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Currently, I have no cap. Getting about 22 mpg highway. When towing 15 foot, 2800 lb travel trailer (not a pop-up) I get about 9 - 10 mpg highway. The camper is not very aerodynamic and acts like a sail.

The question is: has anyone else had this issue, and if so, did adding a cap noticeably improve gas mileage?

2011 Ridgeline RTL
40,000 miles
 

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Cap could theoretically reduce the frontal "blast" area of the trailer by blocking wind coming over the truck.... like very close slip stream effect.
I have no idea if this has any measurable effect in reality, but the big rig guys spend good money on similar "aero effect" products to smooth the air flow from their tractor to the trailer. Who knows?
I have read that tonneau makes no measurable difference; likewise with tailgate up vs. down.
 

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bed covers and tailgate down have no effect on mpg. I am certain this has been proven several times. if a bed cover improved mpg by 2 miles i would think every truck would come standard with one. getting a 2 mpg increase for Ford/Chevy/Dodge at the cost of $200 for a bed cover would be money well spent. same goes for the tailgate except it would become a dealer installed option. as for your trailer mpg dilema good luck. keep in mind that the cap will take away from your available payload.
 

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I have no experience with a cap....

I get HORRIBLE mpg's towing my small 5x8 enclosed with my Ridge. Even when it is empty it kills my mileage. When "Full" it only carries a 550# mower, trimmer,blower, and 10 gallons of extra fuel, so not much.

The front of my trailer is a big square box, that does not go easily through the air. A V-nose would liky do better but a cap would HAVE to help. The question is how much though?
 

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It would stand to reason a cap would help, but as to how much I could not be too sure.
 

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That is SO screwed up.
First they contradict the Title & findings with the write-up ("Tailgate up = Fuel Efficiency"... "Finding: Busted"): The article content says exactly the opposite of these Title/Finding statements. I believe the "Busted" was supposed to apply to "Tailgate Down = Fuel Efficiency", but the writer of the article screwed up the title!
Second (as if #1 doesn't give you pause as to the scientific validity of these backyard goofs), I would REALLY like to see these guys close the loop on variables & repeatability to bring real validation to some of the fun myth-busting things they do. All they'd have to do is add a couple of easy mods to their experiments, but they rarely do. In this case, it would be nice if they ruled out most of the vehicle/driver related variables by repeating the experiment, but switching trucks (swap which has gate up or down), swapping drivers (although this should be independently varied also), and by using cruise control on absolutely flat road (e.g. Bonneville flats?). See how close to the same mileage distance gap they get. That would be something to believe in.
I know it's just TV, but how hard would it have been to run the test twice with roles reversed??? Bad Science!
 

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Real life with Chevy and larger camper. With or without the cap my mileage did not change. Wind coming off cap still hits that big sail behind you.
In theory a spoiler on a cap will make better upward flow over camper. Of course the cap has to be able to handle the down force. A spoiler on the truck roof may be too far away to make a difference.
 

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My towing experience with leer cap an with /without homemade wind deflector
I got a small Jayco 145rb -2400lb trailer just 2 week before my vacation trip. trailer was raised ab 4" taller bc previous owner needed more clearance and switch leaf springs from under the axle to over. I made the wind deflector and install on the top of my leer cap. my trip was Chicago-IN-OH-PA-WA-VA-NC-TN-IN-Chicago Lowest mpg was 11.8, mostly 13 , highest on my way home in IN was 14.6 and 14.96 on regular gas. Average speed 62- 65mph following trucks, at safe distance of course. I didn't know if the wing helped at all. (I had honda element awd and a little pop up an never got under 19 mpg at speed of >75 (SD WY hi-way), at lower speed i often saw 22- 24 mpg) . However, I found something interesting on my last trip to Wisconsin Dells . I lowered my trailer so I expected better millage . It was short trip only 200 miles one way so I didn't bother installing my wing and I noticed immediately I had to press accelerator harder at 62-65mph, car would switch to fifth gear only when slightly downhill . My all trip was almost 3rd and 4th gear, average below 11mpg . I had no problem getting car into 5th gear on flats with the wing so I could drive at 62-65 below 2k rpm without any problems. The wind drag has a large impact on fuel economy. I think wind deflector works better with cap installed , deflector can be installed on very end of the truck so there is smaller gap between truck and trailer. I'm going to make new adjustable wider wing next year and ad some wind barker fins also consider trailer wheel wells removable covers .
 

