Towing - Weight Distribution Hitch compatibility

[Rossy]

I've spent some time solving for the static forces exerted on the receiver with a weight distribution hitch. Note that these measurements are approximate, and that I haven't been able to ensure equal 1/3 distribution of the tongue weight, as I assume in my diagram and calculations. Also, the measurements are specific to my modified hitch and trailer combination.

That said, I solved the attached free body diagram for the torque on the weight distribution arms t(WD) and came up with approximately 11900 in-lbs (just about 1000 ft-lbs) in order to get the distribution of weight on the axles as shown. Assuming that's where it is adjusted, I am able to solve for the moment forces created by the trailer tongue at point R, which is the connection point of the receiver into the Model X. Those forces are the 500# "max" tongue at the ball and the ~1000 ft-lbs of torque from the ball in the opposing direction. They net to -4100 in-lbs, which means approximately 342 ft-lbs of torque in the CCW direction.

So what does that mean relative to the rating of the stock Bosal hitch receiver? Well, the Bosal hitch receiver is stated to support 500lbs of downforce at 8" from the hitch pin. That equates to 500 lbs at approximately 13.5" from my location R, or 562.5 ft-lbs of CCW torque. So, given that my calculations have any merit at all, and noting that they do not include any dynamic effect, it appears that the WD hitch relieves not only the rear axle, but also the receiver from torque that would normally be applied, allowing for a larger factor of safety around tongue weight fluctuations.

I welcome (and request) any feedback on my calculations, especially if anyone sees something I've done wrong. I recognize I didn't include some of the vertical offsets, but I think the effect is minor in the statics problem. I may revisit and try to tweak it a bit.


View attachment 213415

This makes me want to go out and buy back my old Statics and Dynamics textbooks from college. Statics I managed to grasp. Dynamics I was floundering the entire summer session I took it and barely failed the final.

 

[Scrappy]

The Model X is capable of towing up to 5000 pounds with 500 pounds of tongue weight (19-20" wheels). When considering towing anything more than half of that maximum, the subject of WD (weight distribution) hitches comes up. I've seen a number of rules of thumb, but generally what I see is that if the TT (travel trailer) is more than 50% of the TV (towing vehicle)'s weight, a WD hitch is recommended. The Model X weighs ~5300 lbs, so any trailer over 2650 lbs would qualify.

First, it will be helpful to describe a typical (non-WD) towing configuration. The Model X has two axles on the ground, and the travel trailer, for ease of discussion, has a single axle on the ground. The two vehicles are connected solely by the ball hitch and safety chains. The tongue weight is the weight pushing downward on the ball hitch at rest. That weight pushes downward on the back of the Model X, and therefore pushes down the back axle while taking weight off of the front axle. As the tongue weight increases, this scenario can create instability in the form of lack of maneuverability. It can also create a situation where the trailer tilts downward at the front significantly, with the towing vehicle tipping downward at the rear and upward at the front. A tiny amount of trailer front-tilt is desired for stability reasons, but too much will also cause issues.

Weighting the trailer behind the axles can alleviate some of this and balance the load. However, too much in the back and the trailer will tilt backward. From what I understand, this is the most unstable configuration, as air under the trailer can cause lift and sway.

In comes the WD hitch. The best description I've read is that this is like standing on the front of the trailer and lifting upward on a stiff pipe inserted into the receiver on the towing vehicle. What happens when you do that is that you take weight off of the rear axle of the tow vehicle, and distribute that weight between the trailer axle and the front axle of the towing vehicle. In doing so, you create a bit of vertical plane rigidity between the two, and they act almost as one single mass.

