Weird twist to having an efficient design: An efficient EV will take a bigger apparent range hit when towing.
Momentarily, I'll ignore differences in how the aero of the lead vehicle affects the airflow around the trailer. With that in mind, then we can say pulling the trailer itself is always going to cost about the same in Wh/mile. So, a tow vehicle that uses fewer Wh/mile will take a bigger percentage hit to its range when towing.
Example:
- Big inefficient EV that gets 500 Wh/mile, and uses a 200 kWh pack to go 400 miles. Add on a trailer that requires an extra 350 Wh/mile, and the total cost to drive is 850 Wh/mile. Now, that 200 kWh pack is good for 235 miles, or 59% of the range without the trailer.
- Potential Cybertruck at 350 Wh/mile, would need a 140 kWh pack to do the same 400 miles. With the extra 350 Wh/mile trailer, the total cost to drive is 700 Wh/mile. Now, that 140 KWh battery is only good for 200 miles, or 50% of the no-trailer range.
- Just for fun: a theoretical Aptera at ~100 Wh/mile would need a 40 kWh pack to do the same 400 miles. With the extra 350 Wh/mile trailer, the total cost to drive is 450 Wh/mile. Now, that 40 kWh battery is only good for 89 miles, or 22% of the no-trailer range.
It potentially gets worse too:
If the terrible aerodynamic shape of the big inefficient truck effectively blocks some of the aero drag from reaching the trailer, then Wh/mile of the trailer might actually be lowered at speed. Likewise, if the Cybertruck's aero profile tapers down to a small wake behind the Cybertruck, then the trailer would not see any reduced drag. So the aero details that make a lead vehicle more or less efficient could further exaggerate the differences above...making the big inefficient truck look a bit better, and the Cybertruck look a bit worse.
An uninformed and/or devious journalist could easily present a biased towing range test that only measures the range loss of a bunch of EV's when a trailer is added. The more efficient EV would look "worse" because it loses more range....and the audience would only see this "problem" as long as the writer hid all of the actual Wh/mile numbers and didn't bother to explain the physics behind the results.