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Trailer vs. Bike Carrier

Discussion in 'Model X: Driving Dynamics' started by mknox, Jul 12, 2018.

  1. mknox

    mknox Well-Known Member

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    Can someone rationalize these two snippets from the Owners Manual?

    Why would a bike rack with a hitch weight over 120 lbs. cause "significant damage" whereas a trailer with a hitch load of 500 lbs. is okay? And for that matter, why would the trailer tongue weight rating be less if the car has 22" wheels?

    My car is Midnight Silver Metallic in case paint color makes some sort of difference!


    Snip 1.JPG Snip 2.JPG
     
  2. ecarfan

    ecarfan Well-Known Member

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    Yes, it’s all about the paint color. ;)
    My guess is that the bike rack loads the hitch in a different manner than a trailer tongue does.
    My guess is that 22” tires, with their shorter sidewalls, cannot safely handle as much downward force as 20” tires can.
     
  3. ctn531

    ctn531 Member

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    ecarfan is correct about the bike rack loading the hitch differently. First - the bike rack ... The bike rack is solely supported by the hitch with a fair amount of weight hanging off of it (up to 120 pounds). This weight not only produces a downward force on the hitch, but it also produces a substantial rotational force (torque) which the hitch is not designed to handle. The trailer is different because the trailer has wheels supporting most of the trailer weight. Because the trailer is supported (with the wheels), no rotational force is induced on the hitch.

    As for the wheels, my best guess is that there is more air (and sidewall height) in the 20" tires - this absorbs the bumps and road better than what the 22" wheel is capable of. The 22" tire (with less air and lower sidewall height) will "bottom out" easier & faster than the 20" tire.

    Hope that helps ...
     
  4. roblab

    roblab Active Member

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    I use the trailer hooked to my Model S -- to haul everything that won't fit in the car (bikes do). It has a tongue weight of maybe twenty pounds. I would never tow anything with a 500 lb tongue weight on my hitch. Rent a truck. Some things are just common sense.
     
  5. mknox

    mknox Well-Known Member

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    I figured a 4,900 lb. trailer with a 500 lb. tongue weight bopping down the highway tugging and bouncing away would put more stress on the hitch and vehicle sub-frame than a couple of bicycles. When you corner with a trailer, you can put substantial rotational force on a hitch too.

    But after I posted, I was wondering this: Could it be an error in the Owners Manual? Originally, the Model X could be ordered with just a receiver for bike/ski racks (no trailer towing) and separately could be configured with the full blown trailer tow package. I wonder if the 120 lb. bike load limit is based on that old-style non-towing receiver? Now all Model X vehicles come with the full tow package and perhaps they just didn't change the language in that section?

    And yeah, the lower weight on the shorter sidewall 22" wheels makes sense. I was thinking only about the stress on the hitch and vehicle subframe.

    Not that I intend to, but the manual clearly states it is SAE Class III rated (4,960 lbs. trailer / 500 lbs. tongue) so "common sense" would suggest you could tow those kinds of loads. I was really thinking of one of those hitch mounted cargo trays where I might want to carry a generator, small outboard motor and such rather than have it stink up the interior of the car. Well below 500 lbs. but probably above 120.
     
  6. ewoodrick

    ewoodrick Member

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    Hold your hand straight out, add let's say 50 pounds. How hard is that to carry?
    Hold your hand straight out, put a rope pulling a cart with 300 pounds in it. How hard is that to carry?

    Tongue weight is very important when carrying trailers and I believe in general, the tongue weight is recommend to be about 10% of the trailer weight. The vertical forces that bikes represent turn into some pretty significant rotational forces on the mounting point. Also, if there is too much weight on the rear tongue, the car starts to ride badly, with front wheels in the air. Aside from all of the wear factors, this probably causes the safety features to get confused.
     
  7. Yinn

    Yinn Active Member

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    I think it's more accurate to say hold your hand straight out and hold 50 lbs. Then hold your hand straight out and pull a rope with 2000lbs on it, with 200lbs of it in your hand. But then that 200lbs is still 200lbs and a heck of a lot more than those 50lbs.

