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Open Roads Forum  >  Beginning RVing

 > Moving up to a Ram 2500.. but have some weight questions..

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audiodane

alabama

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Posted: 05/02/19 01:37pm Link  |  Quote  |  Print  |  Notify Moderator

Hello again,

I'm an engineer and I like equations that balance. But I am up against two differing sets of equations that are NOT matching. I was hoping to get some feedback here...

summary
After renting and borrowing several travel trailers with our 2014 Expedition EL (w/ HD Tow Pkg), we are now in the process of moving up to a RAM HD truck. Currently looking at the 2014+ RAM 2500. We don't want a dually, and we have a family of five. We're looking at a 2500 Crew Cab. The 3500 SRW increases payload but not much more. But it's payload on the 2500 that I'm concerned about. I have read so many posts, and talked to so many people, about pin weights, pin weight ratios, axle ratings, etc, that my head is spinning. Some say ALL my numbers need to be in-spec. Others say axle ratings and gcwr are what matters and tow vehicle gvw's are simply for class categorization of a vehicle.

But -- let's go through a specific example:

truck: 2014 Ram 2500 CTD 4dr 4x4 SRW Long Bed 3.42 (using this fantastic post!)

5th wheel: Highland Ridge LF295FBH (Mfgr Website)

kingpin weight ratios
I hear folks say 20-25% trailer UVW, some say 20-25% trailer GVW. However manufacturers ratings go as low as 15% UVW on their spec sheets! In the RV above, the mfgr shows a 1,351lb hitch weight which is only 15% of UVW's 8,995lb ...

  • Question: Is the mfgr being misleading, or is this RV "designed" to be pulled with a 15% kingpin hitch ratio?


gvwr/payload vs axle ratings
From what I can find, the axle ratings generally seem to add up to more than the gvwr. The vehicle listed above has a gvwr of 10,000lbs but a combined axle rating of 12,500lbs. Payload is calculated by gvwr - curb weight, which equals 2,180lb; but if you calculate payload as axle rating - curb weight, you more than double to a whopping 4,680lbs!

  • Question: Why do the combined axle ratings so often *exceed* the tow vehicle's gvw?


calculation differences
payload vs axle ratings makes a huge difference in kingpin weight ratios, using the examples above. With the two calculation methods described above, there are two possible outcomes. But first some assumptions:

gcwr is totally fine: tv curb weight (7,818) + rv gvwr (10,995) = 18,813.... WAY under the tow vehicle's gcwr of 25,000; Also, rv gvwr (10,995) is also way under tow vehicle's max tow capacity (17,010).

family+in-cab stuffs: 600lb for axle calculations, or 450lb (600-150) for payload calculations (b/c http://www.rambodybuilder.com specifically says the 2014 Ram 2500 payload number includes a 150lb driver)

5th wheel hitch: ~150lb

using payload method: 2,180 - 450 - 150 = 1580lb
using axle rating method: 4,680 - 600 - 150 = 3930lb

Wow! That's a huge difference!

trying to close the loop
Using the payload method, I can only tow the highland 295FBH with between a 14-17% kingpin weight ratio (14% of gvwr, around 17% of uvw). However, if I use the axle rating method, I can easily tow it *fully loaded* (10,995lb) with a 25% kingpin weight ratio (2750lb) and still have another 1,180lb of safety margin!

This is a HUGE difference. And there are plenty more RV's that fit into this scenario with something like a 2014 RAM 2500.

  • Question: Before I purchase the truck, how do I reconcile these two vastly different outcomes?


..dane

EDIT: fixed rv link

* This post was edited 05/05/19 10:54pm by audiodane *


2018 Ram 3500 CC SB 4x4 SRW

audiodane

alabama

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Posted: 05/02/19 02:00pm Link  |  Quote  |  Print  |  Notify Moderator

One quick add of confusion...

We were at a RAM dealership yesterday, and the guy gave me a "Ram Job-Rating Worksheet" (2016 version) which clearly states 15% kingpin weight for for fifth-wheel trailer. Yay!! However, when searching online for it, I came up with an older version (from 2010) that states 25% kingpin weight ratio. Ugh!!

