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Old 03-12-2018, 02:36 PM   #15
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Ok, then at the end of the day, you need to look up the published gross pin weight rating of the truck you are using in your equation.

At that point, you can use the 20% rule of thumb (25% if you want to be super conservative), to determine max weight of trailer you can safely tow. Take that pin weight rating and divide by 20% (or 25%).


However, bear with me here: trucks also have a GCW (gross combined weight) that should not be exceeded. And that typically can be lower than just adding together the GVWR of the truck with the GVWR of the trailer.

My truck has a stated 23,500 GCW limit in a gooseneck or fifth wheel configuration.

My truck has an 11,400 GVWR and my 5er has a 16,750 GVWR. Combined that is 28,150, but on the scales, with all my gear, I am 22,800, with a pin of 2,940 (which happens to be 20% of my actual trailer weight). So I am comfortable with this combo.


So, I guess the moral of the story here is that there is not a simple formula.

If my trailer was fully and evenly loaded to 16,750, my combined weight would actually be 25,030, which would exceed its recommended GCW limit. Pin weight would also increase to 3,350, which is technically within limit on the pin.

If I loaded my trailer with lots of stuff in the front (unevenly) I could easily exceed pin weight AND GCW limit. A formula doesn't show you that.
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Old 03-12-2018, 02:56 PM   #16
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In your example of made up numbers yes you are correct.

as others have stated when the time comes the scale will be your friend and know that the published pin weights in the trailer spec sheet are generally wrong well they are based on a dry and unloaded trailer and does not include options either so they can be significantly different than the published weight when loaded and ready to go.

My trailer for example has a pin weight listed as 1525lbs (on a 10k trailer). Last trip through the scale on our way home showed it to be 1950 lbs. 425lbs or 28% over the published weight.
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Old 03-12-2018, 04:18 PM   #17
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Not neceesarily. You could be at or under the GVWR with your front axle under it's rating, but your rear axle is over it's rating.
So, are you saying that GVWR = FAWR + RAWR
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Old 03-12-2018, 04:36 PM   #18
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In your example of made up numbers yes you are correct.

as others have stated when the time comes the scale will be your friend and know that the published pin weights in the trailer spec sheet are generally wrong well they are based on a dry and unloaded trailer and does not include options either so they can be significantly different than the published weight when loaded and ready to go.

My trailer for example has a pin weight listed as 1525lbs (on a 10k trailer). Last trip through the scale on our way home showed it to be 1950 lbs. 425lbs or 28% over the published weight.
What I have learned is the GVW and GVWR are two different things regardless if you're talking about the tow vehicle or the trailer. GVW is the actual weight which will obviously vary as you place more (or less) weight in the vehicle / trailer. GVWR NEVER changes....it is the MAXIMUM weight limit that the vehicle / trailer is rated for...exceeding this limit means components could fail, control could be compromised, etc. etc. etc.
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Old 03-12-2018, 04:41 PM   #19
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A typical 5th wheel will have 90% of it's storage in the front. I load up the 'basement' storage with weed killer and bug killer, cleaning supplies, rake, shovel, pruning shears, awning shade and lots of other stuff. My wife loads up the under bed storage with sweeper, extra bedding, her cleaning supplies and lots of other stuff. All clothing is stored in the front. I have an added stacked washer/dryer in the front.

I weighed my rig at a Love's CAT scale and was ok with my loaded numbers because I am using a dually truck.

But do not under estimate the pin weight after you load the trailer with options and personal stuff.
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Old 03-12-2018, 08:05 PM   #20
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Payload is almost always your limiting factor. Payload includes anything or any one in the truck including fuel plus the pin/tongue weight of the trailer plus the w/d hitch or fifth wheel hitch weight. Lots of trucks have a really high tow capacity but the payload limit is exceeded long before that tow capacity is met.
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Old 03-12-2018, 09:34 PM   #21
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GAWR (front) + GAWR (rear) may be larger than GVWR. GVWR rules, do not exceed.

GCWR = trailer plus truck, do not exceed. However GVWR cannot be exceeded.

If you are at GVWR check the GAWR (front and rear). Neither can be exceeded, generally the rear will go over long before the front.

Unused GVWR can be moved to the trailer, not to exceed GCWR, however unused GCWR cannot be added to GVWR.