    I get the torquing from vertical forces if the carrier were to rise from the hithc point. It's the reason our hitches stipulate to stay with 0 drop and no more than .75" rise. But a hitch carrier with no rise (ie, cargo carriers) should have the same type of vertical loads as what tongue weight has. It's literally how tongue weight is measured, as a vertical load. What you won't have is torquing caused by a carrier going backwards as a trailer's pull will be horizontal (if properly leveled) but that should apply to a flat carrier as well.
     
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  8. ahkim

    ahkim Member

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    Great timing of this post. I've been using my Kuat NV 2 bike rack and just bought the +2 bike addon which allows me to have 4 bikes on the back. Problem is the rack is 80 lbs and 4 bikes close are nearly 120 lbs for a total of 200 lbs. Is it nuts to push it that far? How much do you think we could go over and still be "safe"?
     
  9. ctn531

    ctn531 Member

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    I've owned the +2 rack before but in the Thule version - the Kuat and Thule 4-bike configurations are HEAVY bike racks. As you point out, once you add bikes you are way over the 120 pound limit - but even if you were at the 120 pound limit, I would not suggest using the +2 because of the huge lever arm - the rotational forces are ridiculous. 200 pounds ... forget about it. Sorry, but my $.02.
     
  10. ai4px

    ai4px Member

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    Think moment of inertia and resonance. Buddy of mine took is camper to the beach with a really heavy duty 2" receiver hitch on the back and a bike rack. Really overloaded, 5 bikes (2 adults, 3 kids). He got into one of those rhythmic places on a concrete interstate and got a resonance going. Within a mile or two, the bike rack had ripped the 2" square tube off the bumper at the weld.

    A trailer is more likely to have shear forces straight in line, whereas a bike carrier is more likely to have torsional forces.
     
  11. mknox

    mknox Well-Known Member

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    That is certainly true, but I am not aware of any other auto maker or after-market hitch that actually advertises different tongue weights for trailers vs. bike racks. I have not done a thorough investigation, but know my former GMC Envoy made no such distinction. My buddy's Buick Enclave also with SAE Class III hitch is silent on this too. The fact that many bike racks capable of much heavier loads are readily available on the market also raises my suspicions.

    I still wonder if the language is a carry over from when Tesla offered a non-trailer towing hitch that was ONLY for bike racks, and maybe that hitch wasn't mechanically the same. This is not urgent for me as I have no immediate need, but had been considering one of those hitch mounted cargo racks and assume the same "bike rack" limitations, if indeed true, would apply to those things as well.
     
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  12. NORCAL-EV

    NORCAL-EV Member

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    Hello Fellow Tesla Model X Owners:

    I am a relatively new member of this forum having just picked up our 2018 Model X 100D in late March (after selling our diesel scandal ridden 2013 Audi Q7 TDI).

    I thought I would add to this thread as this topic has been on my mind months before deciding to move forward with our Model X purchase. Before I proceed please note that (in the image below) our Model X was at the Vacaville, CA Supercharger location and there were plenty of empty stalls available (16 total at this location). I would never block access to a Supercharger. This was our first official Supercharger session and it happened early on our first (I will admit anxiously awaited) Model X road trip from Los Gatos, CA to Sunriver, OR.

    Thule Rack with 4 Bikes - Model X.jpg Vacaville, CA SC location

    We successfully made the 515 mile trip with the below setup:

    -2 adults
    -2 kids
    -2 dogs
    -luggage for all (seemed like we had way more room for our luggage with the frunk and rear sunken cargo area compared to our 2013 Audi Q7 TDI).
    -Thule T2 Classic (2) Bike Platform Rack with extra (2) bike option (total 4 bike capacity). Total weight in 4 bike mode is 85 lbs.
    -4 bikes (approximate weight of each...conservative):
    • My fat tire DIY e-bike (66 lbs.)
    • My wife's Townie DIY e-bike (45 lbs.)
    • Daughter's Electra bike (40 lbs.)
    • Son's BMX bike (25 lbs.)
    • Total tongue weight including Thule rig is around 261 lbs.
    Before our trip I researched tongue weight information on this forum, discussed my setup and estimated 261 lbs. tongue weight with Tesla Service Center team (they stood by the 500 lbs. tongue weight specified for the 2" Bosal hitch), etc. To add more confidence to my decision we had the same setup on our Audi Q7 for the past 5 years with zero problems.

