UPDATE: Tesla Model Y Towing |20-In Wheels Don't Reduce Weight Capacity
Tesla has officially launched its Model Y aftermarket towing package and cleared up the capacity discrepancy.
EDITOR'S UPDATE: Tesla has updated the language on its product page for the Tesla Model Y tow package. It's now clear that it can tow the same 3,500 pounds regardless of wheel size. According to Tesla, it reads:
"Equip your Model Y with a high-strength steel tow bar and 2” hitch receiver capable of towing up to 3,500 pounds on all wheel configurations."
The Tesla Model Y story has been interesting as far as towing is concerned. It was supposed to be able to tow, then it arrived and was seemingly unable to tow. There was nothing in the manual about towing. Shortly thereafter, it was rated to tow, and the option appeared online. If you chose ahead of time, you could have your Model Y prepped with the tow package before taking delivery.
Now, Tesla has launched its official aftermarket towing package. So, if you already have a Model Y, you can get the package and have the crossover readied for towing by visiting a Tesla Service Center. As Tesla previously stated, the Model Y can tow up to 3,500 pounds. However, if your Y has Tesla's 20-inch wheel option, it's only rated to tow 2,300 pounds.
According to Tesla's website, the towing package costs $1,200. It's not very easy to find on the website, but you can access it by clicking here.
As you can see, the information related to the capacities is listed. However, if you're ordering a new Model Y and adding the tow hitch before delivery, you may not see this information. On the Model Y order page, it just says the crossover can tow up to 3,500 pounds.
There is also information about trailer towing in the Model Y owner's manual on page 72. It is as follows:

We still have some questions related to all of this. Why does it tow less with 20-inch wheels than with 21s? What if you have aftermarket wheels on your Model Y?
Clearly, it all comes down to the wheels themselves and how they're rated. Be sure to do your homework if you plan on towing with the Model Y.
Source: Tesla via Electrek, via Drive Tesla Canada
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