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Old 05-31-2011, 07:50 AM   #1
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weight vs mileage

I have an f250 diesel. In market for new 5th wheel. How does weight affect mileage (7500 lb dry wt in Cougar High Country 299rks vs 10,575 in Jayco Eagle 321 rlts). Also any other feedback on these 2. Thanks!

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Old 05-31-2011, 12:02 PM   #2
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In my humble opinion I believe weight has very little to do with fuel mileage. What will effect the fuel mileage is the height of the unit. If one unit is 12FT tall and the other is 13FT that is one more foot of sail to move down the road. Another factor that will effect fuel mileage is speed. You will use more fuel at 65 MPH and above then if you drive 55 MPH. Simple fact of life, Speed equals money spent.
I get a consistent 12.5 MPG with my trailer and truck, but I drive 55 to 60 MPH and no faster. My trailer tires are speed rated for only 65MPH they are ST tires.
Jim W.

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Old 05-31-2011, 12:16 PM   #3
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I agree with Jim with one addition, the design shape of the RV also effects mileage.
2007 Newmar DSDP 4023
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Old 05-31-2011, 06:53 PM   #4
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Ditto both replys. Pulled a 24' TT, a 30' TT, and now a 35' Fiver, all with my previous Chevy 3500 Dually with Duramax/Allison. Saw next to no difference in mileage, the two TT had about the same frontal area, the fiver has more, but it is much more aerodynamic than the TTs.
2011 Chevy Silverado 3500HD LT Ext Cab 4x4 Duramax/Allison, 2016 Redwood 39MB, Disc Brakes, Mor/ryde IS, GY 17.5" H tires, 5.5K Onan, Dual ACs, auto level, auto sat dish, stacked washer/dryer, residential fridge, King sleep number. Michelle & Ann
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Old 06-01-2011, 05:11 PM   #5
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Appreciate the feedback. Now the hard part is deciding which unit to buy.
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Old 06-01-2011, 05:52 PM   #6
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One other thing you may want to check into is that the Jayco Eagle does not exceed your weight limits for your truck. I don't know about Ford but on my Dodge 3/4t diesel that Eagle loaded would push me well over the limits for the truck.
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Old 06-03-2011, 08:06 PM   #7
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I agree with the other posters that weight does not necessarily play the ultimate role. I had a 30ft Trail Sport travel trailer that weighed 4200 lbs and moved up to my current fifth wheel at almost twice the weight, but get the same gas milage that I used to. The Chaparral is more aerodynamic, I keep the speed below 60 and still get the same 11.5-12mpg that I used to. Good luck with your choices.
Ron and Debbie Parker, La Porte, TX
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Old 06-04-2011, 01:25 PM   #8
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Thanks for the information. We're still long way from deciding on the class of RV, much less looking for the right rig. Fuel economy is obviously an interest, although not the primary one. Getting good numbers for FW rigs seems to be a challenge.

Weight seems to be a factor, as does wind resistance. Heavier rigs seem to also be taller, and how much the fuel use goes up for each seems to be a question. Since we're interested in something for full-time use, we're looking at larger (heavier and taller) rigs. In fact, I suspect that if we go with a FW we'll be looking for something on the order of an F450 or F550. I've been told that such a combination will get 9-10 mpg when towing. Since the frontal area and weight are similar to a MH, it sounds reasonable that fuel use will also be similar.

Again, I have NO personal experience on this. Those of you who do have the experience, please share your knowledge with those of us who are still learning.

Thanks in advance.
David, kb0zke
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Old 06-04-2011, 07:56 PM   #9
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7-9 mpg towing 17400lbs with the 450.
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Old 06-04-2011, 10:54 PM   #10
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I won't disagree with the other opinions. I will give another perspective. I have an equipment trailer that weighs 6K empty and is only about 30" tall. It diffinately lowers the milage over the empty truck. Load a couple tractors on it there probably is not too much more wind resistance but lower milage. I put my 8.5' slidein on the truck at about 3K load, I will get about the same milage as with the before mentioned loaded trailer.

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Old 06-07-2011, 04:53 PM   #11
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Originally Posted by wrajha View Post
I have an f250 diesel. In market for new 5th wheel. How does weight affect mileage (7500 lb dry wt in Cougar High Country 299rks vs 10,575 in Jayco Eagle 321 rlts). Also any other feedback on these 2. Thanks!
The High Country is not available with dual pane windows or 50 amp service (with 2nd A/C prep). The gray exterior results in significantly higher exterior and interior temps as measured with an IR gun and the inability to support a 2nd A/C could be a big problem depending on what temps you camp in. The cable type slideout mechanism helps reduce weight, but also has some potential issues. Also suggest you join the KeystoneRV forum and learn more about Keystone customer support, the good and the bad. For these reasons, I walked away from the 299RKS. Didn't consider Jayco because it was too tall to fit under my RVport, but Jayco is generally regarded highly.
Larry Day, Texas Baptist Men volunteer
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'17 Puma 351THSS toyhauler
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Old 06-08-2011, 05:50 AM   #12
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Thank you. Much to consider. We're now looking at some Forest River lines.
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Old 06-14-2011, 04:59 PM   #13
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The formula for power required in a motor vehicle is Power = (A x Weight) + (B x Speed ^ 3). The last term is the wind resistance part and yes, that's Speed times Speed times Speed. It takes 8 times the power to go 100 mph as 50 mph in a given vehicle.

These two factors are usually about equal at 55 mph (that's why the 55 speed limit during the oil embargo since above that speed the wind resistance is the dominant factor, by far, in fuel milage.

So the weight affects about half the power requirement at 55, so if you doubled the combined weight of your trailer and truck, you would expect to need about 25% more power from your engine, requiring about 25% more fuel. Your increase in weight is considerably less, and you can do the calculation.

Google something like "vehicle power and wind resistance" to find more detailed versions of this formula (which is really important to race car builders, amoung others).
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Old 06-23-2011, 10:01 PM   #14
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We went from So Cal twice with an Alpenlite (14,000K) and once with a Colorado (8900K). Big difference. Went from 9MPG to 12GPM. Not much difference in milage, but the stress factor was less. Remember, all roads leaving CA are uphill and all roads entering CA are uphill also. I would personally have a lighter rig and enjoy the cocktail in the evening. Don

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