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My towing experience with leer cap an with /without homemade wind deflector
I got a small Jayco 145rb -2400lb trailer just 2 week before my vacation trip. trailer was raised ab 4" taller bc previous owner needed more clearance and switch leaf springs from under the axle to over. I made the wind deflector and install on the top of my leer cap. my trip was Chicago-IN-OH-PA-WA-VA-NC-TN-IN-Chicago Lowest mpg was 11.8, mostly 13 , highest on my way home in IN was 14.6 and 14.96 on regular gas. Average speed 62- 65mph following trucks, at safe distance of course. I didn't know if the wing helped at all. (I had honda element awd and a little pop up an never got under 19 mpg at speed of >75 (SD WY hi-way), at lower speed i often saw 22- 24 mpg) . However, I found something interesting on my last trip to Wisconsin Dells . I lowered my trailer so I expected better millage . It was short trip only 200 miles one way so I didn't bother installing my wing and I noticed immediately I had to press accelerator harder at 62-65mph, car would switch to fifth gear only when slightly downhill . My all trip was almost 3rd and 4th gear, average below 11mpg . I had no problem getting car into 5th gear on flats with the wing so I could drive at 62-65 below 2k rpm without any problems. The wind drag has a large impact on fuel economy. I think wind deflector works better with cap installed , deflector can be installed on very end of the truck so there is smaller gap between truck and trailer. I'm going to make new adjustable wider wing next year and ad some wind barker fins also consider trailer wheel wells removable covers .
Very Interesting. It should be noted that you changed 2 variables when you got the lower MPG; the wing removed AND you lowered the trailer. I'm no aerodynamics expert, but it makes me wonder whether or not the reduced clearance between the trailer & the road would possibly have a negative impact on MPG (more so than the benefit of the shorter frontal sail)??? I'm not saying it would.... It just would be nice to see the change with just 1 variable changed at a time.
 

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I'm not an aerodynamics expert either but I've read a lot of articles that lowering "regular" car with rough under body produces less drag. I think it should apply to my trailer as well. I lowered my trailer b/c I wanted to "hide" it behind my truck so air can move over it smoothly. On my vacation trip I used the Torque (android app) to monitor engine load , mpg , fuel consumption/hr , engine temp, and other things but I didn't record anything, I didn't use it on my second trip so no comparison. Next time I use the Torque while experimenting with wing angle and I will attach ribbons to the front side of my trailer so that I can see and record how the air flows. I hope I find the right setup for my vehicles.
Here is another pic of my redneck creation :act014:. I just got yakima rails for my leer cap, so I can build something easy removable and adjustable (angle ,back and front) using my yakima setup.
 

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I'm not an aerodynamics expert either but I've read a lot of articles that lowering "regular" car with rough under body produces less drag. I think it should apply to my trailer as well. I lowered my trailer b/c I wanted to "hide" it behind my truck so air can move over it smoothly. On my vacation trip I used the Torque (android app) to monitor engine load , mpg , fuel consumption/hr , engine temp, and other things but I didn't record anything, I didn't use it on my second trip so no comparison. Next time I use the Torque while experimenting with wing angle and I will attach ribbons to the front side of my trailer so that I can see and record how the air flows. I hope I find the right setup for my vehicles.
Here is another pic of my redneck creation :act014:. I just got yakima rails for my leer cap, so I can build something easy removable and adjustable (angle ,back and front) using my yakima setup.
Outstanding.......... looks like fun. I hope your tweeking continues to yield better & better results. Enjoy those days out camping!
 
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