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Old 05-14-2013, 07:23 AM   #1
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Weights & Capacities – Clarification

First, let me say that I have vigorously perused the various threads here and in other forums, trying to get a mental grip on how to apply the concepts to real world situations. I post this missive here as, frankly, this forum seems to have the most knowledgeable ‘denizens’ that don’t (usually) get into name calling contests.

Next, yes, I know I need to get to a CAT scale for verification – It’s on the ‘to-do ASAP’ list.

Also, please notice all the qualifier (weasel) words throughout. This entire post is hypothetical and is based on the idea of better understanding the concepts required to apply the required calculations to real world situations as they arise.

Finally, please note that I have left out tire capacities as that is another discussion that has (IMO) too many nuances to try to get into here.

All this said let me walk through this to see if I have decent understanding of these basic concepts.

GVWR (Gross Vehicle Weight Rating) – is the maximum weight that the vehicle can safely weigh when fully loaded, including (as applicable) fuel, passengers, water (fresh, grey and black), food, furnishings, electronics, clothing, tools, batteries & solar panels and et cetera.

For a tow vehicle, this means the weight of the fully loaded and fueled vehicle, weighed on a scale, subtracted from the labeled weight (usually) on the driver door pillar.

In my case, the GVWR of my F350 (SRW) of 11,200 minus the (published specification) weight of 6,250 gives a (calculated) payload capacity of 4,950 pounds. The published specification says the payload capacity is 4,400 pounds – so there’s some discrepancy between the numbers in the Ford published specs.

We know this is not a real world number so let’s add 1,450 pounds of weight for a (still estimated) closer to reality weight of 7,700 pounds. (Yeah, it may weigh more in reality, but for the purposes of this missive, it's good enough). This number then derives a payload capacity of 3,500 pounds. IMO this is a much more ‘reasonable’ number for a 1-ton pickup. Yes, I know I need to get to a scale for verification.

For a trailer, the weight of the fully loaded and watered vehicle, weighed on a scale, cannot exceed the sticker GVWR.

The NCC (Net Carrying Capacity) of the trailer is its true unloaded weight – weighed on a scale, when the water tanks (fresh, grey and black) are empty, no food, furnishings, electronics, clothing, tools, batteries & solar panels and et cetera are aboard the vehicle – subtracted from the stickered GVWR.

GCWR (Gross Combined Weight Rating) – is the maximum weight that a tow vehicle can safely travel on a highway. GCWR includes the fully loaded tow vehicle and fully loaded trailer.

Now we get to axle ratings.

For my F350, the sticker says that the rear GAWR (Gross Axle Weight Rating) is 6,830 pounds with LT275/65R18 tires on 18X8.0J rims inflated to 80 PSI.

The front GAWR is 4,850 pounds with the same tires and rims but inflated to just 60 PSI.

Let’s see if we can assemble all the data and ratings into a comprehensible whole.

So… In my case, the published towing specifications for my F350 tell me that I cannot exceed a GCWR of 23,000 pounds. The door pillar sticker says 11,200 pounds for a GVWR and 6,830 pounds for the rear GAWR.

Hypothetically, if we allow for the estimated weight of the fully fueled and loaded PU at 7,700 pounds, that means that the theoretical maximum trailer weight can be 15,300 pounds and still not exceed the published GCWR.

But… the calculated pin weight of this 15,300-pound trailer will be between 3,060 (20%) and 3,850 (25%) pounds. So this means that in this hypothetical example we will be safely under the PU GVWR at 20% and slightly over at 25%.

If my understanding is correct, we cannot calculate the weight distribution for the axle loading. With a SWAG (Scientific Wild Ass Guess) we can postulate that the rear axle will be overloaded at the 25% pin weight – probably by a significant amount. And may be overloaded at 20%, but we would need to verify this on a CAT scale.

Most likely the reality is that I cannot safely tow a trailer with my SRW F350 that weighs anywhere close to 15,000 pounds.


Working backwards, it seems that any trailer that stays under a GVWR of 13,000 (25% pin weight = 3,250 pounds) will likely be within the capacity of the F350, including staying under the GAWRs.

Working further backwards, this means that (depending on brand and model) I must look a trailer with a published empty weight of 9,500 to 10,500 pounds as a maximum. The (hypothetical) NCC will be in the area of 2,500 to 3,000 pounds.

Working further backwards, this means (depending on brand and model) the trailer cannot be longer than 32 to 34 feet. Longer trailers (generally) weigh more than I can safely (and legally) tow with my F350.

Again, all this is hypothetical and is presented here to help me verify my understanding of the concepts and application to ensure that I tow both safely and within legal limits.

Please pick me apart wherever I’ve screwed up – please help me understand.

Thanks!
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Old 05-14-2013, 12:23 PM   #2
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I think you're on the right track, but you're over-complicating it.

