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  1. #31
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    Quote Originally Posted by BobKilmer View Post
    It definitely is possible to estimate the impact of any weight change to the overall pin weight. All you need is the baseline weight, the location of the weight to be added, and the actual amount of weight to be added. I built a spreadsheet for my 381M to do just this.

    The theory behind this is straightforward. Not to get too much into the details, but when you add a weight to the trailer a new static balance will be established. By looking at the torques around the axles and the pin it is possible to calculate the impact on the pin weight and axle weight. My spreadsheet has entries to compute the impact of adding fuel, water, waste, or general cargo to the RV. Here are some examples for my particular unit:

    Configuration as delivered:
    - Total weight 15,084 pounds
    - Pin weight 2,650 pounds, 17.6%

    Impact to the base configuration of adding 1,000 pounds to the garage (in my case an ATV and motorcycle:
    - Total weight 16,084 (Up by 1,000 pounds)
    - Pin weight 2,247 (dropped by 403 pounds), 14.0%
    Notice the pin weight and the percentage dropped because the weight is behind the axles.

    Impact to the base configuration of filling the two fresh water tanks (104 gallons basically over the axles, 52 gallons slightly behind the axles)
    - Total weight 16,385 pounds (Up by 1,301 pounds)
    - Pin weight 2,635 (down by 15 pounds), 16.1%
    Adding a lot of weight here did not change the pin weight because the additional weight is mostly over the axles.

    Impact to the base configuration of traveling with full main gray and black tanks (each tank is 52 gallons about 12 feet in front of the axles)
    - Total weight 15,591 (Up by 867 pounds)
    - Pin weight 3,036 (up by 386 pounds), 19.0%
    This configuration adds a high percentage to the pin weight because the weight is well ahead of the axles.

    To check this with real world data and to answer your question about what the total pin weight could be, here are the measured values from my typical load including an ATV, motorcycle, groceries, the washer and dryer I added, tools, and so on. This is from a CAT scale:
    - Total weight 18,700 pounds (Up 3,616 pounds over my base configuration)
    - Pin Weight 3,060 (Up 410 pounds from my base configuration), 16.4%.
    Notice that adding 3,616 pounds of total weight only added 410 pounds to the pin, so about 11% of the additional weight went to the pin and 89% to the axles. This is why the rules of thumb for a toyhauler about how much the pin weight changes for a total weight change don't give accurate answers.

    I could try to make a very unbalanced load by taking my typical load and removing the ATV and motorcycle and also traveling with full waste tanks. This would increase my pin weight quite a bit:
    - Total weight 18,387 (down 313 from my typical configuration)
    - Pin weight 3,929 (up 869 from my typical configuration), 21.4%
    However, this is not a very realistic scenario for me. Given this is a toyhauler, I typically keep my toys in it for traveling and I never travel far with anything but empty waste tanks.

    Rather than using the rule of thumb of saying the maximum pin weight is 20-25% of the total weight I think you are better estimating the realistic total pin weight can increase by up to 11% of the total cargo carrying capacity. I showed in the last scenario that can change with your loading, but it should give a better answer than just taking a percentage of the total trailer weight.

    P.S. I expect to get many comments about needing more pin weight for a stable tow, what happens when you put every tool you own in the front cargo bay, and many other scenarios poking holes at the above. My experience from 18 months towing with my F-350 SRW is it is a smooth and stable tow, no issues with stability from winds or passing trucks, and easy to load without worrying about too much pin weight.
    This is great information! I have a 380TH.
    Smaller garage configuration, but just about same overall length. However my washer dryer is in the nose cone vs garage.


    Sent from my iPhone using Tapatalk

  2. #32
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    Quote Originally Posted by BobKilmer View Post
    You're welcome, I am glad you found the data helpful. Hopefully someone with a 351M can provide their actual numbers as well. ....
    I did a bit more digging and found a post w/ some details on the 351M I didn't see the first couple of times I looked. Not quite as detailed as yours, but has some good base numbers for the 351M.
    https://www.mygrandrv.com/forum/show...-Momentum-351M

  3. #33
    Rolling Along cookinwitdiesel's Avatar
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    It is not a Momentum, but let me offer some data on my 3740BH-R for reference.