So, that's good enough and makes plenty of sense, except my online research shows that there are some problems with this. One problem is that the Model X has a unitary body construction, and there are varying opinions on whether or not WD hitches are appropriate for that style of frame. If you imagine that rigid rod going through the receiver, and remember that it's also square, you can imagine the torque that is placed on the hitch and the vehicle whenever the road is not similar for the trailer axles and the vehicle axles. A bumpy road will transfer a lot of stress into the unibody of the Model X. The reason that's considered detrimental is that the entire body will bend and twist repeatedly, and could eventually fail. Opinions vary on whether or not this is a serious problem, and I can find no empirical data one way or the other. Tesla's use of aluminum in lieu of steel is also a big question mark in this realm.

Another problem appears to be the auto-leveling mechanism built into the Model X. This is set up so that when you attach a tow vehicle, the air suspension levels the X for you. Similar products from Mercedes and BMW suggest completely disabling this when a weight distribution hitch is attached, and most manufacturers of unibody vehicles suggest against using a WD hitch at all.

Where does that leave us? On one hand, the literature says that a travel trailer approaching more than half of our vehicle weight should use a weight distribution hitch for safety and stability. On the other hand, there is advice against it because of the unibody construction and air suspension of the X.

Are there any knowledgeable opinions on this?

*Also, any corrections to erroneous statements I've made are welcome.

Love this thread! I'm confused I searched the whole thread and couldn't figure out if you ended up going with a weight distribution hitch? If so can you tell me which one. My issue is below.

I have a query about using a 'Weight Distribution Hitch' for my 2023 X. Recently, I visited an RV dealer to purchase a 2022 Keystone RV Hideout 176BH. However, I was advised to buy a Weight Distribution Hitch even though the RV's Dry Weight is 3710 lbs and hitch weight is 520 lbs. Although I have already installed the Draw-tite Hitch Receiver, which is rated higher than Tesla's OEM hitch, it's not recommended for use with weight distribution systems. As I have seen many Tesla owners towing RV's, I'm seeking advice on whether I really need a weight distribution hitch or can I use the Reese Towpower 21536RAK 2" Drop Standard Class III Starter Kit? Any help regarding this matter would be greatly appreciated.

 

[ecarfan]

In case @ohmman doesn’t see your post, I can tell you that he did install a weight distribution-compatible Draw-tite Equal-i-zer hitch for his X. See this thread Towing...actually Airstreaming...with a Model X

The weight of your Keystone trailer is well over half the weight of your X so you should definitely use a weight distribution hitch.

 

[dmurphy]

Love this thread! I'm confused I searched the whole thread and couldn't figure out if you ended up going with a weight distribution hitch? If so can you tell me which one. My issue is below.

I have a query about using a 'Weight Distribution Hitch' for my 2023 X. Recently, I visited an RV dealer to purchase a 2022 Keystone RV Hideout 176BH. However, I was advised to buy a Weight Distribution Hitch even though the RV's Dry Weight is 3710 lbs and hitch weight is 520 lbs. Although I have already installed the Draw-tite Hitch Receiver, which is rated higher than Tesla's OEM hitch, it's not recommended for use with weight distribution systems. As I have seen many Tesla owners towing RV's, I'm seeking advice on whether I really need a weight distribution hitch or can I use the Reese Towpower 21536RAK 2" Drop Standard Class III Starter Kit? Any help regarding this matter would be greatly appreciated.

We used a weight distribution hitch with our trailer as well... no issues at all. Performed great.

 

[doghousePVD]

I put on the after-market drawbar and weight distribution hitch on my X. Towing a 3000 lb Safari Condo. Maybe overkill but works great. Have towed about 15,000 miles so far.

 

[ecarfan]

I put on the after-market drawbar and weight distribution hitch on my X. Towing a 3000 lb Safari Condo. Maybe overkill but works great. Have towed about 15,000 miles so far.

What aftermarket hitch are you using?

Are you towing the Alto F2414?

Nothing wrong with using a weight distribution hitch even if technically you don’t need it, but at that weight your trailer is over 50% of your X so I think you made the right choice.

 

[doghousePVD]

Towing an A2124.

Safari Condo said they required a weight distribution hitch and I didn’t think the stock hitch and ball was adequate. Probably a bit of overkill, but one less thing to worry about.