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 > calculating trailer vs 5th wheel towing capacity question

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outwestbound

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Posted: 04/11/14 11:33am Link  |  Quote  |  Print  |  Notify Moderator

Sorry to be a pest, but another question to check on methodology; not really interested in a Ford vs RAM truck dust up. I'm looking to buy a 1 ton to tow a 5th wheel. I want to know the math behind a manufacturers published tow ratings between conventional towing (tow behind) vs. a 5th wheel. It's confusing as Ford publishes these two different ratings, but RAM does not appear to. RAM is just one tow rating number and, since I'm not sure about the math and best practices, I don't know how best to interpret RAM's figure.

For example, Ford's 2014 diesel F350, auto transmission 4x4 6.7L DRW 3.73 axle ratio is conventionally rated to tow 18,500 and on a 5th wheel, 22,200. It looks like Ford took 20% of 18,500 and added that back, to get 22,200 (18.5 + 3.7=22.2). I'm guessing this 3,700 pin weight was allocated to the tow vehicle, thereby increasing the 5th wheel tow rating.

Am I correct? If so, how many times is the pin weight counted in the GCWR? (e.g., is the 3,700 pin a deduction from both truck and trailer; a total 7,400 against the GCWR?)

RAM's comparable 2014 3500 AISIN (auto transmission) DRW 3.73 is rated to tow 23,500, based on the chart in the marketing brochure I got at the dealer. RAM just provides this one figure, so how does this single figure compare to Fords' fifth wheel figure? I just want my calculations to be apples to apples, not looking at brands here, with the intent of towing a 5th wheel.

Thanks

BB_TX

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Posted: 04/11/14 11:52am Link  |  Quote  |  Print  |  Notify Moderator

I don't think you will ever know how they come up with their numbers unless you work in their marketing department. And they can change the numbers as their competitor's numbers change. Doesn't matter which brand you are looking at.

donn0128

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Posted: 04/11/14 12:00pm Link  |  Quote  |  Print  |  Notify Moderator

IMHO towing ratings are unimportant when it comes to towing a fifth wheel.
What you need to know are three things.
Real ready to travel weight of the truck.
GVWR of the truck.
Real ready to travel pin weight of the fifth wheel.
Lacking any of these items and you are only going to be guessing.

Lacking this information you might make a couple of assumptions and be close.
The current crop of 1 ton SRW crew cab truck with diesel and automatic is going to scale ready to travel right around 8000 pounds.
So, subtract from the GVWR 8000 pounds and generally speaking you are going to have around 2000-2500 Cargo Carrying Capacity (CCC)
Again generally speaking a fifth wheel is going to have between 17 and 25% of it's total weight as pin weight. Most folks consider 20% a good place to start. So, using my example above of 2000 pounds CCC on the truck and basing on 20% means you can tow a 10,000 GVWR fiver.
This is all based on a lot of assumptions and assumes you want to stay within manufacturers numbers otherwise you probably would have never asked the question in the first place.

* This post was edited 04/11/14 12:17pm by donn0128 *


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Old-Biscuit

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Posted: 04/11/14 12:05pm Link  |  Quote  |  Print  |  Notify Moderator

You 'tow' a trailer and tongue weight is lower plus use WD to adjust weight on truck

You 'carry' & tow a 5th wheel.......all pin weight is carried on rear axle (tires, axle, springs)

MFG. published MAX Tow Ratings are a misnomer and marketing hype.
"Maximum trailer weights in pounds for properly equipped vehicles with no cargo"
"Make sure vehicle payload (reduce by option weight) will accommodate trailer tongue (trailer king pin for 5th-wheel towing) load weight and weight of passengers and cargo added to towing vehicle. Addition of trailer tongue (trailer king pin for 5th-wheel towing) load weight and weight of passengers and cargo cannot cause vehicle weights to exceed rear GAWR or GVWR."

Trucks GVWR, RAWR, Tire Max Load Ratings and 'actual' payload available are the important numbers when matching truck/trailer.


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lbrjet

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Posted: 04/11/14 12:59pm Link  |  Quote  |  Print  |  Notify Moderator

Pin weight is not added twice. One number (tow behind maximum) has nothing to do with the other(fifth wheel maximum).


