually right around 56-57), I will downshift to 3rd, but keep the inst. econ at no less than 5MPG, usually shooting for 6 or above.  Going downhill for another uphill, I roll into the throttle to the 7-8 MPG reading but won't let the speed go over 75.  Basically, I'm driving more like the semi trucks.

This style has netted me no less than 10.2, often 10.5, and as high as 10.8 MPG.  Trips that are said to take 3:30 take 3:45.

I'm absolutely blown away that trading off a 7% time increase nets me over 20% in economy.

Picture of truck & trailer for reference:
https://goo.gl/photos/WtmvtwYtTULb81Wx5

Funny how that works out, pulling a box the wind resistance will kill the mileage.

Interesting.

So my question would be, how much actual fuel did you save and was the cost of that fuel worth 15 minutes of your time?

I do not have an answer to that question, but I was just curious as to what you thought.

I wonder if something like this would help, it's made by www.nosecone.com

This style has netted me no less than 10.2, often 10.5, and as high as 10.8 MPG.  Trips that are said to take 3:30 take 3:45.

I'm absolutely blown away that trading off a 7% time increase nets me over 20% in economy

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Of course, .6 or .3 MPG is negligible.

Need to get yourself a '79 rabbit diesel and pull with that. You'll do better with the mileage.

I gave up figuring mileage on my AV a few years back. Wasn't worth it.

Pulling 10K lbs my 4.10 equipped with hyper tech regular fuel program, I got 8 mpg average for the 2300+ mile round trip to Disney and back. averaged 65-70 mph most of the time.

I've got 34's with 4.56's and a 6" lift and I average 14ish mpg combined city and highway with a Bully dog GT set on performance tune lol.  I say 14ish because it would be higher if I did strictly highway of course.

I'm about where cadboy1 is 8 mpg, but I do take a run at hills. If you ever have taken I75 down through Kentucky and Tennesse you know what I mean

EXT4ME said:

So my question would be, how much actual fuel did you save and was the cost of that fuel worth 15 minutes of your time?

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On my trip that took an extra 15 minutes, I saved 5.3 gallons of 93 octane.  at $2.85 a gallon, that's $15.23 each way...  Or, another way to look at it, $15.23 every 15 minutes = $60.92 an hour.  I don't make that much at work..    $30 on a round trip is worth it to me - that's a free case of good beer or a most of a bottle of decent whiskey! 

There's also the calming factor of just running in the right lane, not having to worry about not being able to get a good run at the hill for traffic, definitely not having to think about cops, etc.

PerfectReign said:

Of course, .6 or .3 MPG is negligible.

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10.2 to 10.8 is my current range.  8.2 to 8.6 was my previous.

20+% is not negligible for a 7% increase in time spent.

MS03 2500 said:

I wonder if something like this would help, it's made by www.nosecone.com

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Funny you mention that!  I had spoken with them a while back when I first bought this trailer.  Other than giving me the impression that they could barely be bothered to speak to anyone for a non-commercial account, with me towing ~4000 miles a year, the ROI was.. a long time, especially since we have plans for a class A RV to pull this trailer in just a couple of years, negating any benefit.

Also, I've read that much of the drag that comes from pulling a trailer is actually off the trailing edge, and the flat nose isn't as big of a problem as we had thought, since a cone that size doesn't significantly reduce the effective frontal area.
That research led me towards looking at the airfoil tabs, and even found 2 race guys that were using them - Neither one reported any meaningful improvement.
The "Trailer Tails" we've all seen on some OTR trailers seem to be beneficial, but I'm sure the ROI for a private party would be silly.

I was reading over at that website they claimed 20-30% increase which I know is BS. Now for the rear that is very true Even the AV has some serious drag where the air comes off the roof and onto the bed panels. Something similar is on my trailer but it is more for protecting the wrap around front window.

MS03 2500 said:

I was reading over at that website they claimed 20-30% increase which I know is BS. Now for the rear that is very true Even the AV has some serious drag where the air comes off the roof and onto the bed panels. Something similar is on my trailer but it is more for protecting the wrap around front window.

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I think I remember reading that the sail panels are actually quite important to control airflow from the roof to the bed, so the truck didn't suck exhaust gases into the cab when the midgate/rear window were out?  Cool stuff.

If my buddy's Suburban 2500 had the same mods, I'd like to borrow it to see what kind of mileage I get..  I'd bet it might be a little better!

Yup that's why they are holes in the sail panels, if you haven't tried taking the rear window out and drive it you will see a little increase