I am sharing a spreadsheet that I developed when we had a popup and an Avalanche with only 890 available payload. I was trying to estimate the loading of the popup to optimize tongue wt, popup axle wt , and maximize trailer and TV cargo.
I have made a few mods to the spreadsheet to allow me to estimate the pin weight of the 5ers that we are considering. As we purchased the TV first (I know some of you think that is dumber than a doornail).
The spreadsheet is extremely precise (do not confuse that with accuracy--although when I used it with the popup and the subsequent TT, it was very close....The accuracy is a function of correct weights, precise location measurements....And the only accurate weights are from weighing at a certified scale!!
As an example of accuracy reduction; I use the center line measurement of the basement weights. So the 1240 lbs in the basement, is assumed to be evenly distributed -(fwd and aft) of the 29ft CL of the basement (you can enter several basement locations and weights to increase accuracy.)(see spreadsheet & drawing)
The first tab in the file is for the 366RDS with my estimated load out plan and the 2nd tab is blank...
The only two SWAGs are the weight of the tongue (pin box assembly) and the axle wts (axles, tires, brakes, wheels etc)---see step 3 below
Instructions (for other than a 366RDS):
1. Go to the tab "Blank 5er Wt and Bal"
2. Enter : B2-B9 cell data
3. Adjust B15 (Weight of Axle/Suspension) and or B14 (Weight of Tongue assmby).....my guess is about 16.5 and 3.1)....but your guess is as good as mine. You have something very close when C17 is equal to 0.
4. Enter your 5ers cargo wt and location from rear
Yell if you need help or something looks weird.
The spreadsheet is password protected for all non-input cells, to reduce the chance of ooppss....msg me and I will provide the pswd if you want to mod the file.
Note: I normally have the floor plan in the excel file but because of size restrictions with this forum I had to remove it and attach separately.
The only two SWAGs are the weight of the tongue (pin box assembly) and the axle wts (axles, tires, brakes, wheels etc)---see step 3 below
Instructions (for other than a 366RDS):
1. Go to the tab "Blank 5er Wt and Bal"
2. Enter : B2-B9 cell data
3. Adjust B15 (Weight of Axle/Suspension) and or B14 (Weight of Tongue assmby).....my guess is about 16.5 and 3.1)....but your guess is as good as mine. You have something very close when C17 is equal to 0.
4. Enter your 5ers cargo wt and location from rear
Yell if you need help or something looks weird.
DG
This spreadsheet is slicker than goose grease. I've been playing around with it and can't seem to get the B14-B15 anywhere near zero - in fact, the delta seems to diverge with a realistic B15 (I looked up the weight of my 3500 pound Dexter axles; the best I can find is a shipping weight of 70 pounds (each) which amounts to about 4% for B15 for my TT). Is the tongue value (I think you said it was the pin box for a 5er) of B14 applicable to a TT? I have to set B14 to -22% to get a zero value.
I've actually been (by hand) doing torque calculations for our TV/TT combination. No problem with determining the CoG of the TV if I use each GAWR in the free body diagram (not sure how accurate this is, but at least they are two different values) but I've been stumped on how to solve for each axle of the TT as I don't have enough information to produce two equations (and I don't know the CoG for the TT; your program will help with that). I note you used the mid-point between the axles; do they each actually share equal load?
Any thoughts on my B14-B15 issue?
Thanks.
Ken
__________________
Now: 2019 Winnebago 2500FL w/e2 WDH;Sold: 2015 Bullet Premier 19FBPR (shown)
2012 Ford F-250 Lariat Super Duty Crew Cab (gas 6.2 L, 3.73 gear ratio 2WD, 172" WB)
sorry you are having difficulties....I am not sure what the issue is though...
B14 and B15 would never be zero , if you literally mean a value of "0", and when I set them to zero (0) they go to zero.
Give me a little more understanding and I can will help..
But let me just say (this may clear up what I think maybe you are saying)
The program was originally written for a single axle camper, and I thought that I could achieve greater accuracy by taking the two big chunks of steel that was not "evenly" distributed over the entire length and calculating their moments...It was a good idea with our small lightweight (<3k lbs) camper.
And changes in the "modeled" locations in the program very accurately predicted the actual weighed values....I was a happy camper.
But then I began using it for our 2018 Freedom Express 246RKS (similar in size and weight to your TT, with one big exception....the distance between hubs appears to be much greater on TT than mine---)
The "precision" of the axle and tongue wts did not add to the "accuracy" as I could not model a 2 fulcrum /dual axle program. Because, in my TT (based on physical weightings) the distribution of weight on the two axles was not equal depending on where the weight was added. So what I did/do is leave B14&B15 blank and zero in on the "wheel center from the rear" and then tweak B14 and/B15 ,if needed,to achieve the dry pin wt, that I got when I originally weighted the TT (pre load out)....and btw it did not equal the dry tongue wt given in the specs....