    I am writing this post from Sunriver, OR have made the journey with zero problems. I checked the rig multiple times (We stopped at 4 Superchargers on the way up here + I viewed rig via the fantastic Model X rear camera).

    Here is the rub...this Thule bike platform worked great but charging at a Supercharger without trailer stall option is an issue. We got lucky in Vacaville, CA. The Corning, CA SC had a trailer stall available, at the Mt. Shasta, CA SC (see image below) we were able to drive behind and charge (it looks like they are getting ready to remove this older 4 stall setup as they have a newer 16 stall set of Superchargers across the street...not sure if they have trailer stall at this new location). Our final SC session found us in Klamath Falls, OR and this location had a trailer stall option.
    Older Mt. Shasta SC Location.jpg Mt. Shasta (older) SC location


    LG to Sunriver - Google Map Directions.PNG
    Google Map Route Info

    The Tesla Model X is a tank...in a good way.

    :)
     
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  13. mknox

    mknox Well-Known Member

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    So, the plot thickens:

    I decided to bust out the hitch receiver and practice taking it in and out. BTW, I found it quite the PIA to do, but finally managed to get it on and off the car.

    But look at what's printed right on the receiver itself:

    20180728_192920661_iOS.jpg

    This also says that bike racks have reduced vertical loads, and that 2 is the maximum number of bikes.

    I did some further digging in the manual, and that language is not so clear on other cargo carriers (like the hitch mounted tray I am interested in). For other carriers, it just says to be conscious of the 500 lb. tongue weight and to follow the carrier manufacturer's instructions.

    As others have said, it must have something to do with the twisting force that a bike rack can put on the receiver. Still curious why this seems to be a Tesla-specific concern.
     
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  14. Yinn

    Yinn Active Member

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    That’s new, I posted in March 2017 and it didn’t have any mention of that. They probably got tired of people asking. Here’s the specific picture...no such sticker.
    [​IMG]

    I’d also venture to say this isn’t a Tesla issue, but rather a Bosal quick hitch issue. From what I’ve read the euro hitches on Audi’s/VWs that use the swan neck/quick connect also have the same restrictions. Some straight out lower the total capacity to the lower number instead of splitting it out
     
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  15. mknox

    mknox Well-Known Member

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    Same part number and everything... just the new bike capacity line. Very interesting.

    In reviewing some YouTube videos of European Model X's, it appears they use the "Swan Neck" style quick hitch as well. Not sure what the ball size is, but it is integrated into the device and can't be changed.

    Likely is a Bosal issue. I've also read where some Model X owners are swapping out the Tesla hitch with other third-party hitches that have the square receiver permanently welded on. Likely stronger, but you do have the permanent square tube sticking out at the back of the car.
     
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  16. Yinn

    Yinn Active Member

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    Yea I think this puts an end to it given the same number. Indicates nothing changed but the sticker. Doesn’t matter if you have the “accessory hitch” early part, late part, etc. official from Bosal and Tesla that the proper bike rack weight limit is 2bikes/121lbs and exceeding it would be at your own risk.

    Interestingly enough, Tesla’s own carrier holds 4 bikes. Given they specified bikes and not just wright, I do wonder if aero is a factor as well..
     
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  17. NORCAL-EV

    NORCAL-EV Member

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    Thank you for bringing this information to my attention. I will proceed with caution on the return leg and re-evaluate my hitch situation.
     
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  18. mknox

    mknox Well-Known Member

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    One final inconsistency I found in my quest for info on this hitch system. Tesla says that you cannot lower the ball platform at all, and only a 3/4" rise is permitted. Yet Tesla's own video instruction shows this which looks like a 3 to 4" drop.

    Video Capture.JPG
    20180728_192920661_iOS.jpg
     
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