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Trailer Specs - Towing Safely

Discussion in 'Model X: Driving Dynamics' started by Yinn, May 30, 2017.

  1. Yinn

    Yinn Member

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    I'm in the process of finding a trailer so I can tow with the Model X, this has become especially important to me as the 2nd row seats don't fold and I'm finding I need to tow more and more. Most of my towing is around town towing for utility and not for distance.

    So far the hunt has been challenging due to the restrictive specs from the Bosal/Tesla combination.
    [​IMG]

    While I did manage to find a straight ball mount that's less than 8" length (Harbor Freight), most are longer than 8" The 2nd issue is that the MX sits 15.5" to the top of the ball (maximum of 16.25" w/ .75" rise)
    [​IMG]

    The maximum trailer coupler height (bottom of coupler) then is around 14.75" and I'm finding a lot of trailers are higher - typically around 17-20" The one I am looking at (FREE SHIPPING — Ultra-Tow 4ft. x 8ft. Folding Aluminum Utility Trailer Kit — 1170-Lb. Load Capacity | Trailers| Northern Tool + Equipment) is 17.8"

    How is everyone making up the difference?

    I started reading about adjustable couplers, but wouldn't that be the same effect as using a riser on the ball mount? The other option is to rip out the axle and replace it with a drop axle to lower the height, but I might as well built my own trailer from scratch at that point.
     
  2. CmdrThor

    CmdrThor Active Member

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    I felt having a level trailer was more important than adhering to the restrictive specifications of the Bosal hitch receiver.
     
  3. SabrToothSqrl

    SabrToothSqrl Active Member

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    Ya'll worry to much. Are you hauling over 5k? No? Then hitch up and drive on.
     
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  4. loganintx

    loganintx Member

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  5. vandacca

    vandacca ReActive Member

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    Technically, you should only load the hitch to 120lbs (including the Cargo Carrier). Therefore, if you Cargo Carrier weighs 70lbs, you can only put an additional 50lbs in it, which isn't much.
     
  6. Phil Seastrand

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    Why do you say this? If the tongue weight limit is 500 lbs, why can't I load up to that much on the carrier?
     
  7. Yinn

    Yinn Member

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    That's what I used to think, I can tow on other cars by simply adding a hitch and adhering to the hitch limits. But a $500 repair bill for a broken item due to "excessive weight/improper towing" changed my mind.

    Model X Owner's Manual: Supported Accessory Carriers
    To support the installation of an accessory carrier (such as a bicycle, ski, or snowboard rack) on the rear of Model X, the accessory hitch or optional towing package is required. Do not attempt to install an accessory carrier on a Model X that is not equipped with the accessory hitch or towing package. Doing so can cause damage

    Model X is designed to support an accessory carrier of up to 120 lbs (55 kg). When carrying accessories on Model X, always check to ensure that the maximum weight is not exceeded. For example, this weight threshold is sufficient for carrying two bicycles weighing approximately 40 lbs (18 kg) each, or four bicycles weighing approximately 20 lbs (9 kg) each, assuming the accessory carrier weighs approximately 33 lbs (15 kg)


    It doesn't distinguish between the tow package and the accessory hitch for the weight limit. My guess is that the carrier is essentially the same as a rising ball mount. The higher it goes, the more leverage there is for the load, causing excessive force on the hitch. It essentially acts as a pry bar against the rear bumper/mounting points of the hitch. So the larger the lever, the less force/weight can be carried or exerted.
     
  8. vandacca

    vandacca ReActive Member

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    Yes, exactly what @Yinn wrote. However, I suspect that the manual may not be completely accurate, as the warning right after the quoted information above has the following warning:
    So, while the hitch limit is only 120lbs, that was probably for the originally designed 1.25" accessory hitch and not for the 2" tow package (it's probably the higher 500lbs). But until we have an updated manual from Tesla, we're only guessing.
     
  9. Yinn

    Yinn Member

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    I thought that as well, but then I noticed it distinguishes the difference between an accessory hitch - 1.25" reciever that doesn't exist anyway, and an accessory carrier.

    Under the accessory carrier it says it can be used on the accessory hitch or towing package before going into the limits.
     
  10. vandacca

    vandacca ReActive Member

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    I agree, this is clear as mud. :) IMO, referencing the 1.25" accessory hitch comprimes the whole section in the manual. I don't think we can trust it.
     
  11. mongo

    mongo Member

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    It's a matter of where the force is located. The hitch spec is a maximum of 8 inches from the receiver pin. Eyeballing from the X manual, the pin to vehicle attachment point is about 6 inches, so the net torque is 500 pounds at 14 inches, or ~580 lb-ft.

    The carrier platform appears to start ~13inches from the pin. The platform is 24 inches, so if the load is centered, the total lever arm is 6+13+12 = 31 inches. 580lb-ft/31in = 224 pounds to produce the same torque. The carrier is 70 pounds, so the maximum load to match the same static loading would be 154 pounds.

    Dynamic loading is much worse when using a carrier. A trailer only produces a force at the hitch ball, but the entire length of the carrier acts on the hitch attachment (think crowbar).
     
  12. Yinn

    Yinn Member

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    You lost me at 6 inches.

    Are you saying that carrier should be able to carry 154lbs?
     
  13. mongo

    mongo Member

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    Hi,

    First off, I would not use a carrier with the X, the 145 number was just the amount of weight that was equivalent to a fully loaded trailer when stationary. As soon as driving/ road dynamics occur, the carrier will exert much more force on the hitch than a trailer would.

    By way of illustration, image you have a sledge hammer. If you hold the handle and let it hang vertically with your hand next to your body, it is fairly easy to hold. If you extend you arm, it is harder to support (arm is doing more work). This represents the 8 inch hitch limit.
    Now, try to hold the sledge hammer horizontally from the end of the handle. Unless you have wrists of fury, it's not going to happen. This represents a cargo carrier attached to the hitch receiver. In all three cases, you are working with the same weight, but depending how it is applied, it takes more force to support.

    This is also why Tesla specifies the vertical position of the trailer ball. It minimizes the bending/ torque forces on the hitch attachment by keeping the structure and the force vectors aligned. If the ball were below the receiver, the 5,000 pound trailer would be trying to bend the hitch attachment under the car.
     
  14. CmdrThor

    CmdrThor Active Member

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    Someone should measure the ball mount Tesla uses to tow their Airstream mobile design studio. I am willing to bet the rise is more than 0.75". Of course they don't actually tow the Airstream around the country they just load the whole thing up on a trailer and tow that around with a big truck.
     
  15. idoco

    idoco Member

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    Based on this picture it looks to be an adjustable hitch. And just eyeballing looks to be at least 3-4" rise from the top of the hitch receiver!

    https://www.psfk.com/wp-content/uploads/2016/09/Tesla_Airstream_Mobile_Design_Studio_1.jpg
     
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