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Ron Gratz

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Posted: 04/11/14 03:53pm Link  |  Quote  |  Print  |  Notify Moderator

donn0128 wrote:

IMHO towing ratings are unimportant when it comes to towing a fifth wheel.
I think that is not true for a 1-ton DRW.

The 2014 F-350 DRW 6.7L 4x4-174.2 has a curb weight of 8,195# and a GCWR of 30,500#.
This means that with only a 150# driver and no optional equipment or cargo, the trailer weight would be limited to 30500-8195 = 22,305#.

The 14,000# GVWR of the same TV would allow a maximum pin weight of 14000-8195 = 5805#.
The corresponding trailer weight at 20% pin weight would be 29,025#.

The 9650# rear GAWR combined with a rear Curb Weight of 3453#, would allow a pin weight of 9650-3453 = 6197#.
The corresponding trailer weight at 20% pin weight would be 30,985#.

So, "tow ratings" are important when it comes to towing a fifth wheel if the candidate TV, as in the OP's case, is a DRW.

Quote:

The current crop of 1 ton SRW crew cab truck with diesel and automatic is going to scale ready to travel right around 8000 pounds.
So, subtract from the GVWR 8000 pounds and generally speaking you are going to have around 2000-2500 Cargo Carrying Capacity (CCC)---
Again, the OP is talking about a DRW.

Ron

* This post was edited 04/11/14 04:02pm by Ron Gratz *

BB_TX

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Posted: 04/11/14 08:09pm Link  |  Quote  |  Print  |  Notify Moderator

donn0128 wrote:

............
The current crop of 1 ton SRW crew cab truck with diesel and automatic is going to scale ready to travel right around 8000 pounds.
So, subtract from the GVWR 8000 pounds and generally speaking you are going to have around 2000-2500 Cargo Carrying Capacity (CCC)
.............

The current crop of 1 ton SRW crew cab trucks will weigh in around 8,000 lbs but they have GVWRs of 11,000 - 11,500 lbs. That puts CCC in the range of 3,000 - 3,500 lbs, and in some cases near 4,000 lbs.

Golden_HVAC

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Posted: 04/11/14 11:21pm Link  |  Quote  |  Print  |  Notify Moderator

outwestbound wrote:

Sorry to be a pest, but another question to check on methodology; not really interested in a Ford vs RAM truck dust up. I'm looking to buy a 1 ton to tow a 5th wheel. I want to know the math behind a manufacturers published tow ratings between conventional towing (tow behind) vs. a 5th wheel. It's confusing as Ford publishes these two different ratings, but RAM does not appear to. RAM is just one tow rating number and, since I'm not sure about the math and best practices, I don't know how best to interpret RAM's figure.

For example, Ford's 2014 diesel F350, auto transmission 4x4 6.7L DRW 3.73 axle ratio is conventionally rated to tow 18,500 and on a 5th wheel, 22,200. It looks like Ford took 20% of 18,500 and added that back, to get 22,200 (18.5 + 3.7=22.2). I'm guessing this 3,700 pin weight was allocated to the tow vehicle, thereby increasing the 5th wheel tow rating.

Am I correct? If so, how many times is the pin weight counted in the GCWR? (e.g., is the 3,700 pin a deduction from both truck and trailer; a total 7,400 against the GCWR?)

RAM's comparable 2014 3500 AISIN (auto transmission) DRW 3.73 is rated to tow 23,500, based on the chart in the marketing brochure I got at the dealer. RAM just provides this one figure, so how does this single figure compare to Fords' fifth wheel figure? I just want my calculations to be apples to apples, not looking at brands here, with the intent of towing a 5th wheel.

Thanks


So what you are asking is why does Ford limit the conventional trailers to only 18,500 pounds?

I think it has to do with the ability of the hitch system, rather than the possibility that the transmission, brakes, rear axle or other truck systems will be overloaded by towing a conventional trailer that is 19,000 pounds.

Ford does test it's trucks by hitching them to a 18,500 pound trailer, then going on a drive with them. Driving onto the side of the road while going 40 MPH and the right two tires end up in the dirt or gravel. This is dangerous, but if the truck or trailer become unstable, then Ford will not recommend that the truck tow a heavy load while it is unstable. If the truck is stable, then Ford can say "This is safe". Going around curves, up and downhills, if it is safe at 18,500, then Ford will say "You can tow this much".

