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Old 12-10-2010, 08:06 PM   #1
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GVWR < front GAWR + rear GAWR ?

I was going over the specs for my tow vehicle and noticed some inconsistancies which I hope someone can explain. First, I noticed that the GVWR was significantly less than the combine GAWR:

GVWR = 9000
front GAWR = 5200
rear GAWR = 6010

Although the difference between the GVWR and the front and rear base weights does equal the payload capacity:

front base weight = 4487
rear base weight = 2680
total base weight = 7167
payload capacity = 1830 (9000 - 7167)

The theoretical carrying capacity based on the GAWR's is significantly higher:

theoretical front payload capacity = 713 (5200 - 4487)
theoretical rear payload capacity = 3330 (6010 - 2680)
total theoretical payload = 4043

This is more than twice the listed payload capacity.

What am I missing?
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Old 12-10-2010, 10:47 PM   #2
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What do you have going here, a 3/4 ton, 4wd, diesel crew cab something or other, fully loaded with options?

We need to know the source of all your numbers. Typically base weight numbers are just that, a base work truck regular cab regular bed 2 wd w/o any options. Anything you add to those numbers increases the base weight of your particular truck and takes away from payload. GVWR remains the same.
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Old 12-10-2010, 10:53 PM   #3
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I should say, "increases the curb weight of your particular truck..."
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Old 12-10-2010, 11:41 PM   #4
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Quote:
Originally Posted by dznf0g View Post
What do you have going here, a 3/4 ton, 4wd, diesel crew cab something or other, fully loaded with options?

We need to know the source of all your numbers. Typically base weight numbers are just that, a base work truck regular cab regular bed 2 wd w/o any options. Anything you add to those numbers increases the base weight of your particular truck and takes away from payload. GVWR remains the same.
You are correct. I have a 2008 diesel Dodge Ram 2500 Quad Cab with an automatic and a long box. The numbers are from the 'Body Builders Guide' on the Dodge website:

https://www.dodge.com/hostb/crossbrand/owners/en/

The actual weights for the front and rear axle are 4740 (front) and 3580 (rear). These weights include the driver, a canopy, dog crates, retriever training equipment and 3 dogs. In other words, everything that I will be hauling with the exception of the trailer, hitch and generator. Based on the GVWR I can only carry an additional 680 lbs but I am still well under the front and rear GAWRs.
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Old 12-10-2010, 11:55 PM   #5
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OK, you can throw base weights out of your mind. Your curb weight is whatever the new truck was full of fluids and 1 - 175# (I think) occupant. You added quad cab, diesel, long box and any other non-standard options from a base 2500 work truck. Now add all your stuff...dogs, etc. By the numbers, you're kinda screwed after you hitch up.

However!!! If you're under on GAWRs and GCWR and only marginally over on GVWR, you may be ok. Try shifting some gear to the trailer if you have excess GCWR and trailer GVWR. OR!!! if you're only a little bit marginally over GVWR on the truck and everything else is OK....well...maybe go with it.

BUT, please don't forget to revisit all the numbers at the scales, hitched up and ready to go. Adjust load accordingly. MOST IMPORTANTLY, have fun and be SAFE!
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Old 12-11-2010, 12:01 AM   #6
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This is very common. The overall weight carrying capacity is determined by a number of factors, including radiator capacity, brakes, legal fictions, etc. The axles and suspension have ample capacity to provide flexibility in loading.

My diesel 4x4 crewcab has a GVWR of 8800 lbs (it's a 3/4 ton), but the rear axle has a load rating of 6000+ lbs and the front of 4000+ lbs.


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Old 12-11-2010, 12:25 AM   #7
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Originally Posted by dznf0g View Post
OK, you can throw base weights out of your mind. Your curb weight is whatever the new truck was full of fluids and 1 - 175# (I think) occupant. You added quad cab, diesel, long box and any other non-standard options from a base 2500 work truck. Now add all your stuff...dogs, etc. By the numbers, you're kinda screwed after you hitch up.

However!!! If you're under on GAWRs and GCWR and only marginally over on GVWR, you may be ok. Try shifting some gear to the trailer if you have excess GCWR and trailer GVWR. OR!!! if you're only a little bit marginally over GVWR on the truck and everything else is OK....well...maybe go with it.

BUT, please don't forget to revisit all the numbers at the scales, hitched up and ready to go. Adjust load accordingly. MOST IMPORTANTLY, have fun and be SAFE!
I forgot to mention it is also a 4X4.

Theoretically, I will be right at the GVWR when the weight ditribution hitch is set correctly. According to the Airstream Owners Manual, the correct setting for the weight distribution hitch will transfer 1/3 of the tongue weight back to the trailer axle and 2/3 of the tongue weight to the truck axles.

I will still be away under the rear GAWR (the front will be close to but still under the front GAWR). Even though I am at the GVWR, the rear axle can theoreticall still carry almost 2000 lbs. This is what I do not understand.
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Old 12-11-2010, 12:40 AM   #8
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Originally Posted by PJohnson View Post
I forgot to mention it is also a 4X4.

Theoretically, I will be right at the GVWR when the weight ditribution hitch is set correctly. According to the Airstream Owners Manual, the correct setting for the weight distribution hitch will transfer 1/3 of the tongue weight back to the trailer axle and 2/3 of the tongue weight to the truck axles.

I will still be away under the rear GAWR (the front will be close to but still under the front GAWR). Even though I am at the GVWR, the rear axle can theoreticall still carry almost 2000 lbs. This is what I do not understand.
Realistically, I think you'll see less than 1/3 on the trailer, less than 1/3 on the front, and more than 1/3 on the rear. And that's fine, as long as the front is close to the unhitched weight and you're under on GRAWR.

Ok, here's the best way to look at it, GVWR and GAWRs are vertical limits. That is the truck's backbone (frame), springs, axles, wheels and tires ability to bear a vertical load, individually as well as collectively.

GCWR is the truck's ability to haul a horizontal load, (GVWR is only a fraction of the truck's ability to move mass) and is typically limited by powertrain, cooling system, and braking ability. (ie. going and stopping ability) That's simplistic, and obviously there's some overlap in demand on each part of the system, but it's pretty accurate.
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