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Old 03-27-2011, 07:36 PM   #11
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Ok, I'm real new also, and I have learned alot from the helpfull guys on here.
So, you have come to the right place for guidance!!!!!
I also was told faulty information about towing stats etc. from trailer and auto dealers.
But I guess if I always remembered the addage "mediocrity cuts across all professions" I wouldn't have been so surprised by it.
This is my understanding about trailer ratings as learned from this forum and my good friend Google.

To determine what your truck can handle, first you need to know what the Trucks GVWR is, and from there determine what your payload capacity is.
So lets try this and fill in the blanks with your numbers.

(GVWR of Truck) 7150lbs - Curb weight = _______lbs of payload
_______lbs of Payload - Passengers - Cargo - Tongue Weight = _______lbs
This last number must be higher than 0 if it isn't you are over the GVWR of the truck, and you better look at a different trailer.
If you are all good here, let's move on.
GCVWR = 13,000lbs
13,000lbs - 7730 (GVWR of Trailer) = 5270lbs Truck weight (which is too high)

If you take your 13,000lbs and subtract the number that you calculated on the 2nd line, that to me would be a more correct GVWR of a possible trailer (factoring in a lower tongue weight of course)

Please correct me if I'm wrong
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Old 03-27-2011, 08:17 PM   #12
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Go to website (Changears.com) you supply the INFO and they tell you,No guessing! Youroo!!
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Old 03-27-2011, 08:56 PM   #13
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Could not find changears.com website typed in and googled nothing came up?
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Old 03-27-2011, 09:35 PM   #14
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he must have meant changingears.com

Travel Trailer Weight Calculator
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Old 03-28-2011, 06:40 AM   #15
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he must have meant changingears.com

Travel Trailer Weight Calculator
Yes thats it, Thanks. Youroo!!
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Old 03-28-2011, 06:59 AM   #16
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Go have your truck weighed to see the REALLY weight loaded (gas too)...13k is NOT what a F150 can haul... I have one! Also depends on the accessories too... is it a 4 door? Do you have a bigger/ heavier rear axle? Truck manufactures tend to over estimate their towing capacity.
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Old 03-28-2011, 09:00 AM   #17
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Originally Posted by campnqueen View Post
Truck manufactures tend to over estimate their towing capacity.
Ain't that the truth! And google isn't helpful on this subject as you'll always find the max tow rating a vehicle can handle under ideal conditions/options.

The difference between ideal and reality on my expedition is 1500 lbs. Things I didn't find on the net that are in the owners manual that affect tow rating are rim/tire size. Bigger rims lower the tow rating (cause the lower the load rating). 4x4 will lower tow rating (more weight on tow vehicle), options as mentioned affect it, and then there's the little paragraph that says "trailer frontal area not to exceed 60 sf"

Since the expy is F150 based i'd imagine it's about the same for you truck.

13,000 - truck wt empty (5400?) leaves 7600. Add in cargo (people, pets, gas, firewood, HITCH, etc) - 800lbs? That comes off the 7600 leaving 6800 lbs for the trailer and everything you put in the trailer.
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Old 03-28-2011, 09:10 AM   #18
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Pro fate - "trailer frontal area not to exceed 60 sf"? is this for a fifth wheel? I am just guessing....Never heard this term before.
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Old 03-28-2011, 10:54 AM   #19
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Pro fate - "trailer frontal area not to exceed 60 sf"? is this for a fifth wheel? I am just guessing....Never heard this term before.
Thats in the book for the expedition, an SUV so it can't be for a fifth wheel. Makes sense regarding wind resistance on the highway though.

I've not measured the frontal area of any trailer, but if it's 8' wide and 8' tall that's 64 sf... now the grey wolf we bought has a very sloped front of the hard plastic material so it will be more slippery than most other designs.
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Old 03-28-2011, 11:08 AM   #20
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I found this article regarding DRAG index

This article regards how drag is computed based on shape, speed, and area presented to the wind. It is pretty complete but the example is F-16 external stores (which vary from sleek fuel tanks to "dirty" munition shapes).

**************************************************

Drag index of a store is a shorthand way of estimating the drag of a store at a typical cruise mach number. The basic airplane has a drag index, and each piece of added equipment (pylons, tanks, bombs, pods, etc) had a drag index. When all the drag indexes (indicies??) are added, the complete configuration drag index is found.

The drag on a body is drag coefficient x dynamic pressure x reference area, or D = Cd x q X S. To get the total configuration drag, you could look up the Cd for each item (store, pylon, pod, basic airplane), look up the reference area for each item, calculate the drag on each item, than add all the drags together. A simpler way is to use the same reference area for all elements, add all the coefficients (drag indexes) together, and calculate the total drag.

There should be a list of store drag indexes somewhere in the stores TOs, but if you can't find it or if the store isn't listed, all is not lost.

A drag index for a clean F-16 is the drag coefficient at 0.8 mach using the reference area of the F-16 (300 sq. ft.). So what is a drag coefficient? Using a clean F-16 as an example, say the drag at 0.8 mach, sea level, is 8000 pounds.

D = Cd x q x S

so Cd = D / qS

D = 8000 lb
q at .8 sea level is 947 lb/ sq ft
S = 300 sq ft

so Cd = 0.0282

The basic airplane drag index would be 282, because it is more convenient to use whole numbers instead of all those decimal places.

To calculate a drag index for a store, first you have to find its drag coefficient based on it's cross section area. That information (Cd) may be difficult to find, but the manufacturer should be able to give it to you. If that fails, then use 0.15 for pointy store (Mk-82) or .20 for a blunt store (AGM-65) as a good estimate for Cd. Then calculate the Cd based on the F-16 reference area, 300 sq ft.

Cd (F-16 ref area) = Cd x (store cross section area / 300 sq ft). This value, after removing the 4 decimal places, is the store drag index.

Another way to estimate a store drag index is to find another store of similar shape, and use its drag index multiplied by the ratio of the store cross section areas. For example a Mk-84 and a Mk-82 have similar shapes. If you know the -84 drag index, (DI-84), you can estimate the DI-82 :

DI(82) = DI(84) x Area (82) / Area (84)

I apologize if I've gone into more detail than you wanted.

*************************

So if you made it this far; drag must be overcome with engine power delivered to the drive wheels, so fuel economy and towing performance is based on:

Pointy is good; blunt is bad
Slow is good; fast is bad
Smaller cross section is good; tall and wide is bad
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