For a late-model F-350 SRW, your limiter will be GVWR minus actual weight of the wet and loaded truck, which gives you max hitch weight. For almost all fifth-wheel RV trailers around 12,000 to 13,000 pounds GVWR, the hitch weight is going to be 18% to 20% of wet and loaded trailer weight. If you use 20% for your SWAGs, then you'll probably be fine when on the road with the wet and loaded RV crossing your first CAT scale. Ignore axle weigh limits, tire weigh limits, GCWR and tow rating, and every other weight rating except GVWR. If you don't exceed the GVWR, then you won't exceed any other weight rating.

You estimate of 7,700 pounds truck weight is a bit low, per my experience. My '99.5 CrewCab 4x2 diesel with me, DW, puppydog, 5er hitch and some tools weighed about 8,000 pounds before we tied onto the trailer. Newer Superduties are heavier, and add about 400 pounds if yours is a 4x4. But with 11,200 GVWR, you must have the gas engine, so that reduces the weight by a few hundred pounds But 8,000 would probably be a better estimate than 7,700.

So 12,000-pound trailer with 2400 pounds hitch weight leaves you 8,800 pounds for max wet and loaded weight of your F-350. I wouldn't want to take a chance on any heavier trailer until I had some good CAT scale reports. So with your truck, I'd limit my search for a 5er to those with GVWR less than 12,000 pounds.

Here's the simple math:

F-350 SRW with GVWR 11,200
12k 5er with 2,400 pounds pin weight
8,800 pounds max wet and loaded truck weight.

That's a nice cushion if your DW doesn't decide to bring back several hundred pounds of pretty rocks from the tulllies. (Yes, you need that cushion.)
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Old 05-15-2013, 12:22 AM   #3
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Get a trailer in the mid 30's length that grosses at 14,000 and you'll be fine. Theres plenty to choose from. The F350 SWR are usually rated for a 15900 or so 5er. Check your owners manual to be sure.
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Old 05-15-2013, 09:09 AM   #4
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azdryheat,
You can't go by length, different trailers of the same length have different GVW's. An example is my 5er is 30' and has a GVW of 16,400#, so no way would it fit within the limits of a SWR truck.You must go by the GVW of the trailer and forget about the length for this calculation. LeoinSA, you have a pretty good understanding of what you need to look for. Now you need to make a trip to the CAT scales to verify your truck weight.
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Old 05-15-2013, 09:19 AM   #5
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Did you say what year or engine or cab configuration you had ?
even though it's a "hypothetical exercise"
as Smokey stated, sure you know an 350 can weigh more than your number...

here's the 2013's 2013 Ford Super Duty | Detailed Chassis Specifications | Ford.com

and even those charts are just a guide as I learned the hard and expensive way

but good on you for trying to understand the calculus before it's needed !!! good luck !
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Old 05-15-2013, 12:49 PM   #6
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Thanks for all the comments. Appreciate them.

I'll get to a scale ASAP.

I know I went about this bass-ackwards - but limited budgets and good deals have a way of focusing and changing plans.

I've just bought a 2006 F350 SRW crew cab XLT with the 6.0l diesel. It's the 'basic' XLT without lots of doo-dads and gee-gaws. 1 owner with 111,000 miles. Factory tow package, but never had a hitch bolted into the bed.

Please do not jump my azz about the 6l engine. I've read the good and bad and most of the bad was for the earlier years - although 'some' are bad in the later years too. We'll just hope & pray that this is one of the good ones when I start towing.

Specs for this particular truck are 11,200 GVWR - 23,500 GCWR.

Most trailers I've looked at that I can afford are older units that are under 32-33 feet have their GVWR near 15,000.

I'm becoming more and more surprised at how close many trailer manufacturers run close to that number with an empty weight, leaving (after water and propane) a paltry 1200-1600 pound of cargo carrying capacity. What were they thinking? Especially for rigs that are supposed to be suitable for extended living. Silly twits.

The search for a good clean used trailer goes on. There are candidates all over the nation - but at an average of 14 MPG (Fuelly) I'm not going to traipse all over hoping to find the right one. It'll have to be nearby and pretty special. But, part of the fun (at least for me) is finding that special deal that doesn't cost an arm and a leg.

Again, thanks.
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Old 05-15-2013, 01:46 PM   #7
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If your head hurts , and you've killed a set of calculator batteries, your getting close.
At least you know there are limits to what you can safely tow, and that's 1/2 the battle.
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Old 05-15-2013, 09:53 PM   #8
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Quote:
Originally Posted by LeoinSA View Post
Thanks for all the comments. Appreciate them.

I'll get to a scale ASAP.

I know I went about this bass-ackwards - but limited budgets and good deals have a way of focusing and changing plans.

I've just bought a 2006 F350 SRW crew cab XLT with the 6.0l diesel. It's the 'basic' XLT without lots of doo-dads and gee-gaws. 1 owner with 111,000 miles. Factory tow package, but never had a hitch bolted into the bed.

Please do not jump my azz about the 6l engine. I've read the good and bad and most of the bad was for the earlier years - although 'some' are bad in the later years too. We'll just hope & pray that this is one of the good ones when I start towing.

Specs for this particular truck are 11,200 GVWR - 23,500 GCWR.