    "Dry Pin Weight" advertised online is 2900#

    I have my tools in pass through, batteries/inverter/solar installed, 40# propane tanks (upgraded), Onan generator added, Washer and Dryer in front closet. Replaced 1621HD Pin Box with a Reese GooseBox 20k. My REAL pin weight is a hair over 4k. I added probably 1500# of food and supplies in the rear bunk room, that paired with adding the full-coverage solar dropped my pin weight only 80# (but raised the total trailer weight by 2500#)
    2019 GMC Sierra 3500HD Denali Diesel DRW (Crew Cab | 8 Ft bed | OEM Puck System | Curt Gooseneck Ball for OEM Puck | Timbrens on rear axle)
    2019 Grand Design Solitude S-Class 3740BH-R Fifth Wheel (Onan 5500W LP Generator | MORryde CRE3000 and HD Shackles/Wet Bolts | 3x MORryde Cross Members | 8k Axles and Disc Brakes | Sailun S637 ST | Reese GooseBox 20k 2nd Gen | Splendide Stackable Washer and Dryer)
    Full Suite of Victron Energy Products (2x 5k 24v Quattro Inverter/Charger | 2x 25.6/200 LFP Smart LiFePO4 Batteries | 2880w of Solar Panels across 4x MPPTs | Cerbo GX)

  4. #34
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    Quote Originally Posted by cookinwitdiesel View Post
    It is not a Momentum, but let me offer some data on my 3740BH-R for reference.

    "Dry Pin Weight" advertised online is 2900#

    I have my tools in pass through, batteries/inverter/solar installed, 40# propane tanks (upgraded), Onan generator added, Washer and Dryer in front closet. Replaced 1621HD Pin Box with a Reese GooseBox 20k. My REAL pin weight is a hair over 4k. I added probably 1500# of food and supplies in the rear bunk room, that paired with adding the full-coverage solar dropped my pin weight only 80# (but raised the total trailer weight by 2500#)
    Your data is a good example of why the rule of thumb of 20-25% of the total weight may be good for a non-toyhauler 5th wheel, but not for a toyhauler. The structure for the garage in the back adds significant load behind the axles that greatly helps reduce the pin weight. The toyhaulers also have tend to have less basement storage for heavy items like tools. My tools are in the garage along with the washer and dryer, all helping reduce the pin weight.

  5. #35
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    Quote Originally Posted by LMychajluk View Post
    I did a bit more digging and found a post w/ some details on the 351M I didn't see the first couple of times I looked. Not quite as detailed as yours, but has some good base numbers for the 351M.
    https://www.mygrandrv.com/forum/show...-Momentum-351M
    That is excellent data on the 351M!

  6. #36
    Rolling Along cookinwitdiesel's Avatar
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    Quote Originally Posted by BobKilmer View Post
    Your data is a good example of why the rule of thumb of 20-25% of the total weight may be good for a non-toyhauler 5th wheel, but not for a toyhauler. The structure for the garage in the back adds significant load behind the axles that greatly helps reduce the pin weight. The toyhaulers also have tend to have less basement storage for heavy items like tools. My tools are in the garage along with the washer and dryer, all helping reduce the pin weight.
    I am for sure front heavy. But one important point was that I added about 1500# behind the axles at the back of the trailer (same placement as a garage) and it barely impacted my pin weight. I would not count on a loaded garage lightening up the pin weight much.
    2019 GMC Sierra 3500HD Denali Diesel DRW (Crew Cab | 8 Ft bed | OEM Puck System | Curt Gooseneck Ball for OEM Puck | Timbrens on rear axle)
    2019 Grand Design Solitude S-Class 3740BH-R Fifth Wheel (Onan 5500W LP Generator | MORryde CRE3000 and HD Shackles/Wet Bolts | 3x MORryde Cross Members | 8k Axles and Disc Brakes | Sailun S637 ST | Reese GooseBox 20k 2nd Gen | Splendide Stackable Washer and Dryer)
    Full Suite of Victron Energy Products (2x 5k 24v Quattro Inverter/Charger | 2x 25.6/200 LFP Smart LiFePO4 Batteries | 2880w of Solar Panels across 4x MPPTs | Cerbo GX)

  7. #37
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    Quote Originally Posted by cookinwitdiesel View Post
    I am for sure front heavy. But one important point was that I added about 1500# behind the axles at the back of the trailer (same placement as a garage) and it barely impacted my pin weight. I would not count on a loaded garage lightening up the pin weight much.
    The numbers in my post were verified with a CAT scale so I am quite comfortable I get the pin weight changes I noted.

    The same is true for the 351M data at the link posted above. In that case a 1,020 pound Spyder in the garage reduced the pin weight by 280 pounds as verified by a CAT scale. I get a bigger reduction than this from my 1,000 pounds of ATV/Motorcycle because I have them at the back of the longer garage on the 381M.

  8. #38
    Rolling Along cookinwitdiesel's Avatar
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    Quote Originally Posted by BobKilmer View Post
    The numbers in my post were verified with a CAT scale so I am quite comfortable I get the pin weight changes I noted.

