How The Weight Distributing Hitch Works

[Mr. Adventure]

Ever wonder what the WDH does for you? Ever want to think about what some adjustments might accomplish? Need to re-balance your load to improve weight distribution?

We've talked about WDH's on many threads in this forum, occasionally involving heated conjecture. The WDH calculator spreadsheet analyzes axle weight effects with or without a WDH for any trailer and tow vehicle.

The Scale Calculator spreadsheet takes axle weights from a trip to the scales and calculates tongue weight and margins relative to Gross Axle Weight Ratings (on the driver side door posts) and the Gross Combined Weight Rating (usually on the doorpost or in the Owner's Manual).

For good weights, weigh:
1) All three axles when hitched and ready for the road (your rig, loaded and ready to go).
2) All three axles with the WDH bar chains slacked (simulates what it would be like without a WDH).
3) Leave the trailer in the parking lot and weigh just the two tow vehicle axles (Gets just the TV axles, without the trailer).

(The last time I did this, the Cat Scale had 3 scale segments and the people let me do the first weigh for $10 and the 2 subsequent ones for $1 each)

The scale calculator spreadsheet will figure out the tongue weight, so there's no need to weigh the trailer separately.


Note: The WDH calculator spreadsheet was updated 3-9-12, and the Scale calculator was updated 3-5-12
(Ok, so I'm probably not the first guy who had something working while it was spread all over the bench, and then screwed it up by accident while trying to make it pretty)

[Barb&Tim]

Edit:When first posted, was getting a download error from the board, Mr. A fixed it so all is:

Ok now!

[wbmiller3]

It worked for me...Firefox on Windows 7, if it matters.

Worked for me with Firefox on my Mac. Had to specify Excel as the application but that was all.

Cool spreadsheet. Thanks!

Keith

[scrubjaysnest]

From what I remember from my statics handbook looks real good Mr A., Close enough for the kids we play with any how.

I have the following dimensions for my truck/trailer:
Wheelbase: 145"
Overhang: 59.5"
Hitch ball to trailer axle: 205"
Hitch ball to bar chains: 27"

You have my recent CAT scale weights already reported in the Elkmont section. I used the tongue weight of 580# and "weight added to trailer axle by WDH" of 160#.

Cells e22-e24 refer to "unhitched" weight of the truck axles and trailer axle.
I have never measured the "unhitched" weight of the trailer axle, but do have the numbers for the unhitched truck axles. What I think you mean is the trailer axle weight when the WDH spring bars are slacked. So that is what I entered.

Your predicted non-WDH weight distribution is pretty close, within a few tens of #s.

However the predicted WDH weight distribution is off by several hundred #s on the TV's drive and steer axles. Assuming I've got everything put in correctly.

To be honest, I'm not sure how useful these calculations are. If a person already knows the tongue weight of their trailer and the additional weight on the trailer axle caused by the WDH, then they should also already know how the WDH is shifting weight between the drive and steer axles.

[Mr. Adventure]

Originally Posted by brulaz

...
Cells e22-e24 refer to "unhitched" weight of the truck axles and trailer axle.
I have never measured the "unhitched" weight of the trailer axle, but do have the numbers for the unhitched truck axles. What I think you mean is the trailer axle weight when the WDH spring bars are slacked. So that is what I entered...

The weight of the trailer axle is the same whether unhitched or hitched without a WDH (the number gets automatically copied to the other column).

Your predicted non-WDH weight distribution is pretty close, within a few tens of #s.

Thanks!

However the predicted WDH weight distribution is off by several hundred #s on the TV's drive and steer axles. Assuming I've got everything put in correctly.

Uh, yeah it would be great to be able to blame you, but there's apparently an error in cell H22, where we'd like to be seeing 3280 for you instead of 3680, and in cell H23 we'd like to see 3960 instead of 3540. Guessing from the tongue weight distributions that are coming up, it looks like I've got some calcs for the rear axle in the front axle box. We'll try this again after I've fixed it. I appreciate having your numbers to validate the spreadsheet, if nothing else!

To be honest, I'm not sure how useful these calculations are. If a person already knows the tongue weight of their trailer and the additional weight on the trailer axle caused by the WDH, then they should also already know how the WDH is shifting weight between the drive and steer axles.

True. But the point of the WDH calculator spreadsheet is to allow people to estimate the effects of a WDH with different settings, different tow vehicles, shorter/longer wheelbases, hitch extensions, different trailers, different WDH bar capacities, etc.

Note: updated and corrected spreadsheets have been posted on the original posts on this thread on 3-9-12.

I assume your spreadsheet is based on Ron Gratz's WDH analysis?
If you haven't seen it, you should. Just google "Ron Gratz's WDH"

I also double checked the measurements, and they look good.

[Mr. Adventure]

Originally Posted by brulaz

I assume your spreadsheet is based on Ron Gratz's WDH analysis?
If you haven't seen it, you should. Just google "Ron Gratz's WDH"

I also double checked the measurements, and they look good.

Nope, never heard of Ron Gratz. The spreadsheet is my own, but I'd be happy to look at others. It's important that the spreadsheet works, because if it works it shows that we really understand the WDH.

I've attached a pdf that contains Ron Gratz's analysis.