Most trailers I've looked at that I can afford are older units that are under 32-33 feet have their GVWR near 15,000.

I'm becoming more and more surprised at how close many trailer manufacturers run close to that number with an empty weight, leaving (after water and propane) a paltry 1200-1600 pound of cargo carrying capacity. What were they thinking? Especially for rigs that are supposed to be suitable for extended living. Silly twits.

The search for a good clean used trailer goes on. There are candidates all over the nation - but at an average of 14 MPG (Fuelly) I'm not going to traipse all over hoping to find the right one. It'll have to be nearby and pretty special. But, part of the fun (at least for me) is finding that special deal that doesn't cost an arm and a leg.

Again, thanks.
I have a 2005 F250 with 18"wheels and added spring ply and the truck pulls a 09 big country by Hartland very well. Its the lightest of the full timer unts with 500 lbs less on the pin and 1000 less GVWR with same frame and axles. So less heavy options. We love it and the 7k axles are just what I was looking for. The aero and tire drag is very small for the size of the unit. Towing is a breeze. But stock power makes the unit feel heavy. My Hypertech set at level 2 takes the trailer weight off.
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Old 05-16-2013, 10:22 AM   #9
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You will hear some say not to go by the stickered weights on a trailer. Our recently acquired 2013 TT and '09 F250 had some surprises after going to the CAT scale and an actual real life experience is below.

Our trailer is 29'. The UVW is 5,480 lbs and the CCC is 1,320 lbs. And the NCC on the sticker with tire info says 1,563 lbs. Woohoo, sounds great so far! The GVWR is 6,800 and the axles are 2 x 3500 lbs. But the scale shows the wet/loaded weight to be 6,450 lbs. We didn't really have much cargo inside the trailer other than about 1/2 the amount of food we'd have on a longer trip and some clothes. We sure didn't to load anything near the CCC or NCC. It seems to me that the factory does not include factory added options like power awning and elec. stab. jacks in the UVW since the figure on our sticker is close to the figure published in their literature. Even if you consider the weight of propane tanks and battery, it's still a lot less than you'd think. If we travelled with a full tank of fresh water, we could easily be at or over the TT GVWR. We only have one battery as well. We now need to be aware about the trailer weight not to overload it and exceed the GVWR and axle ratings - there just is not much of a comfort margin. (If your frame cracks some day, you sure don't want the manufacturer blaming you for overloading.)

With our truck, it has a max. payload on the door jamb sticker of 2,850 lbs. Yeehaw, sounds really good! But the scale shows the actual max. payload to be 1,820 lbs. Bummer. That's a LOT less than the sticker amount. (No problem with axle ratings, tires or hitch tho.) That kind of difference could have a huge impact for some folks. Fortunately, we're under the GVWR normally, but if we had 3 heavy passengers in the back seat and some heavy stuff in the bed, we could be near or even over the GVWR. So much for having a 3/4 ton truck! Also, interestingly, our hitch is rated for 1,250 lbs tongue weight and we can pull max. 12,500, but if we had a TT near 12,500 loaded and a tongue weight of 13%, we'd be well over the factory hitch capacity.

It's good for someone to do research on weights in advance of making a purchase decision. It seems clear to me now that you just cannot go by the stickered or advertised weights of a trailer and even the TV. It seems like in most cases, the GVWR of the TV and scaled weight will be the deciding factor. And it seems that it can be easy to load a trailer to the GVWR quite easily. Moral is - it's all in the actual numbers so get your TV and TT or 5-er to a scale!
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Old 05-16-2013, 02:52 PM   #10
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(If your frame cracks some day, you sure don't want the manufacturer blaming you for overloading.)

If it cracks, they'll blame you anyway...

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Old 05-18-2013, 04:39 AM   #11
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I payed for cat scale once 20 years ago and the weight results were so far off that I just scraped the results and never returned. I will go by manufacture shipping weight and 1000 lbs of added stuff plus gallons of water on board.
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Old 05-18-2013, 05:32 AM   #12
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There are other scales available, so IF the set you used were off, that doesn't preclude using another set of scales. If you used actual CAT scales, here's their guarantee:

Quote:
CAT Scale Offers an Unconditional Guarantee

If you get an overweight fine from the state after our scale showed you legal, we will immediately check our scale. If our scale is wrong, we will reimburse you for the fine. If our scale is correct, a representative of CAT Scale Company will appear in court with the driver as a witness.

It’s that simple, and just another reason why we are your #1 choice.

We guarantee it all! That’s right! We guarantee axle weights to be accurate as well as the gross weight.
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Old 05-18-2013, 06:17 AM   #13
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I payed for cat scale once 20 years ago and the weight results were so far off that I just scraped the results and never returned. I will go by manufacture shipping weight and 1000 lbs of added stuff plus gallons of water on board.
Isn't this kinda like "I can't possibly be that fat, therefore the bathroom scale is wrong!"
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Old 05-18-2013, 07:36 AM   #14
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Yep, head in the sand syndrome...

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