Weight Distribution hitch

The link to the towing calculator is down at the bottom of my post.

Re when the spring bars will fail you need to consider them as if they were cantilevered beams, fixed at one end with a point load at the other end. That beam configuration has a moment at the fixed end of M = F x d. d is 18 inches and in my case F is about 750/2 = 375 lbs (2 bars) , so M = 6750 in-lbs.

Assuming a 1 inch bar, the section modulus is 0.098 in^3 so the stress is M/S = 6750/.098 = 68 ksi. Way past the yield of mild steel. And that is before we add a 2x factor to handle 2 g bump loads, which are common.   

I don't have my trailer or wdh anymore but I'm sure the bars on my 1000 lb wdh were larger than 1 inch dia. Unlikely they are mild steel either, spring steels are around 100 ksi or better in order to not be to stiff in deflection. I did eventually find a statement that my bars were rated at 1000 lbs each max.

In any case, the point is that you can for sure bend your wdh spring bars under bump loads if they are too light for the application. So run the calculator for your actual load case and get wdh bars rated for that. Might be 600 lbs for a light rig but not for a heavier configuration set up for boondocking. In my case an 800 lb rated wdh would have worked but been marginal. The ride was quite comfortable will 1000 lb bars so I went with that. And you are not going to bend your TV frame by using a wdh with a higher rating because if you have it set up properly the max load on the bars, frame, and trailer will be the same regardless of the wdh rating.

OG, you mention a calculator in your prior post, was there supposed to be link to it or am I missing something? 

I concur with Alan. The 2019 Highlander weighs in at about 4500lbs - similar to my 2010 Mazda CX-9. There is roughly 2200 lbs resting on the front and rear axles. The WDH pushes upwards on a large sub frame around the rear axle. The WDH is pushing upwards on the chassis about 300lbs to offset the tongue weight. At most shifting 100-150 lbs to the front axle. Likewise 100-200 lbs is being pushed back on the rear axle of the 180. This amount of weight is well within the Highlander’s chassis capability when you consider what it’s total payload capacity is (as long as you aren’t loading a ton of gear in it.) I initially tried 1000 lbs spring bars and it made the ride very harsh as every bump the trailer wheels hit was transferred to my vehicle. I switched to 600 lbs bars and the ride smoothed out nicely. Hardly notice my 171 is there.  

I had a 1000 lb rated wdh on my Highlander, no issues. When a wdh is set correctly it will exert the same moment (torque) on the tow vehicle regardless of it's rating. That is because it is intended to return the load on the front axle to what it was without the trailer. It should never be tensioned more than that.

As for unibody vs body on frame, either one can be damaged by excessive moment (torque) beyond what it is designed for. That is for the manufacturer to tell us. So if your vehicle's owners manual allows use of a wdh you can use one, within the other load limitations of your vehicle. If it is not allowed (flr example Subaru does not authorize their use) then don't do it.

I always used a wdh with my rig, the the ride and handling was much better with it. That doesn't mean you have to use one, you are free to do what you want within the limitations of your vehicle.

The flip side of that is that a single individual's experience is not statistically significant, no matter how many thousands of miles one of us drives and it is ok (or not) that doesn't mean that something is (or isn't) dangerous. To have that level of confidence requires millions of miles driven by thousands of people.

Originally posted by richfsi Greetings, just purchased a 190. I am towing with a 2019 Toyota Highlander. Looking for a recommendation for a Weight Distribution Hitch. Appreciate the help!

Isn't the Highlander built on a unibody? Are any hitches built for it that are built for weight distribution?    

My SUV and 180 does not need weight distribution, nor sway damping, but I use a friction sway damper just in case. It is a unibody and nobody makes a weight distribution rated hitch for it.