EDIT: If I can figure out how to attach images or PDFs here, I can post both files

Second Chance

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Posted: 05/02/19 02:57pm Link  |  Quote  |  Print  |  Notify Moderator

Use 23% of a fifth wheel's GVWR to estimate loaded pin weight. If you have a family and are planning on a fifth wheel and carrying everyone in a crew cab, forget any 3/4-ton truck and go straight for a 1-ton SRW minimum. There are lots of folks out there who are members of the "Two-Timers' Club" - those who didn't buy enough truck the first time around and had to eat the depreciation and upgrade.

Rob


U.S. Army retired
2016 Grand Design Reflection 337RLS
MOR/ryde independent suspension, disc brakes, LR G tires
PullRite OE 18K, Demco Glide Ride pin box
2012 F350 CC DRW Lariat 6.7
Full-time since 8/2015

Grit dog

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Posted: 05/02/19 03:06pm Link  |  Quote  |  Print  |  Notify Moderator

The best bet would be to close this thread and recommend that audiodane read the PLETHORA of "discussions" regarding this very same topic that happen regularly on this board and many others.

FWIW, the answer lies in how intent you are on staying within the mfgs gvw rating which is artificially low due to the max gvws for each vehicle class and the vehicle they (and the other pickup mfgs) use for 10,000lb class 2 vehicles.
Or, being an engineer, you can deduce through research that most of the ratings are very conservative on class 2 trucks, some are absurdly conservative and decide how comfortable you are being a rule breaker! Lol
Good luck truck shopping!


03 Arctic Fox 860
07 Dodge 2500 deezul
"Obviously I don't want to overload my truck and be unsafe, but the reality is the truck is way more capable than the 10K GVWR they put on the sticker.
KJ"

audiodane

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Posted: 05/02/19 03:10pm Link  |  Quote  |  Print  |  Notify Moderator

Second Chance wrote:

Use 23% of a fifth wheel's GVWR to estimate loaded pin weight. If you have a family and are planning on a fifth wheel and carrying everyone in a crew cab, forget any 3/4-ton truck and go straight for a 1-ton SRW minimum. There are lots of folks out there who are members of the "Two-Timers' Club" - those who didn't buy enough truck the first time around and had to eat the depreciation and upgrade.


Thanks for the feedback, Rob. We're kind of already doing that (van -> expedition -> ??) ...

But for every personal experience / opinion like yours that I receive, I receive an equal number of personal experiences/opinions that say the opposite (that a 3/4 ram 2500 is just fine).

Can you give me any concrete reasons why the two sets of equations above don't line up? Something to which the engineer in me can say, "ahhh, that makes sense?"

Otherwise this and other forums leads to a big game of "he said/she said." Which while well-intended, still subjective rather than objective.

cheers,
..dane

audiodane

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Posted: 05/02/19 03:17pm Link  |  Quote  |  Print  |  Notify Moderator

Grit dog wrote:

The best bet would be to close this thread and recommend that audiodane read the PLETHORA of "discussions" regarding this very same topic that happen regularly on this board and many others.

FWIW, the answer lies in how intent you are on staying within the mfgs gvw rating which is artificially low due to the max gvws for each vehicle class and the vehicle they (and the other pickup mfgs) use for 10,000lb class 2 vehicles.
Or, being an engineer, you can deduce through research that most of the ratings are very conservative on class 2 trucks, some are absurdly conservative and decide how comfortable you are being a rule breaker! Lol
Good luck truck shopping!


thanks gritdog. I assure you, I *have* spent many dozens of hours reading posts here and on other forums, and most of them end up getting into "he said/she said" wars, disagreements, and arguments.

your second paragraph ("FWIW, ..") is along the lines of what I *have* been deducing (and more or less said as much in my OP). That's why I wanted to post a VERY specific example, using VERY specific numbers, in hopes to iron out a VERY specific answer. Either the gvw's *do* matter (and if so, why?), or they are just used for vehicle class ratings by the manufacturers (in which case, they can largely be ignored).

and fwiw, I never said I was a *good* engineer. lol!

