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Why Don't Ball Mounts with Longer Shanks Reduce Towing Capacity

Question:

Is there any sort of de-rating or calculations that need to be done when choosing drawbars? I just bought a 9-9/16 long 5rise drawbar since a shorter drawbar would have been ~1/2 inch from my license plate but saw even longer ones available. Then engineer in me feels like there has to be some de rating for longer drawbars. For an extra long draw bars there would be more torque on the receiver per pound of tongue weight so how could a hitch rating be the same for a short drawbar vs long? Ive previously bent the trunk floor with a hitch mounted motorcycle carrier and would prefer to not do that to my current cars. Question should be irrelevant of car but drawbar was bought for a 2016 Mazda MX-5 Miata with a hitch not sold through etrailer, it may also be used with a 2015 Toyota Prius C for small trips to the hardware store down the road if the hitch height is about the same and it fits.

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Expert Reply:

When looking at the weight capacities on ball mounts that feature a longer shank, such as the Curt Class I Drawbar # C45024 that you recently purchased, you can comfortably follow its listed weight rating without having to reduce the capacity based on its length beyond the hitch receiver. I definitely understand your concern with this type of design, as the further out from the vehicle you get, the more leverage any tongue weight will be putting on the trailer hitch.

This is definitely a potential issue when dealing with hitch-mounted accessories like a motorcycle carrier that you have used in the past, as the carrier doesn't have any support other than the hitch it is attached to, so this added leverage from a longer shank or extender will put a lot of stress on the hitch because it will be bouncing up and down during travel. This is why most hitch adapters, such as the Curt Extender # C45791, will actually reduce the trailer hitch's tongue weight capacity by 50 percent.

This same type of leverage and movement though is not the same for towing applications, as a trailer will certainly provide tongue weight, but most of the effort in towing is pulling a load, not carrying it. With this in mind, the tongue weight on a ball mount from a trailer will not be producing the kind of bounce and leverage that a hitch-mounted accessory would. For this reason, a longer ball mount shank does not require you to lower its or the hitch's capacity in any way beyond their listed ratings. The Curt Class I Drawbar # C45024 features a 2,000 pound towing and 200 pound tongue weight capacity, and as long as your tow vehicle and hitch do not have a lower capacity than this, you are perfectly safe towing up to its limit.

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Chris R

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