by tzs | 2025-07-24 07:37:03+00:00
Yup. For example on a round trip today in me EV (2025 Hyundai Kona) on the out here are the stats:

2 kWh for the drivetrain 809 Wh regenerated

On the way home:

2 kWh for the drivetrain 547 Wh regenerated

For the round trip that's 33% less energy use than if the car did not have regenerative braking.

I'm mostly happy about that but there is one thing that annoys me. 33% is close to how much a kilometer is shorter than a mile (38%).

Why the fuck would I care that these two numbers are that close? It is because of a mystery in the Hyundai app. When you look up the trip details for an EV trip it gives you mileage, duration, and energy use (drivetrain, climate, accessories) and regeneration.

The mileage is substantially less than what the car shows. For example for the aforementioned trip home that trip odometer shows 8.0 miles but the Hyundai app shows 5 miles. The car odometer has the correct distance.

There are two theories to explain this.

1. The app is showing how many miles worth of energy you used rather than your actual trip mileage. All the other data it shows (except for the duration) is energy related. For my 8.0 mile trip I got 3 miles worth of the energy the drivetrain used back via regeneration, so I only actually paid for 5 miles worth of electricity.

Based on the Wh given it should actually be 5.4 miles, but the app only displays integer mileage so 5 it is.

2. It's a botched unit conversion. E.g., the car uploads the data in miles but the expects the data to be in km, so it is doing a conversion. That would turn the 8.0 into 5.0, which would be 5 in the app and so matches what theory #1 predicts.

I've checked several of my trips and they have always happened to have the right amount of regeneration so that the two theories match due to the app only showing an integer mileage.

I did a test today to try to tell them apart. I changed the car's settings to km and took a trip. The idea was if the car had been uploading in miles that would hopefully change it to upload in km, matching the app's expectation, and so the miles shown in the app would match the actual miles of the trip if theory #2 was correct, and show the regeneration corrected miles if theory #1 was correct.

The result was that the app still showed miles consistent with theory #1. So mystery solved, right?

Maybe not. When the car was set to miles everything showed in miles. Speedometer, odometers, efficiency (mi/kWh), speed limits it read from traffic signs, and speed limits it gets from the map data when using navigation on highways.

I expected than when I switched it to km all of those would be in km, and I would not see miles anywhere. Also, I expected that when it saw a speed limit sign that said say 60 it would interpret that as 60 km/hr.

What actually happened is that miles mostly did go away, except on the speedometer it added a smaller mi/hr display under the km/hr display. For the traffic signs it still knew they were in mi/hr and it converted them, so when I got on the freeway as soon as I passed the sign that said 60 the speed limit sign shown on the instrument cluster said 97, and the red dot on the speedometer showing the current limit was placed in the right place.

That suggests that the car knows it is in a country that uses miles, and doesn't just go by whatever the units setting in the setup screen is set to. It could be that in miles countries the car also uploads in miles all the time, and so switching the units setting to km would not change the results if theory #2 was true.

Now my plan is to find a big parking lot that is mostly empty overnight, such at a Walmart or Home Depot or a mall, go there and turn the car off and then back on which starts a new trip, set regeneration to 0 which turns off automatic regeneration on the accelerator so the car only regenerates when you use the brake pedal, and then drive around the parking lot for about 10 miles without using the brakes, then coast to a stop and turn the car off the end the trip.

Then I'll turn it back on, drive home, and check the trip details in the app. If theory #1 is right then the miles in the app should match the odometer miles. If theory #2 is correct the app miles should still be 38% shorter than the odometer miles.