Once I tweaked the empty configuration (except propane, bottles, battery, mattress, mattress cover, undrainable water, etc that isn't included in the spec's dry tongue wt)....then the loading prediction was acceptably accurate, I have weighted my TT 15-20 times , most of them in the early days to test the predicted outcome by my program....and it gave me what I was looking for
.....Now that our loadout plan is stable--the same stuff in the same location , I don't use the program as often....the last time was to determine the best location to loadout my cast iron pots and pans (65#)...
However, I am now using the heck out of it....predicting which 5er config makes the most sense with our loadout (about 1850#)...the closer the basement is to the pin the more weight will transferred to the pin and then to my TV....but how much....and this program does a reasonable job in providing the answers, but does not however replace the need to physically weight....
I have include a snap shout of your TT how I would begin...(assuming my guessed lengths are accurate....and notice I need .335 in wheel center to achieve the stated dry tongue wt.... 6/100th of an inch(5/1000th of a foot) or 1.5mm ......the model's "accuracy" is not that "precise" but precision is required to achieve reasonable accuracy...
BTW: 1. the axle wt should include, leaf springs, hubs, brakes, wheels, tires , hdware, etc....and that will be much greater than 70#.
2. if you choose not to use the axle and tongue wt-- then the measurement "A" is not needed....
3. the program really only tries to predict the center of rotation or what I call longitudinal center of gravity (LCG ) and not COG, which implies a vertical axis component as well as horizontal.
Hey Ken,
... If this did not answer the mail, shoot me a msg.
dg
DG
I interpreted your instructions incorrectly; I tried the B14/B15 adjustment with cells > B19 using data. However, when I zero out those values nothing changes above.
I tape measured "A" as 240 inches (quite close to you) and "C" as 93 inches; "C" is quite different from yours. I will go out and ensure I didn't write something down wrong. The axles are 42 inches apart.
Possibly interesting note: When I put in your B3/B4 (I used cargo wt from the trailer label on the screen door and subtracted it from the GVWR) without changing B7->B9, I get zero for C17 using B14=-22% and B15=4%. Using your values for B7 and B9 (we agreed on B8) and not changing my B14, B15 values B17/C17 is squirrely, whereas deleting those values consistent with yours gives what you show, as would be expected. I have attached images of my floorplan and spreadsheet (with your numbers in the cells; mine are off to the right).
I'll keep playing with it. I will go remeasure tomorrow and see what results.
Thanks.
Ken
__________________
Now: 2019 Winnebago 2500FL w/e2 WDH;Sold: 2015 Bullet Premier 19FBPR (shown)
2012 Ford F-250 Lariat Super Duty Crew Cab (gas 6.2 L, 3.73 gear ratio 2WD, 172" WB)
Assume you have a TT:
Dry Wt 4213
Pin/tongue Wt 410
Dim B 23.17
Dim C 93"
clear all input fields
enter dry wt
enter dry tongue wt
enter Dim B
You will have a calculated tongue wt of 2106.5 (half of the total) because the program assumes two things now....even wt distribution [as much wt aft of center line as there is wt forward of center line and wt is supported at each end of the TT.
Now add Dim C (the fulcrum) which we assume is somewhere between the axles (and probably slightly forward of center) , now the calculated tongue is 1048 because it assumes even wt distribution over the length...it is not!!
So now think of B14 and B15 being labeled :
B14 how much of the 4213 is forward of center line
B15 how much of the 4213 is aft of center line
Well to achieve 410 tongue wt then about 61% is aft of center line and 39% is forward of center line. And that makes sense to us as our refig, water heater , ac, stove etc is all aft of center line.
Now as you add values in B20 -B33 you will get a calculated/predicted tongue wt.....try it and then go weight your TT to validate.....
It told me to place my 65# of cast Iron about 2 ft from the rear to reduce about 30 lbs of tongue wt....after I did and weighted my TT , I think that it did as my CAT scales vary by as much as 100# between same day/same configuration weightings....LOL
and there is a much wt aft of 9.2 foot (from rear) as there is wt forward of 9.2 foot ....so if you wanted to pick the TT up and have equal load on either side of a single pick up point you would put your strap at 9.2 from the rear of the TT ...
My guess is that you are now as familiar/understand this spreadsheet as I am...Yes/No
so when we defined B14 as the % of wt forward of 11.584 (center line) and B15 defined as the % of wt aft of the 11.584 center line, then we no longer care about the body dimension and you must leave 0
The original program recall was for a small single axle popup . so the 3 big weights was axle, tongue, and body/stuff. So I made the model too complex....
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