    The same is true for the 351M data at the link posted above. In that case a 1,020 pound Spyder in the garage reduced the pin weight by 280 pounds as verified by a CAT scale. I get a bigger reduction than this from my 1,000 pounds of ATV/Motorcycle because I have them at the back of the longer garage on the 381M.
    I must be underestimating the difference in geometry and weight distribution of a normal fifth wheel vs a toy hauler then. Hopefully this is all useful for the OP!

    You can see in my scale weights below, I added about 2500# between the 2nd and 3rd line. That breaks down to about 500# in passthrough for inverters, batteries, electronics. 500# distributed end to end on the roof for 14x solar panels. 1500# in the bunkhouse at the back of the RV and well behind the axles of food, drink, supplies (we completely cleaned out our house and loaded it all into the trailer). Yes, I know we were well over weight for the rating of our trailer, axle and spring upgrades are happening next week and we should never be loaded that heavy again (not planning to move again any time soon, quite the hassle haha). See where these loads and axles are located in below image of my floorplan.
    Click image for larger version. 

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    Last edited by cookinwitdiesel; 10-09-2020 at 07:20 AM.
    2019 GMC Sierra 3500HD Denali Diesel DRW (Crew Cab | 8 Ft bed | OEM Puck System | Curt Gooseneck Ball for OEM Puck | Timbrens on rear axle)
    2019 Grand Design Solitude S-Class 3740BH-R Fifth Wheel (Onan 5500W LP Generator | MORryde CRE3000 and HD Shackles/Wet Bolts | 3x MORryde Cross Members | 8k Axles and Disc Brakes | Sailun S637 ST | Reese GooseBox 20k 2nd Gen | Splendide Stackable Washer and Dryer)
    Full Suite of Victron Energy Products (2x 5k 24v Quattro Inverter/Charger | 2x 25.6/200 LFP Smart LiFePO4 Batteries | 2880w of Solar Panels across 4x MPPTs | Cerbo GX)

  9. #39
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    Quote Originally Posted by cookinwitdiesel View Post
    I must be underestimating the difference in geometry and weight distribution of a normal fifth wheel vs a toy hauler then. Hopefully this is all useful for the OP!

    You can see in my scale weights below, I added about 2500# between the 2nd and 3rd line. That breaks down to about 500# in passthrough for inverters, batteries, electronics. 500# distributed end to end on the roof for 14x solar panels. 1500# in the bunkhouse at the back of the RV and well behind the axles of food, drink, supplies (we completely cleaned out our house and loaded it all into the trailer). Yes, I know we were well over weight for the rating of our trailer, axle and spring upgrades are happening next week and we should never be loaded that heavy again (not planning to move again any time soon, quite the hassle haha). See where these loads and axles are located in below image of my floorplan.
    Click image for larger version. 

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    I am really surprised you didn't see more of a pin weight reduction given where the load was in the back of the RV. It looks like the weight is pretty far back from the axles so I would have expected to see a higher pin weight reduction.

    I like the spreadsheet and the way you showed the axles and load location on the image!

  10. #40
    Rolling Along cookinwitdiesel's Avatar
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    Quote Originally Posted by BobKilmer View Post
    I am really surprised you didn't see more of a pin weight reduction given where the load was in the back of the RV. It looks like the weight is pretty far back from the axles so I would have expected to see a higher pin weight reduction.

    I like the spreadsheet and the way you showed the axles and load location on the image!
    I was also surprised, certainly could USE the pin weight reduction haha - right at the rated limit for the GooseBox (thing is a champ!)

    I cannot load much at all into the mid area of my trailer due to the slides. Fridge and Pantry is it. Fresh tank is right over the axles. You can see why I was a little skeptical of the talk about large changes in pin weight from a loaded garage! I had as much weight in my bunk room as most would a garage.

    I do not have a picture of fully loaded, but we really went to town....lol

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    Last edited by cookinwitdiesel; 10-10-2020 at 08:45 AM.
    2019 GMC Sierra 3500HD Denali Diesel DRW (Crew Cab | 8 Ft bed | OEM Puck System | Curt Gooseneck Ball for OEM Puck | Timbrens on rear axle)
    2019 Grand Design Solitude S-Class 3740BH-R Fifth Wheel (Onan 5500W LP Generator | MORryde CRE3000 and HD Shackles/Wet Bolts | 3x MORryde Cross Members | 8k Axles and Disc Brakes | Sailun S637 ST | Reese GooseBox 20k 2nd Gen | Splendide Stackable Washer and Dryer)
    Full Suite of Victron Energy Products (2x 5k 24v Quattro Inverter/Charger | 2x 25.6/200 LFP Smart LiFePO4 Batteries | 2880w of Solar Panels across 4x MPPTs | Cerbo GX)

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