A fifth wheel is inherently more stable than a travel trailer. So a 35' long fifth wheel being towed by a dually F-350 will be stable at 40 MPH when driven off the side of the road into the gravel, even if that trailer is 22,000 pounds.

Limiting factors on the fifth wheel include the ability of the truck to carry the hitch weight of the fifth wheel. So some manufactures will "Claim" it can tow 18,000 pound fifth wheel with a 2500 series truck. However the pin weight of most 18,000 pound fifth wheels will be about 3,600 pounds. Most 2500 series trucks can not possibly carry 3,600 pounds safely without going way over the GVWR of the truck. Even some SRW 3500 trucks can not carry that much weight and still carry a family with 4 passengers in the cab. Most RV'ers will also take along 100 pounds or more in the pickup bed, such as bikes, firewood, generator, or other camping supplies.

In 2005, Ford changed it's GVWR on the F-250 and F-350 to increase it greatly. While a 2004 F-250 would have a 8,800 GVWR, the F-250 of 2005 and later would be 10,000 pounds. The SRW F-350 has a GVWR from 11,000 to 11,500 or perhaps more (I have not looked them up lately). The DRW F-350 is even higher.

Fred.

outwestbound

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Posted: 04/12/14 07:59am Link  |  Quote  |  Print  |  Notify Moderator

Thanks for posts to my confusing question. I was trying to understand if there was a "best practice" way by those in the RV community of converting manufacturer's towing ratings to a common standard of comparison. Clearly, there is not, because current regulatory structure leaves manufacturer's to their own methodologies and procedures to arrive at their product's capabilities, leaving consumers with no objective means of comparison.

Based on numerous articles, manufactures agreed to comply with Society of Automotive Engineers (SAE) standard J2807: Performance Requirements for Determining Tow-Vehicle Gross Combination Weight Rating and Trailer Weight Rating for 2015 1/2 ton trucks. But, no agreed date has been scheduled for bigger trucks.

J2807 was available in 2013 and articles say manufacturers have been making mechanical (not just smoke and mirror changes to computational methodology) to 3/4 and 1 ton trucks, so big reductions in their figures may be minimized, once they all agree to adopt the standard. One article here, claims that the rating inflation is much greater in the 3/4-1 ton trucks; like 3,000 - 4,000#, based on 2013 figures. Hopefully if manufacturers have worked on improving mechanical capacity since 2013 as a way to minimize their embarrassment when they all agree to comply and "come clean", that the 2014 published figures aren't so inflated as they were in years past.

I want a certain % safety cushion under the truck's "capacity", so I'm taking 10% off RAM's published towing rating, just because I don't trust RAM (or any other). Then, I'm taking a second 10% (total about 20%) for my own peace. So, with the RAM 3500 I'm looking at, I'll lower my rear end gear from 3.73 (23,500) to 4.10 (29,000) to make my cushion, knowing that 23,500 is now a more reliable figure. I'll burn more fuel and run higher RPMs, just to be safer, because manufactures can't be trusted; very frustrating.

JIMNLIN

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Posted: 04/12/14 08:17am Link  |  Quote  |  Print  |  Notify Moderator

Quote:

Ford's 2014 diesel F350, auto transmission 4x4 6.7L DRW 3.73 axle ratio......
and
RAM's comparable 2014 3500 AISIN (auto transmission) DRW 3.73 is rated to tow 23,500,


Actually your not comparing apples to apples here. The Aisin transmission uses a 1:1 direct gear ratio and requires a 4.10 axle ratio to achieve max tow ratings of 29000 lbs.

Fords Torqshift 6R140 has gear splits on both sides of 1:1 so with the 3.73 rear axle ratio operates like a 4.xxx-4.30 axle ratio (depending on transmission gear selection) to achieve max towing rating.

The Ram Body Builders Guide clicky link shows all the tow rating for each configured package truck.
Look in the notes and it mentions over 17000 lb requires a GN or 5th wheel hitch for a 3500 Ram.
If your buying a fith wheel trailer I wouldn't worry about conventional trailer (TT) weights.


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