Weight Distro Hitch. What it does/doesn't do

#1

Bottom line. In a static situation, a weight distro hitch doesn’t move much weight from the truck’s rear axles to the front. The real impact of a weight distro hitch isn’t felt until a rig tries to porpoise. When that happens, the weight distro hitch pushes back against the porpoising, reducing it’s peak amplitude and also helping to rapidly end the cyclical porpoising action.

Discussion. #'s from this post. Working trailer tongue weights on a truck scale - Paddock, Spares and Towing - SpecE30 Community Forum

Truck weights
F 3200
R 2820

Loaded trailer weight 8520 lbs.

Weights hooked to trailer but no WDH
2880
3880
7760

Weights hooked to trailer with WDH on
3020
3700
7780

What this tells us.
-The WDH hitch moved 160-180lbs difference, from the truck’s rear axle to it’s front. Not much compared to the weight normally on that axle.
-The WDH move 20lbs off of the trailer’s axles and on to the truck.

What’s interesting about this. A lot of folks have the idea that a WDH moves a lot of weight from the truck’s rear axles to it’s front. People will talk about “leveling” the truck using their WDH. But we can see here that all the WDH did was remove ~170lbs from the rear and add the same amount to the front. Not a way in hell that you’re going to level a truck by moving such a paltry amount weight.

People also talk about WDH’s keeping the truck’s front weighted for improved steering control. I’m talking a static situation where there’s no porpoising. There’s almost 3000lbs on the truck’s front axle–no way putting another ~170lbs on the front axle is going to make a difference.

The WDH was set pretty tight. I have to use the trailer jack to lift up the center of the rig in order to hook up the WDH. If a person hooks up their WDH w/o raising the center of the rig, the WDH is probably doing nothing.

#2

I got into some conversations with some pretty experienced guys in an Ecodiesel forum on this issue. We looked over a number of WDH hitch designs and different experiences. One guy had scale #'s. I also read the installation instructions of a number of different hitch designs. Interesting points:

  1. Hitch installation instructions varied a lot. The most common WDH design is what I have. Several outfits make clones. The key element of the installation instructions is telling the consumer how tight to set their bars. For example, Andersen says to tighten the bars until the truck is level. That’s problematic because every consumer is going to have a different situation. Trucks are all over the map in rear spring rate, some have airbags, a truck can have weight in the bed and a trailer can have too much weight forward. The “make the truck level” guidance doesn’t account for any of that so there’s no way that consumers are putting their drawbars with pretty close to the same amount of tension.

Another example was that the instructions from Curt said that the drawbars were properly tight when they were horizontal. That was especially bad guidance because the hitch can be tilted in order to make small changes in height of the ball. So one person might run the hitch vertical and put 50lbs on the drawbars to get them horiz and another person my tilt their hitch, jack up the center of their rig a bunch, and put 300lbs on their drawbars to get them horiz.

My Harbor Freight WDH is a clone of the Curt design. It’s instructions say jack up the center of the rig by 3" and then fasten up the drawbars. That strike me as a lot better guidance then what Curt provided in that the consumers are likely to all end up at a relatively standard amount of bending moment at the hitch.

  1. How tight is your WDH? The other thing I learned in those conversations is that some folks are getting their WDH a helova lot tighter than I am. “Tighten your WDH until your truck is level?” Wow! With my sissy soft Ram springs, my truck is no where near level–it’s darn near on the bumpstops. That’s why I have airbags in the rear in order to get some suspension travel back.

For my next roadtrip, I’m going to jack my rig up a bit higher and put the WDH up one more chain link. The HF guidance was 3" and I was prob only doing 2". What I really need to do is go weigh the rig with the WDH at both settings and see how much more weight is xferred rear to front. The guy that came to the conversation with a really tight WDH had several times my weight xfer.

Just be advised that really tight drawbars put a lot of bending moment on the hitch’s fastening points to the frame of the truck. Don’t go crazy on making your drawbars tight or the next time your rig porpoises you may be in for a big surprise. Be a bummer for the truck’s hitch to completely rip off the frame.