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Old 12-03-2013, 09:45 AM   #1
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Towing TT with/without bed cap

I was wondering if anyone has done research into the difference into MPG with and without a truck cap. I was disappointed with 7.5 MPG that I got on my last outing, which was the first chance I had to run a full tank while towing. Last night I realized that my friends with TT's all have caps on the back of their trucks. I probably won't get one for the current TV as I am in the market for a newer one.

So, back to the question; has anyone checked their mileage with and without a cap?
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Old 12-03-2013, 09:49 AM   #2
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Makes no difference. Speed and frontal area of the trailer are the biggest factors in MPG. Next in line is motor size and rear end ratio.
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Old 12-03-2013, 01:50 PM   #3
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When we were pulling a TT, a full cab height bed cap, dis help the fuel economy ever so slightly. Then right after that, they made the switch to ULS diesel and the fuel economy dropped/

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Old 12-03-2013, 08:31 PM   #4
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Towed an empty 6 x 12 U-Haul trailer with a 4 cylinder Ranger and felt the drag and weight.
Loaded the trailer to the roof with my son's furniture and loaded the truck box with side racks.
To my surprise it towed much easier with the load.

I have found that side racks that I use often helps in towing.

BTW. We purchased our first 5th wheel RV 3 weeks after and towed it for 3 years with a Ranger STX 2.9L V6.
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Old 12-04-2013, 12:51 AM   #5
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Seems to me Trailer Life had a study years ago that came to "no conclusive results." I also think that some universite did some studies that came to the same above non-conclusion.
In other words, in the pickup world, toppers and air foils seldom make a measurable difference.
Tailgate up/down seems to make no real difference also.
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Old 12-04-2013, 08:03 AM   #6
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The factor that hasn't been mentioned yet is weight. Fiberglass Toppers weight about 300 lbs. Where they fill the void behind the cab and reduce the amount of stationary air that the TT front hits, their weight has an effect on fuel economy too. That 300 lbs also has an effect on your axle capacity as I encountered with my 1500 GMC. I was forced to remove the topper to keep it under the rear axle Max gross capacity to tow my TT. Solo my 1500 rode better with the topper, than without. Towing a lightweight motorcycle trailer I believe mpg was better with a topper but I don't have numbers to back it up.
The added capacity on 2500/3500 series may allow a topper. With a bigger motor, the topper may break enough wind off the front of the TT to make a minor difference, but a small gasoline motor in any 1500 series will be working hard enough already that no difference might be noticed.

Aerodynamics on big rigs shows improvement with trailer height cab extensions, but they are minor. So if fuel savings is your only reason to buy a topper, you may never recoup what you pay for the topper in savings.
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Old 12-26-2013, 01:15 AM   #7
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If you live in CA. you can save about $200.00 (depending on the weight of your truck) a year by putting a topper on your truck and registering it as a "permeant mount". No topper, you are required to pay commercial weight fees, which for me amounts to $200.00 a year. I did not see a difference in the mileage per gallon after I put the topper on.
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Old 12-26-2013, 10:08 AM   #8
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My F-150 SuperCrew EcoBoost with 6.5' bed and a Leer topper gets lousy MPG when towing a 20' TT that grosses about 4,870 pounds wet. Slightly worse MPG with a 5er that grosses about 8,000 pounds wet and loaded, and of course without the topper when towing a 5er. With either RV, usually 8 to 10 MPG @ 64 MPH, but strong headwinds and lots of ups and downs can push it below 8 MPG.

Caveat. I run regular unleaded most of the time, but switch to premium gas when towing long distances. I noticed about a 1 MPG improvement in MPG when running on premium, so the cost about breaks even.

When I ordered the F-150, I expected over 10 MPG when towing, so I'm a bit disappointed in my MPG when towing, but other than the same MPG as most other tow vehicles with those trailers, I'm extremely happy with my EcoBoost.