..dane

rhagfo

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Posted: 05/02/19 03:29pm Link  |  Quote  |  Print  |  Notify Moderator

Second Chance wrote:

Use 23% of a fifth wheel's GVWR to estimate loaded pin weight. If you have a family and are planning on a fifth wheel and carrying everyone in a crew cab, forget any 3/4-ton truck and go straight for a 1-ton SRW minimum. There are lots of folks out there who are members of the "Two-Timers' Club" - those who didn't buy enough truck the first time around and had to eat the depreciation and upgrade.

Rob


X2 to this!

Sure the HD 2500 will pull the 5er, and likely be under rear axle rating. The thing is you are adding the front and rear axle ratings, with a 5er you typically only add a few pounds to the front axle, what you look at is the rear axle rating.
In addition you are making some pretty tight numbers to get a 2500 to work for you.

You describe the difference in Payload between 2500 and 3500 SRW as " The 3500 SRW increases payload but not much more." Well GVWR difference is 2,300# and you will gain most of that in Payload. I would consider that a lot more.

You have a family of five, at least three of those members will gain weight over the next several years, have you accounted for that?

Unless you buy a 2019 Ram 2500, you only have get a 3.42 differential, with a 3500 SRW you can get a 3.42, or 3.73. I think 4.10 is DRW only before 2019.

Then if you chose to get a larger 5er!

I am not a Weight Cop, I towed a 12,500# 5er with a 2001 Ram 2500, by axle rating did fine. What ate at me was I was 1,700# over the trucks GVWR. If not at fault, a hungry lawyer might drag me into civil court for being at least a percentage at fault for being over weight.

Now days I have 1,300# of spare payload!!!


Russ & Paula the Beagle Belle.
2016 Ram Laramie 3500 Aisin DRW 4X4 Long bed.
2005 Copper Canyon 293 FWSLS, 32' GVWR 12,360#

"Visit and Enjoy Oregon State Parks"


Second Chance

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Posted: 05/02/19 03:41pm Link  |  Quote  |  Print  |  Notify Moderator

audiodane wrote:

Second Chance wrote:

Use 23% of a fifth wheel's GVWR to estimate loaded pin weight. If you have a family and are planning on a fifth wheel and carrying everyone in a crew cab, forget any 3/4-ton truck and go straight for a 1-ton SRW minimum. There are lots of folks out there who are members of the "Two-Timers' Club" - those who didn't buy enough truck the first time around and had to eat the depreciation and upgrade.


Thanks for the feedback, Rob. We're kind of already doing that (van -> expedition -> ??) ...

But for every personal experience / opinion like yours that I receive, I receive an equal number of personal experiences/opinions that say the opposite (that a 3/4 ram 2500 is just fine).

Can you give me any concrete reasons why the two sets of equations above don't line up? Something to which the engineer in me can say, "ahhh, that makes sense?"

Otherwise this and other forums leads to a big game of "he said/she said." Which while well-intended, still subjective rather than objective.

cheers,
..dane


Dane,

As an engineer you know that equations are theoretical. Where the rubber meets the road (pun intended) with towing RVs is with actual CAT scale weights. The published numbers from the truck manufacturers are general and - you don't really know what kind of payload you have left until the truck is optioned out, fueled up, loaded with people, gear, hitch, pets, etc., and taken to the CAT scales. Once you subtract the loaded weight (front and rear axles separately) from the GVWR and GAWR numbers on the door sticker, you don't have "real" numbers for the truck. If you don't yet own the truck, sticker numbers off an existing truck on the lot are better than brochure numbers. You can then add up all the things listed above and subtract from the sticker numbers.

Toy haulers and front-living fifth wheels can vary in the percentage of weight they put on the pin, but the 23% of GVWR is a pretty reliable starting point. The published pin weights from the manufacturers are empty - without batteries, propane, water, waste, or anything you load in the RV.

