ColbyL

I came across this thread about the physics behind the WD hitch. It's a good read and really changed my reality on the subject! I learned how such factors as TV wheelbase, and ball to TT axle distance affect weight distribution.

https://www.rv.net/forum/index.cfm/f...pging/1/page/1

The first post was edited after 18 pages of posts, to get the verbiage right, so quotes of the first post may not match what is there.

brulaz

Yes, Ron Gratz is the Guru of WDHs.

11screw50

That example would be much better if it started with a theoretical tongue weight and how that changes loading on the axles to begin with and then went into how the WDH works to return weight to the front axle.

So, for example:
Tongue weight: 1000#
TV wheel base: 145"
TV rear axle to coupler: 65"
Ball to TT axle; 228" (19ft)

Just by dropping the tongue on the ball:
Weight removed from front axle (using rear axle as fulcrum)
1000# * 65" / 145" = 448.27#

Weight added to rear axle
1000# + 448.27# = 1448.27#

So, to add 448.27# back to the front we have two variables (I could probably reduce this but it was quicker to use his formulas)
X = spring bar force
Y = weight transferred to rear axle

448.27# = Y * (228+64)/145 (using rear axle as fulcrum)
448.27# = 2.02Y
Y=221.84#

X*(30/228)=Y=221.84#
X=221.84# / (30/228)
X=1685.98#

So the WDH
ADDS 448.27# to the FRONT axle
REMOVES 670.11# from the REAR axle
ADDS 221.84# to the TT axles.

In this example, the net weight added to the rear axle is 778.16# (1448.27-670.11) once everything is hooked up. Now, I did ignore the weight of the WDH itself. In practice, that would remove some weight from the front axle as well and would need to be accounted for in the calculations.

This is where the head tilt comes in to play as that is where fine adjustments to the force the spring bars exert are made. Those 1000# bars are not always exerting 1000#.

ColbyL

11screw50, nice post, and good points made, especially regarding the variable of spring bar force. I didn't think it could just be assumed to be 1000#. Do you have the ability to create a spreadsheet for this?

Martiangod

One of the few equations that I've seen that takes into account that some tongue weight is being pushed back at the trailer axel

11screw50

Thanks.

Pretty sure there was a spreadsheet attachment in that thread at one time (maybe it was a different one, not sure).

I know I've seen a couple different ones out there, I will see if I can find them when I get a chance (If I remember, one was pretty cryptic but probably more accurate, the other was simple but I think ignored some things like the weight of the WDH).

It is odd that nobody seems to mention or factor that in...the only explanation I could come up with is that most people severely underestimate how much 'stuff' they have in their truck so if you don't factor the transferred weight in, you're probably still closer to reality with regard to payload.

Martiangod

Weird thing for you to ponder, have a trailer on back with weight dist, throw a quad in the truck and some of its weight is also pushed back at the trailer.
The only real true way to know how your loaded is to run it across an axel scale. The numbers at the scale don't lie

brulaz

ColbyL

Test post. I just spent an hour posting something and it didn't go through

ColbyL

Well, the main thing about my missing post is that the Ford manual says that after measuring the front height before and after adding full trailer weight, the front end should come down 1/4 of the way when WD hitch is engaged. the math provided by 11screw50 assumes that the front end should come down all the way. Comments?