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Old 08-15-2012, 03:33 PM   #21
datedd
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Quote:
Originally Posted by therink View Post
Tow rating is one thing, gross combination weight rating is another. It is gross vehicle weight rating of the tow vehicle that is the largest factor, especially with 5th wheels.
This means that the true weight of the truck including optional equipment, hitch, cargo and passengers plus loaded pin and/or tongue weight of trailer can not exceed the GVWR of the truck.
The weight from the hitch or pin usually maxrs out the gvwr of the truck long before the tow rating of the truck is exceeded.
A lot of people ignore this factor, hence they are overloadingthe axle capacity of their truck.
What is the difference when considering axle rating vs payload or vice versa? Say a truck with a RGAR of 7000# and it's payload capacity is about 4000# (GMC Sierra 3500 HD SRW).

Is not the pin's forces concentrated down to the axle thus the axle shouldering the load? Where does payload come into play here?
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Old 08-16-2012, 06:47 AM   #22
Jim W
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My disclaimer; I am not a member of the weight police nor will I enforce the weight police policy’s.

I do not concern myself with payload when towing my 5er. To me payload is what the tuck can carry if it is not towing a TT or 5er. Payload is the mass that is placed in the bed such as gravel, sand, bricks and other material; this is why a weight number is provided by the vehicle manufactures.

Now I do check to insure that I do not exceeded the Gross Vehicle Weight, the Gross Combined Vehicle Weight, the Front Axle Gross Weight and the Rear Axle Gross Weight when pulling any TT or 5er. And I do not exceed these number with my 11,5K 5er a cougar 318 SAB and ¾ ton truck.

My example will use a 5er since a TT will use a different approach. If you look at a free body diagram of the mass that is distributed over the hitch this mass has a forced that is distributed in portion to the distance away from the pin to the frame over four points. This is in turn transferred to the frame and axles with most of the mass if not all over the rear axle. This mass is split equally over the rear tires and wheels which really end up supporting the entire mass of the trailer that is placed on this said vehicle.

So if you have a RAGW of 7000 LBS than the axle cannot support any more than this load as certified by the vehicle manufacture. Which you should be able to pull most medium size trailers say up to 12,000 to 13,000 LBS with. This will depend on the pin weight or hitch weight of said trailer along with what every else is carried in the cab and bed of the truck.

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Old 08-16-2012, 02:00 PM   #23
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Thank you Jim, that gives me something to think about.
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