I like the topper to keep the weather off stuff in the bed. But it doesn't change the MPG enough to get excited about. Right now the topper is off so I can go to the RV store and bring home my 5er that's being repaired. It was drizzling rain when we picked up folks at the airport, and drove the 30 miles home with a bed full of luggage. We made it without ruining anything in the luggage, but that reminded me why I like the topper.
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Old 12-26-2013, 06:25 PM   #9
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Makes no difference. Speed and frontal area of the trailer are the biggest factors in MPG. Next in line is motor size and rear end ratio.
Agreed. We gain 20% in our MPG just by slowing down from 62 mph to 55 mph.
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Old 12-26-2013, 07:43 PM   #10
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If you live in CA. you can save about $200.00 (depending on the weight of your truck) a year by putting a topper on your truck and registering it as a "permeant mount". No topper, you are required to pay commercial weight fees, which for me amounts to $200.00 a year. I did not see a difference in the mileage per gallon after I put the topper on.
So what does "permeant mount" mean?
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Old 12-31-2013, 12:10 AM   #11
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So what does "permeant mount" mean?
In Ca. you are required to pay "weight fees" when you purchase a (new) truck. After one year, the truck may be registered as a "permanent mount" if a topper/camper shell is attached to the pick up bed. The term "permanent mount" means the topper/camper shell remains attached to the bed of the pick up truck (can not be removed) for registration purposes and the owner does not have to pay weight fees.
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Old 12-31-2013, 12:37 AM   #12
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In Ca. you are required to pay "weight fees" when you purchase a (new) truck. After one year, the truck may be registered as a "permanent mount" if a topper/camper shell is attached to the pick up bed. The term "permanent mount" means the topper/camper shell remains attached to the bed of the pick up truck (can not be removed) for registration purposes and the owner does not have to pay weight fees.
Another creative way to pick your wallet! Wow.....
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Old 12-31-2013, 07:25 AM   #13
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In Ca. you are required to pay "weight fees" when you purchase a (new) truck. After one year, the truck may be registered as a "permanent mount" if a topper/camper shell is attached to the pick up bed. The term "permanent mount" means the topper/camper shell remains attached to the bed of the pick up truck (can not be removed) for registration purposes and the owner does not have to pay weight fees.
So they TAX you for what your truck CAN carry - NOT what it's actual weight is, and figure that IF you mount a topper, you won't be carrying much extra weight in the bed on their roadways. Basically turning ALL trucks without a cap into WORK trucks weather or not they are, and then ALL trucks with a cap become SUVs.

Here in Florida, the DMV agents do not know the difference between CURB weight (actual weight) and GVWR (total you can carry per manufacturer) and will try to tax (tag fee) you on the GVWR. They tried to register my 1500 GMC as a HD truck the 1st time - about $30 more a year and renews in December. I had to carry in a weight scale ticket to them to prove it was a light truck! Now, with the 2500 Dodge, I have the heavy tag designation and have to keep it.
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Old 01-02-2014, 12:27 PM   #14
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So they TAX you for what your truck CAN carry - NOT what it's actual weight is, and figure that IF you mount a topper, you won't be carrying much extra weight in the bed on their roadways. Basically turning ALL trucks without a cap into WORK trucks weather or not they are, and then ALL trucks with a cap become SUVs.

Here in Florida, the DMV agents do not know the difference between CURB weight (actual weight) and GVWR (total you can carry per manufacturer) and will try to tax (tag fee) you on the GVWR. They tried to register my 1500 GMC as a HD truck the 1st time - about $30 more a year and renews in December. I had to carry in a weight scale ticket to them to prove it was a light truck! Now, with the 2500 Dodge, I have the heavy tag designation and have to keep it.
I think I have caused some confusion by saying "weight fees", sorry about that. When registering a pick up truck there is a weight fee added, the amount of the weight fee is based on the weight of the truck and you pay the weight fee every year you register the truck. The fee schedule is not weight specific, if your truck falls within a given weight range you pay the fee for that weight range, one pound over puts you into a higher weight fee bracket. When registering the truck new, DMV uses the manufactures curb weight, not the GVWR. Like you said it makes all pick up trucks commercial wether they are or not.

If your truck is used commercially, it does not matter if you have a topper on it or not, the weight fee is due.
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