Example: our Reflection fifth wheel is considered a "mid-profile" (i.e. mid-weight) fifth wheel RV. Its GVWR per the manufacturer (and not changed by our suspension upgrade, tires, etc.), is 13,990 lbs. Loaded for just the two of us, the trailer weighs 13,980 (About 400 lbs. of that is unsprung weight with the MOR/ryde independent suspension, so I'm not worried about being so close on that one) and puts a little over 3,000 lbs. of that on the pin. With our previous GMC 2500HD diesel crew cab (2WD, I might add - 4WD trucks will have less), the truck had 3,150 lbs. payload left per the CAT scales. That was not much safety margin for our RV. As full-timers, we moved up to a DRW 1-ton truck when we had the opportunity and have never regretted the move.

The cost difference is minimal between similarly equipped 3/4-ton and 1-ton trucks. Look for a SRW 1-ton with the most payload you can get. All the calculations in the world can't justify scrimping on safety when it comes to your family and others on the road.

Rob

Grit dog

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Posted: 05/02/19 04:02pm Link  |  Quote  |  Print  |  Notify Moderator

"The cost difference is minimal between similarly equipped 3/4-ton and 1-ton trucks. Look for a SRW 1-ton with the most payload you can get. All the calculations in the world can't justify scrimping on safety when it comes to your family and others on the road."

Except from a safety standpoint, a 3/4 and a 1 ton srw ARE the same trucks (yes, RAM has rear coils on the 2500 now and yes you could get a 3500 RAM with more power and a different trans).
BUT from a safety standpoint apples to apples, there is no additional "safety" to be gained in a 1 ton srw. Other than a 3/4 ton may need some supplemental rear suspension as the springs are typically softer. But even in that case, the "safety" aspect is lie with the owner to recognize a and possibly rectify an obvious and easily remedied condition.

Grit dog

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Posted: 05/02/19 04:12pm Link  |  Quote  |  Print  |  Notify Moderator

audiodane wrote:



thanks gritdog. I assure you, I *have* spent many dozens of hours reading posts here and on other forums, and most of them end up getting into "he said/she said" wars, disagreements, and arguments.

your second paragraph ("FWIW, ..") is along the lines of what I *have* been deducing (and more or less said as much in my OP). That's why I wanted to post a VERY specific example, using VERY specific numbers, in hopes to iron out a VERY specific answer. Either the gvw's *do* matter (and if so, why?), or they are just used for vehicle class ratings by the manufacturers (in which case, they can largely be ignored).

and fwiw, I never said I was a *good* engineer. lol!

..dane


Lol, not sure I am either, but rest assured, this conversation will most likely end up the same.
As an engineer, you would look at the individual components and see if the sum of those components is the same for 2 different "things".
In the case of pickup trucks (save for the minor differences in Rams that I mentioned above, oh and Ford now has an even more beefy rear axle for the 1 ton srw compared to the srw but the srw axle is still rated waaaay higher than the "rated" class 2 payload), the sum of all the same parts = the same answer and this is what is happening here.
Typical class 2 trucks (8 lug 3/4 ton trucks, please some try hard, don't bring up the old 7 lug Fords and 1500HD GMs) are the same truck as the Class 3 single wheel counterparts, but they are intentionally de-rated to fit within this weight class.
You can do a he said/she said argument about why, but practical application is it allows companies to have HD pickups without having to maintain DOT driver files. It allows HD pickups to run on "no commercial traffic" highways in states that have those restrictions. It allows Joe blow to own a HD pickup and park it in his overly covenanted cookie cutter subdivision without the HOA "cops" hassling him.
And the other real world advantage is given the 3/4 ton truck popularity in the US vs the 1 ton. If shopping for a used truck, there are many more 3/4 tons to choose from.

BUT the most important part is the first part. Same axles, same brakes, same frame, same wheels, same drivetrain, same, same, same = its not unsafe to do "1 ton" duties with a 3/4 ton.

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