In essence there are a number of formulas that have limits based on other limits. In all cases the lowest is the one to use.
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Old 03-12-2018, 10:39 PM   #22
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I'm just asking if the equation is correct or incorrect. I like to understand how to derive these things and understand the relationships. I'm not much one for trusting calculators, website tables. If you don't understand, then you never know if the answer is correct. I do trust the manufacturer's published specs.
Gordon did a fine job in the previous post.

I'll mention that the trouble with the published specs is that... they are base numbers. Each individual truck will have its own payload adjusted based on options or trim packages selected from the factory. The same is often true for trailers. Good as a baseline, just be careful with those numbers.

Here is a good video explaining... https://youtu.be/I6RIJrwu9AM?t=42s
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Old 03-13-2018, 12:41 AM   #23
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All the “Rs”, as in GVWR, GAWR & GCWR are based on regulatory safety factors and each acronym stands on it’s own “R” value.

The GVWR is the primary “R”. Once certified on the vehicle’s certification label it cannot be safely exceeded nor is it recommended to be exceeded. Unless, it’s modified. Only it’s manufacturer or a certified vehicle modifier has the authority to change certified GVWR values.

The GAWR is a rating strictly for the axles on your vehicle. They may differ in the way they are fitted by the vehicle manufacturer.

Motorized vehicles almost always have GAWR values that total out higher than the vehicle’s GVWR. That’s because the vehicle manufacturer is using them and the tires fitted to them to provide the vehicle with load capacity reserves. They will tell you right in the owner’s manual not to exceed GVWR.

For trailer service the axles may have two distinct GAWR values. One is the actual certified GAWR assigned by the axle manufacturer and displayed on each individual axle. The other is a certified GAWR value assigned to that axle by the vehicle manufacturer for fitment and vehicle certification purposes. Therefore, the GAWR values found on the trailer’s certification label are the official values to be used for that vehicle fitment.

The “R” in the GCWR can be a verbal value. For instance, my older Dodge Dually Cummins Diesel has a GVWR of 11500# and it’s stock GCWR was 22500#. However, with an optional 4.10 gearing the GCWR was increased to 23500#.

Note: Our truck fully loaded for the road had a GVW of 8700#, fiver hitch avg 2700#, combined load avg 23000#.
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Old 03-13-2018, 07:37 AM   #24
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So, are you saying that GVWR = FAWR + RAWR
No, that's not what I'm saying. What I am saying is that it is possible to be at or under the GVWR, but an axle might be over its GAWR.
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Old 03-13-2018, 10:24 AM   #25
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Thanks, Thanks, Thanks, and Thanks....all great and very helpful. I'm just stuck on one part of this now. How do you scale / weight your actual Axle Wt. (Front or Rear)???
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Old 03-13-2018, 10:30 AM   #26
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Thanks, Thanks, Thanks, and Thanks....all great and very helpful. I'm just stuck on one part of this now. How do you scale / weight your actual Axle Wt. (Front or Rear)???
Take it to a CAT scale. Your local truck stop likely has one.
It's the only way to know for sure once it's all fully loaded. However at the point you've already purchased the trailer.
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Old 03-13-2018, 10:33 AM   #27
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Take it to a CAT scale. Your local truck stop likely has one.
It's the only way to know for sure once it's all fully loaded. However at the point you've already purchased the trailer.
There are explanations and how to do it charts in chapter four of the following ref.

https://www.ustires.org/sites/defaul...TruckTires.pdf
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Old 03-13-2018, 08:55 PM   #28
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No, that's not what I'm saying. What I am saying is that it is possible to be at or under the GVWR, but an axle might be over its GAWR.
True with todays high GVWR trucks (some.... not all). Just another fallacy of using a gvwr number/payload number to determine how much payload the truck can carry in the bed.
Example is a late model 2500 GM 6.0 gas double cab and 6200 rawr has a 3640 lb payload sticker. These trucks can weigh 3000 lbs on the rear axle....now add 3640 lb payload in the bed = 6640 lbs for a big 440 lb overload.

Any load carrying equation will have to factor in the trucks fawr/rawr especially rawr as its going to carry all the hitch load and other gear in the bed.

A 14xxx lb 5th wheel/GN trailer can have a 20-22 percent pin weight = around 3000 lbs which puts the truck in the one ton SRW class at a minimum.
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