So, I did a bit of research, and found that quite a few folks (especially in Europe) tow their caravans with their EV6. While I don’t have a caravan to tow, I did intend to get a trailer. So I studied trailers and I studied the towing limits of my EV6 and I found that with the tow capacity of 2,300 lbs, I should limit the weight of the actual trailer when empty. I found the Aluma 638BT to fit my needs, with an empty weight of only 400 lbs. All Aluminum construction, nothing to rust or rot, and maximizes my car’s carrying capacity. Pricey, but what isn’t? I picked it up yesterday, and paid close attention to my miles/kwh on the trip to Olympia, 4.2 M/kwh. Coming home, it fell to 2.7 M/kwh. Empty! No change in regen settings. Question: is that normal? What is your experience in mileage loss when towing? I did my testing over mostly flat roads, so I understand that elevation gains would make a huge difference.

I don’t have anything to tow, but wind resistance makes a massive difference in your efficiency. Were you driving at highway speeds? If so, that’s almost certainly where your losses came from.

kwame said:

I don’t have anything to tow, but wind resistance makes a massive difference in your efficiency. Were you driving at highway speeds? If so, that’s almost certainly where your losses came from.

Yes, averaged about 65mph both ways. I got the bifold rear ramp, to reduce drag…

@Kenneth

So, if you really feel like figuring out whether your losses are aerodynamic or tow weight, there’s a relatively simple way to do it: test at different speeds.

Get your energy readings while driving your car in a 40 mph zone, both with and without trailer. At 40mph, on a reasonably windless day, you’re not going to have a tone of aero losses, compared to 65mph.

Energy use is not linear. I was on the highway running really low, so I dropped from 65 to 57, and drafted behind a semi for 10 miles. That cut my energy usage almost exactly IN HALF. It wasn’t the speed reduction (mostly), but the drafting the semi. Using it as an aero boost basically was like driving with a strong tail wind.

@kwame

Indeed, wind resistance increases exponentially.

emma said:

@kwame

Indeed, wind resistance increases exponentially.

You sure it’s not quadratic?

Easy to verify if you look it up

Howard said:

emma said:

@kwame

Indeed, wind resistance increases exponentially.

You sure it’s not quadratic?

Easy to verify if you look it up

X^2 drag force increase isn’t exponential, 2^X is

@Howard

“At first glance, you would think that a 100-mph wind applies a load that doubles in magnitude in comparison to a 50-mph wind…and you would be wrong. This is a typical notion when speaking with the general public. However, wind speed and wind load have an exponential relationship, not a linear one.”

What Is the Relationship Between MPH and PSF? | EDT Engineers.

@emma

Right after that it says wind ^ 2

It’s a polynomial growth curve

Weird that so many people aren’t triggered by going from linear to exponential. Maybe it’s not hammered in properly to non-CS engineers.

Perhaps some corners of engineering consider polynomial growth exponential

And what would you classify 2^x as if you already used the exponential descriptor for a polynomial

And even if exponential is standard in some corners of English, quadratic is still accurate and more specific

@Howard

Drag FORCE increases with the square of velocity. But the POWER required to overcome the drag force increases with the cube of velocity.

@Howard

I suppose I would be using the term loosely as my expertise isn’t in mathematics (env degree went as far as statistics and economics mathwise) and the accuracy of my language won’t be as good as someone trained in a math heavy discipline.

@Kenneth

At an avg of 65mph I’m definitely not surprised. Try again and observe numbers at an avg of 45-55mph, should make a huge difference.

@Kenneth

When towing you need to drop down to more like 50-55mph if you want decent range

@Gabriel

Wait…the OEM trailer package has sensors for trailer weight?

Kenneth said:

@Gabriel

Wait…the OEM trailer package has sensors for trailer weight?

I’ve got the OEM trailer harness as well. Pretty sure there are no sensors for weight. How could there be? It’s just the wiring for brake, hazard and turn signals.

@Ronald

When I plug in my trailer, it puts the car in “trailer mode” and in the settings I can change the weight of the trailer between the four options I listed. Auto mode adjusts the range based on actual performance. The other three decrease the range based on the option the driver selects.

So in reality it doesn’t actually detect the weight sorry. It monitors the mileage in auto mode and changes the range in the guess o meter based on real world data.

This is with the Kia “active” harness, not just the standard harness.

@Gabriel

I have the same harness as you. Yeah, there are no sensors so it must use actual efficiency to update the GOM.

The single biggest factor in this is not weight but aerodynamics.

Here’s a fun experiment: drive for 20 minutes at highway speeds with your windows open. You’ll see a huge drop in efficiency. The car’s aerodynamics are incredible, but only if it’s exactly at intended.

With EV towing, the aero of the trailer is super important and very hard to do well.