Range for speed

There are many discussions on what accessories to select to keep power consumption to a minimum (and boost range). LED, heat pump, chargers…  Sorry to disappoint all speed lovers, but keep your right foot light on the pedal if you want range.

To understand the relationship between speed and power consumption I drove the same highway back and forth a few times in different speeds. The car was preheated and had gone 20 km to reach the test stretch so the conditions were about the same. The test was done with all speeds in both directions so wind and hills should be about the same. The car was put on cruise control in all tests.

In 80 km/h (50 mph) the average power consumption was 14.8 kWh / 100 km on the test stretch. When the speed was increased to 100 km/h (62 mph) the power consumption increased to 18.5 kWh / 100 km. Finally a speed of 120 km/h (74 mph) was tested under the same conditions and the power consumption then increased to 22.7 kWh / 100 km. While power consumption of course is influenced by conditions like temperature, road conditions, etc the take away from this experience is the difference in power consumption given different speeds. While not entirely scientific because of few data points the conclusion from my little test was that the power consumption is 25% higher in 100 km/h compared to 80 km/h. In 120 km/h it is 53% higher!

Power Consumption at different Speed

To put this in a way that is easier to understand. Let’s assume there is power left in the car to take you 100 km if you cruise at 120 km/h. If the speed is reduced to 100 km/h the range is increased with 23 km and if it is further reduced to 80 km/h the range will be 153 km.

Range at different Speed

It should be underlined that range has never been an issue in my daily commuting and I find range anxiety grossly exaggerated in media. But if you have to travel far and charge stations are scarce, then these statistics are good to keep in mind.

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11 thoughts on “Range for speed

  1. Interesting figures! It would be fun to have the same comparison with a 120d and 120i. I currently have an 120i convertible and its best cruising speed is about 80kmh. If i drive 120kmh, its quite thirsty. I previously owned a 320d and on the diesels, the speed dosent matter as much as the i3 and 120i.

    But to summarize this, it seems like electric cars suffer most from going fast (due to the gear ratio i guess..), and petrol cars next and the “winner” is the diesel. But, as the electic cars cost so much less to “refuel” they still are the clear winner in my point of view! 😀

    1. Hi Alex,

      Had the same discussion with a friend today about what the figures look like for petrol and diesel cars. I think your conclusions are correct and that lack of gears makes a difference.
      Surely the electric car is the winner due to low milage cost, but if you need range then these figures are not so good. And when you travel far it is often in a hurry and in high speed – it will cost many stops to recharge…

      1. Yes, agree. The only option then is the Tesla Model S P85. When the battery is drained, you would have covered such a big distance so a 30min break for charging 80% battery would do the trick.

  2. Hello,
    are those power consumptions the DC flowing from the battery or the actual AC kWh used from the grid ?

  3. Thanks, an other question : which part of that 22 kWh i3 battery is actually charged (usually, a small part of it is used as buffer) and how many kWh does it take to fully charge the battery (i.e. including charging losses) ?

  4. Hi!

    Fråga om räckvidd, vad kör ni som mest med era i3:or? Bmw “lovar” 11 mil, är det vad jag ska räkna med om jag köper en utan Rex? Funderar tex att köra sthlm city till Västerås ibland och då är det lite på gränsen. Hälsningar Erik

    1. Hi Erik
      I have done Stockholm – Västerås a few times now and it has never been a problem. The first time I was driving 90 km/h just in case but the last few times it has been 110 – 120 without any problems. Last time, however, I arrived in Västerås only to discover that the only public rapid charger in town, a crappy one from Fortum, was not working. After some thinking I drove down to the ABB HQ and asked politely to ask theirs. They were very kind and helped a BEV owner in despair. I believe Fortum is changing all of the bad chargers to a better brand.

      1. Hi!

        Thanks for the response. How important is the fast charger option for the bev? Pretty important I would guess?

        Kind regards,
        Erik

        1. I would say yes. If you have a BEV without the fast charger option (4U8/4U7) your action radius will be limited to just over 50 km (assuming you will need to go back the same distance before you start a slow charge). With the fast charger option you have flexibility to drive much further away. There is plenty of info about chargers in the posts “Standard charger enough at home“, “Lack of rapid chargers slows down car sales “, and “Rapid charger effect “. Please also read the comments 🙂

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