Unless you are a vehicle aerodynamic expert (if so please cite your qualification, thank you) I am not sure if the larger size of the X means a useful gain in range because it "pushes more air out of the way" compared to the smaller size of the Model 3 which means it uses less wH/mi compared to the X and therefore might overall use about the same wH/mi when towing compared to an X. I am not a vehicle aerodynamic expert so I really don't know.
Well I suppose I do know a little about aerodynamics, but the concept is not really that complicated. It all comes down to the size of the wake created by the tow vehicle. Let me illustrate the concept with approximate but somewhat plausible numbers. All of this is simplified and assumes a steady-state cruise, no winds, flat ground, same trailer, etc.
Let's assume a trailer needs 200 Wh/mi to overcome tire rolling resistance and, if the trailer were magically rolling along with no tow vehicle, needs 800 Wh/mi to overcome aerodynamic drag. Therefore, the total energy usage to move
only the incredibly aero inefficient trailer is 1000 Wh/mi.
Case 1
Truck by itself uses 2000 Wh/mi
Truck pulling trailer uses 2300 Wh/mi
Difference due to trailer:
300 Wh/mi [=2300-2000]
Truck wake saves 700 Wh/mi [=1000-300]
Impact to Truck energy usage: 1.15x [=2300/2000]
Impact to Truck range:
13% loss [=1-1/1.15]
Case 2
Model X by itself uses 350 Wh/mi
Model X pulling trailer uses 700 Wh/mi
Difference due to trailer:
350 Wh/mi [=700-350]
Model X wake saves: 650 Wh/mi [=1000-350]
Impact to Model X energy usage: 2x [=700/350]
Impact to Model X range:
50% loss [=1-1/2]
Case 3
Model 3 by itself uses 200 Wh/mi
Model 3 pulling trailer uses 600 Wh/mi
Difference due to trailer:
400 Wh/mi [=600-200]
Model 3 wake saves: 600 Wh/mi [1000-400]
Impact to Model 3 energy usage: 3x [=600/200]
Impact to Model 3 range:
67% loss [=1-1/3]
In all cases, the tow vehicle significantly reduces the aero drag on the trailer. The tow vehicle saves between 600 and 700 Wh/mi that would be needed to move the trailer just by itself. This savings is due to wake from the tow vehicle. But the point here is that more efficient tow vehicles have a smaller wake and so
the smaller wake vehicles need to expend more energy to tow the trailer. The energy usage grows from 300 Wh/mi to 400 Wh/mi.
(This is very similar to how an EV needs to expend more energy to heat the cabin verses an ICE vehicle. The ICE vehicle normally has excess heat energy that can be redirected to the cabin but an EV needs to pull that energy from the battery. In the towing case, the truck is wasting energy creating it's wake and when towing is able to use that otherwise wasted energy to reduce the energy needed to tow. An aero efficient EV needs to use more battery energy to tow because it has a smaller wake.)
The other effect to recognize is that
the smaller wake vehicles lose a much higher percentage of their range. This is because the energy to tow the trailer is higher relative to the vehicle traveling only by itself. The range loss grows from 13% to 67% in these three cases.
We shouldn't quibble about the numbers used here as they're for explanation purposes only. In fact, the results are probably exaggerated using these numbers, but the overarching effects are real.
To take it back up a level...since the Model 3 will be a very aero efficient highway cruiser, using it to tow an aero inefficient trailer will have significant impact on range. To minimize this impact,
place a high priority on choosing a trailer that has 1) good aero efficiency and 2) minimizes being outside the wake of the Model 3.
One final note about the size of the wake behind the Model 3. The Model 3 is 56.5" high and 74.2" wide. If we ignore a couple of things, like that the smooth roof line pulls the wake down, we can multiply these two dimensions to have a reference wake area of 4,192 sq in. A short pop-up trailer, such as Chalet Classic at 66" high and 82" wide [5,412 sq in], has a frontal area 29% larger than the Model 3 wake. The Chalet XL, mentioned previously in this thread, is 73" high and 87" wide [6,351 sq in] and has a frontal area 52% larger than the Model 3 wake. (
PDF Brochure) So even the smallest travel trailers will significantly reduce aero efficiency and range.