ColbyL

I want to try out version 5, but have limited time right now. I am picking up the trailer in a few days, and I want to double check all weights and measures before giving any more feedback.

Montol

If you could help me narrow in on what numbers need to be considered when 'returning the 25%', that should be a fairly easy figure to put together.

I've just never actually set up a WDH, which is why the nuances of the final real-world setup are a bit muddy to me.

Also, someone really needs to confirm for me that a '6000lb towing / 600lb weight distribution hitch' really does in fact mean 600lbs of downforce per bar, equaling 1200lbs that would be entered in B53 for 'WD Spring Bar Rear End Load'. It looks like it makes sense (nearly 600lbs returns to front axle when there is a 600lb tongue weight, and when using 1200lbs in that cell), but I want to be sure, since its such a weird naming convention.

Thanks!

ColbyL

I have called Blue Ox and spoken with a "tech person", who could only give the standard response..."If the tongue weight is X, you need bars rated X".

Then I got the email address of a guy at the local Trailer dealership was supposed to know everything, and got a vague reply. I don't think anyone wants us to do this...but if we have an accident that gets someone killed, it will be proven in court that our TV rear axle was overloaded by 5 lbs.

Maybe I will attempt to contact Ron Gratz (reference to my first post).

Montol

Okay, so we need to return 25% - 50% of the (front axle load / rear axle load / total tow vehicle axle load / tongue weight load) to the front axle.

Someone circle the correct answer for me? I believe you mean rear axle load, I just want to confirm. Thanks!

ColbyL

when the tongue is lowered on the ball, weight from the front end shifts to the rear axle. When the hitch is applied, some of that weight gets "returned" back to the front.

Montol

OK - I took a hack at it for those percentage-to-return figures, and a bit more detail on how to enter the WDH numbers for clarity.

Also changed the outputs on the Hitch Calculator to show the trailer vehicle hitched axle weight instead of the trailer GVW, since that made more sense.

Now you guys get to tell me how I'm wrong, hah!

ColbyL

Montol, here is my current spreadsheet to review

Montol

Hmm, now that is a mystery. The math should be sound, and I can see what you mean by everything being close.

Just to confirm:

1) Your Sheet 1 'Base Curb Weight' was a scale measurement, and included a full tank of gas, no driver/passengers, and no cargo?

2) Your Sheet 2 'Base Curb Weight' is measured for the tongue weight and trailer axle separately (not just relying on factory specs?)

3) Your Sheet 3 'Observed' values used the same dry payload as the Sheet 1 and Sheet 2 measurements - full tank of gas, no driver/passengers or cargo?

Just trying to figure out how or where the extra 326lbs is somehow getting in there for the predicted versus observed GCVW - if we could locate that, then the FA/RA/TA figures are just math.

The two places I'd think could possibly affect it are if the combined vehicle weight had extra cargo that was missing from the original scale measurement, or if that tongue weight isn't accurate.

If the dry tongue weight is actually only 775lbs, not 1100lbs, then everything pretty much balances to your observed figures.

If the truck weight was including the driver/some gas or cargo in the first weighing, but did not include the driver/some gas or cargo in the combined weighing, then that could account for the difference too.

ColbyL

yes to all. Like I said, I want to reweigh everything and also remeasure hitch related measurements before I go much further into this. Perhaps the scale is wrong+ it does round off to the nearest 50 lbs. I'm not even sure it is used anymore and may not even be certified

ColbyL

I picked up the trailer today, but was not able to go to the scale as my batteries were weak and I wouldn't be able to unhitch/hitch as needed. I took it home and used the bathroom scale method to check the tongue weight. I previously got 1100 at the scale, but I was weighing at the jack point and not the ball point, so it is actually 1150. I believe that the scale was accurate previously. I was able to take new measurements and found some discrepancies: receiver to ball, hitch head weight, weight of bars, and also I previously weighed the truck unhitched with the hitch head attached.

So- I corrected all the data inputs and the hitched weights predicted by the spreadsheet were closer, but not quite right.

My trailer has tandem axles. Previously I used the midpoint between the axles for my ball-to-trailer axle measurement, but I wondered if that is actually right. I had the idea that maybe the front axle should be used. I measured a height on the side of the trailer, centered with the front axle, then jacked the tongue up and down quite a bit, and the measurement didn't change, so I used that measurement in the spreadsheet.

I was getting closer!

After varying the value for spring bar force, ending up with 1500 lbs, the predicted hitched weights in the spreadsheet vs. my actual hitched weights are as follows:

Front axle weight: 3058 predicted vs. 2950 actual, difference of +108 lbs.
Rear axle weight: 3356 predicted vs. 3250 actual, difference of +106 lbs.
Trailer axle weight: 5699 predicted vs. 5750 actual, difference of -51 lbs.

Conclusion: I think the spreadsheet is good as is. Many thanks to Montol for the work he put in on it.

Conclusion #2: I have not included any passengers or cargo yet, so I have not proved out that part of it yet.

I hope that others following this thread will try out the spreadsheet and post their results.
The link is at the top of page 4. You will need to click file, download as... to get it on your computer and be able to enter your own values.