Range for Speed 2

In the previous post “Range for Speed” it was explained that high speeds dramatically decreases range. If you want to travel far, it is advisable to reduce speed. The post became a blockbuster and is now followed up with episode two (Range for Speed 2) to answer questions about consumption in low speed.

The first post tested differences in consumption between 80, 100 and 120 km/h. The tests were done on the same stretch of road with the same wind, temperature, etc. The car was on cruise control in all tests. It turned out that the power consumption increased 25 % when the speed increased from 80 km/h to 100 km/h and in 120 km/h it was more than 50 % higher.

In Part 2 of the test, we have now examined the difference in consumption between 40, 60 and 80 km/h. Also this time the conditions were the same and the car was running with cruise control at the specified speeds. The results show that even at low speeds the difference in consumption is significant. The car consumes 15 % more energy at 60 km/h compared to 40 km/h. At 80 km/h the consumption has increased by 40 % compared to the 40 km/h.

For practical and safety reasons it was difficult to test the low speeds on the same road as the high speeds. However, since the consumption at 80 km/h was almost identical in the two tests I have paired the data series. From this we can conclude that consumption is 120% higher at 120 km/h compared to 40 km/h!

Power Consumption at different Speed

The figures become very tangible when converted to range. If we assume that it is possible to travel 100 km at 100 km/h (given a certain temperature, wind, road conditions, etc), it should be possible to go 25 km further if speed is reduced to 80 km/h. At 60 km/h it will be possible to go 155 km and at 40 km/h all 180 km.

Range at different Speed

The range for speed relationships is found to be almost linear and flattens out only very marginally at low speeds. It can therefore be concluded that if you want to beat a range record with your i3 you should drive as slow as possible. However, if you need to travel far and want to arrive quickly, it is certainly a better strategy to drive fast and take a 20 minutes pause by a rapid charger.

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14 thoughts on “Range for Speed 2

  1. Having driven my i3 for the last 4 weeks, your findings are absolutely true.

    This vehicle is best at speeds under 90km.

    The Eco Pro Plus is far more effective than I realized, especially in highway stop & go traffic.

    Leaving in comfort mode, I could’nt believe how quickly the charge disappears.

    If your willing to work with the settings, on going, what a huge difference.

    Love my car, was expecting better range overall. Learning curve like anything else.

    1. What was the test distance here? I’ve driven mine i3 from south of Norway up into the mountains E6/E16 and from mine experience i3 has much lower consumption over longer distances. Some examples:
      70 km distance at +90 km/h -> 12.5kW/100km
      100 km distance at 70-80km/h -> 13.3kW/100km
      70 km distance at +100 km/h -> 15.8kW/100km

      1. Additional comment to the low 12.5 kW/100km consumption:
        The 90km/h distance: flat highway
        The 70-80 km/h distance: a lot of up/down hills

        1. Hi Geir,
          It is important to underline that this was never an attempt to measure consumption or range. It will be very different depending on road, temperature, etc. The only thing measured was the difference in consumption at different speeds.

  2. Hi,

    I just bought an BMW i3 (waiting for it by the end of may) and after I discovered your page and I became quite curious because you mention this – as far I can unserstand:
    40 km/h – 10kwh instant consumption => 100km x 10kwh /40kmh = 25kw to make 100km?
    120km/h – 23kwh instant consumption => 100km x 23kwh/120knh = 19kw to make 100km?

    Or you drive for 100km and the total consumption at 40kmh was 10kw? meaning an instant consuption of 10 kw / (100km /40kmh) = 4kwh?

  3. I travel to and from work 100km each direction everyday. And 80 of them is at 110km/h.
    I use about 17.8-18.5Kwh at this speed. In comfort and with very cold i have to REX 5min.

    But normally i reach work at 7-10% charge left. And since it cant fully charge during a whole day on 230 charger i leave at 95% and most days reach home at 6% with REX autostarted. Since i travel highway that much i dont regenerate any energy at all wich impedes distance.

    Nowdays i dont do 140 on our 110 roads like ive done the last 20 years before….. 😉

      1. I was using about 0.5 litres/day
        After update of software in car i dont Rex anymore except when weather is very cold. When i wrote post i had only had car for 2 months, but now after another 14months i learned alot and drive mostly in Eco-Pro mode. This gives about 25 more kilometres. Commfort mode i use when i drive locally or want to drive a bit “manly”….

        Done 51000Km in the car now. I love every minut in it and will NEVER NEVER go back to a fossil car.

        As an added bonus here on the west coast in Sweden many municipalitys have a free rapid recharger available.

        I calculate my use of gasoline so far is about 250litres.(0.6l/10km) Mostly used on long distance travelling during vacations.
        Something i have noticed when i meet leaf owners and Zoe owners on charging stations is the fact i recharge my battery from 5% while they usually have about 20-30% charge in batterys when they charge it.
        REX is a big winner for sure.

        1. Thanks, very, very interesting !!! So, even in Comfort mode, you can expect 15 to 20 km per liter of extra range, quite impressive !

  4. If consumption is, indeed, proportional to speed, there is an interesting mathematical consequence.
    For a fast journey, drive for half the time and charge for half the time.
    This assumes there is no initial charge (or the journey is long) and no speed limit.

      1. Yes, I noticed that after I posted.
        You are talking about a practical problem using rapid chargers as they actually work, and doing a thorough job.
        I am talking about a theoretical observation, which may provide some insight.
        (I am also assuming that chargers charge at constant rates, which they don’t.)
        Here in Ontario there are very few rapid chargers. So the quickest way to get a long way might be to drive at 60 kph, maybe on back roads to be safer.

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