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Fifth wheel mileage question

Fiver owners, not trying to start a debate, but wanted some data to think about.
I have a 2017 f350 Dually diesel and I am looking at fivers in the 30-35’ range but the weights vary quite a lot I’ve seen 30’ at 9k lbs gvw. and 35’ at15k lbs. gvw
my question is will it make much difference in mileage pulling those different weights, and length trailers or is this a aerodynamic issue nor so much weight. ??

Explorer II
Explorer II
My last 6 trips or so have been traveling the exact same 350 mile route going to visit her aging mother. I average between 8 and 13 MPG a trip. The only difference is the wind. This is with a gasser however
2011 Ford F-150 EcoBoost SuperCab Max Tow, 2084# Payload, 11,300# Tow,
2013 KZ Durango 2857

Weight matters. Getting an extra two and half tons moving in stop and go traffic requires a lot of energy or fuel. Pulling an extra 5,000# up a hill also takes a lot of juice. Weight also matters when it comes to stopping your rig as retarding all that extra momentum will create a lot of heat energy which needs to be replaced as fuel.

I always strive to always keep my weight down as much as possible by loading lightly and leaving unneeded stuff at home. Lighter rigs are easier on your truck's drive line components and will result in fuel savings. Whether the savings are that important to you is something you will have to decide.

I'm of the opinion that blaming aerodynamics as the major source of poor fuel economy is a rationalization for towing heavy.

Explorer II
Explorer II
2012 F-350 CCSB SRW 6.7 3.31 axle. 24' box 6500 lb., 27' fifth wheel 9400 lb., & 37' fifth wheel 13,500 lb all have averaged around 11 mpg. I believe that aerodynamis is most significant effect on towing mileage.

This is our 1st long trip with our new 5er, 14k gvwr. We've gone from so. NV to Reno-Elko-Boise-Lakeview-Medford so far. Tow vehicle is a 2017 Ram with Cummins 6.7.
We've driven from hot desert to high mountains and everything in between from 2700ft elevation to 7300 foot passes.
MPG has been anywhere from a high of 12.2 to 9.3.
Just say no to the payload police :C

Explorer II
Explorer II
We usually averaged between 11-12 mpg towing our 12,000 lb. 5th wheel. We averaged around 10-11 mpg towing our 15,000 lb. toyhauler. Same truck, same height, same width, heavier trailer.

IMO, I'd be more concerned about length rather than weight. Length will affect your RV site choices.
Howard and Peggy

"Don't Panic"

Nomad II
Nomad II
Aerodynamics are the biggest issue but particularly in hilly/mountainous terrain, weight will have an impact.

GVWR is a good surrogate for what to expect the trailer to weigh. They don't put bigger beefier axles on unless they need them. You won't find a big difference in weight between trailers with similar GVWR. About the only exception I can think of would be if you compare a toy hauler to a standard 5er but don't take any toys. The toy haulers are designed assuming a fairly significant load in the garage.
Tammy & Mike
Ford F250 V10
2021 Gray Wolf
Gemini Catamaran 34'
Full Time spliting time between boat and RV

I agree with the person who said heavier FWs often equate to quality. I also agree with the two that said, don't sweat about the mileage; pick the floor plan that works best for you. On that, I have to add that after four travel trailers and knowing what we liked and didn't when we started looking for an FW, we had every salesperson bring the slides in so we could see what that felt like as far as walking around when we stopped at a rest stop or had to spend the night in it that way at an overnight stop. That was an eye-opener. In our FW, we can access all kitchen appliances, the commode, and can sleep in it, all with the slides in. Good luck in your decision.
2011 Bighorn 3055RL, 2011 F350 DRW 6.7L 4x4 Diesel Lariat and Hensley TrailerSaver BD3, 1992 Jeep ZJ and 1978 Coleman Concord Pop-Up for remote camping
Dave & Renee plus (Champ, Molly, Paris, Missy, and Maggie in spirit), Mica, Mabel, and Melton

I would not be overly concerned with the weight/height but really concerned with the floor plan I wanted. Most fivers run 13 feet and a few inches to top of a/c's regardless.
Now your mpg will run 9.3 to 10.5 depending on the terrain and more importantly your speed. I had a F-250 diesel pulling a heavy 28 foot Sunnybrook fiver and ran 10.5 fairly consistently. Our 40 foot motor home with a cummins got 9.5 to 10.5. Now with the setup in my sig I get 9.3 the majority of the time. I run 65ish on interstates and 59ish on primary roads.

I will stress again though, go with the floor plan that you want or you will be sorry a few months, years down the road.
Camping Hoss
2017 Open Range 3X 388RKS
MorRyde IS with disc brakes
2017 F-350 6.7 with hips 8'bed
Lucie our fur baby
Lucky 9/15/2007 - 1/30/2023

My experience is weight makes very little difference in MPG. My 5er is about 12,000 pounds. I often tow my 3500 pound boat tandem. MPG is about the same either way. And it doesn’t really matter if I’m towing relatively flat (not much of that in Colorado) or through the mountains.
2012 RAM 3500 Laramie Longhorn DRW CC 4x4 Max Tow, Cummins HO, 60 gallon RDS aux fuel tank, Reese 18k Elite hitch
2003 Dodge Ram 3500 QC SB 4x4 Cummins HO NV5600 with Smarty JR, Jacobs EB (sold)
2002 Gulf Stream Sea Hawk 29FRB with Honda EV6010

Rig in my sig. 50,000 miles. Average 9.5. Been as high as 12.1 as low as 8. Sometimes the mountains are steeper, sometimes the wind is at your back.
17 DRV MS 36rssb3
17 F350 King Ranch CC DRW 4x4 6.7 4:10 B&W hitch
“A good traveler has no fixed plans, and is not intent on arriving.” Lao Tzu

You’re driving habits will also dictate the MPG you get..

I can tow my 16,000 pound fiver and get just shy of 12 MPGs and the very next trip get just under nine to the identical campground.

Wind, speed, acceleration, all will alter your numbers
Me-Her-the kids
2020 Ford F350 SD 6.7
2020 Redwood 3991RD Garnet

Weight matters more as to the overall build quality.
"If I'm wearing long pants, I'm too far north" - 2oldman

Yes I wondered if it made much fuel mileage difference between lighter rigs or heavier rigs. it doesn’t sound like much. Pretty much get the one with the floor plan you like and drive.
Didn’t want to be surprised and find out I’m getting 7-8 MPG….??

Explorer II
Explorer II
Speaking from over 44,000 miles towing fifth wheels with diesels: on the flats, once you get it rolling, it's wind resistance (think pulling three sheets of plywood through the air at highway speeds); in the mountains, weight really comes into play. Significant headwinds or tailwinds and all the above go out the window. When we upgraded our rig 2-1/2 years ago, the GVWR (and actual weight) of the trailer increased from 13K to 15K lbs. Overall there was about a 1.5 MPG difference coast-to-coast in all kinds of conditions. With both trailers, I saw mileage as low as 4.5 MPH (45 MPH headwinds)/8 MPG (6% grades) and as high as 15 MPG (45 MPH tailwind in the Central Valley in CA). Bottom line is, it just depends.

On the other hand, not many people buy large RVs and worry about fuel mileage.

U.S. Army retired
2020 Solitude 310GK-R
MORryde IS, disc brakes, solar, DP windows
(Previously in a Reflection 337RLS)
2012 F350 CC DRW Lariat 6.7
Full-time since 8/2015