Range in a Tesla

The available range in a Tesla is the forecast of how far the car can go before it runs out of electricity and is a question many owners get confused or frustrated by. It's rarely a consideration on a ICE as the available miles can be easily and quickly replaced at a fuel station, however when you are in an electric car the available range is more important to allow for planning if and when you need to stop to charge.

Tesla also do things differently to most other companies, but once you get to understand what the numbers represent, you can then decide whether you want to show miles or km, or prefer not to know and show %.

Energy consumption varies

It is impossible to know exactly how far a car will travel on a given amount of electricity, the best you can do is come up with an approximate for the range in miles or km. There are a number of reasons for this:

Because of the variability described above, the number Tesla display works in a completely different way. They take the EPA rating (the official energy consumption figures per mile from regulatory testing) and assume that a mile requires that much energy. The battery management system works out how many kwh of energy are available and converts that to miles using the official efficiency figure. The reason they do this is much the same as why a lift will say "max 8 people". The limit is not really driven my the number of people, it is the weight, and 7 very large may reach the weight limit and 9 or 10 children may be fine, the use of a number of people is simply because its easier to understand "8 people" than if the limit read "500kg" or "1200lbs". It's translating the real measurement into a form of units that is more relevant to the user, in a lift its the number of people and in the car it's how far it can drive.

Where it starts to become a little confusing is that over time and in different countries, the official tests have resulted in different efficiencies for for same car. The common ones are EPA, NEDC and WLTP depending where you are in the world and even when your car was made and they all differ to a greater or lesser extent, and depending on which is used you would get different results. Even petrol cars have this problem as miles per gallon vary in different countries because a US gallon is a different size to a UK gallon.

Depending on the age and model of the car one of the following will be used:

In summary, each of the methods above is just using a different figure to translate the available kwh into miles or km using a fixed ratio. Just like when getting in a lift you might make some mental adjustments for the size of people getting in with you, when driving you have to make some mental adjustments to know whether that range is achievable. Equally, if the car is showing 200 miles of range and you want to driver 30 miles, its simply not a concern just as two person getting into a lift for 8 people would not even consider the limit.

Other sources of range information

As said, the above figures are all based on a fixed approximation of how much energy is required to drive 1 mile. Tesla do have other energy screens that can provide different figures:

  • Projected Range

    Projected range

    The only place you can see a range based on recent driving behaviour is to display the energy screen and look for the projected range figure. This uses the average energy consumption over the length of the recent distance selected and uses this and the BMS reported available kwh to work out a range. There is also an option to show this on instantaneous consumption but this is of little benefit. This figure can fall rapidly in winter in cold weather due to the early parts of any journey being quite high on consumption, something thing that typically improves on a journey.

  • Trip estimate

    Projected range

    Using the same energy screens, if a trip is entered into the navigation then the car will calculate the consumption for the journey and track actual to estimated consumption and predict an arrival state of charge. It will also suggest charging or reducing speed if required. This is probably the most useful method if on a single long journey.

  • Economy

    Projected range

    In addition to the range figures, the car can show the economy of the car, this is typically the economy on the last journey, spanning short stops and the economy since last charged. It's worth knowing what your car used for Typical consumption as a mental reference against which you can compare, for instance a Model S is around 300 wh/m unless it's a performance which is nearer 330 wh/m. You can then mentally gauge whether you're exceeding this considerably or not.

  • Showing percentage

    One of the most hotly debated topics is whether you should show a range at all on the dash or just show a percentage. The argument is that as the range in miles is always wrong, don't display it, The counter argument is the percentage doesn't really tell you anything either, and at least a rough mileage is better than no mileage.

    We think many owners simply decide not to understand what the miles range represents and become frustrated with its apparent inaccuracy and so adopt %, others seem quite content knowing that the miles displayed is typically an over estimate but prefer the easy reference and buffer margin when doing a trip.

    We display range, we let the battery icon give us an indication of the fraction of how full, but there is no right or wrong.

    Degradation

    Batteries do lose some capacity over time and Tesla warrant new cars to retain 70% of their capacity at the end of 8 years or the miles limit (which varies by model). Those displaying % will simply not see any reduction in the available miles at a given state of charge. Those showing miles may see a reduction over time.

    There a few simply checks before you become too worried about degradation:

    Vampire drain

    One aspect of Tesla ownership that surprises some people is the car uses electricity even when not being driven. This is called Vampire drain. This can range from a few miles per day to quite significant amounts of energy that could deplete the battery within a week.

    Tesla Energy Saving option

    To reduce vampire the following steps are recommended

    • Only use Sentry Mode needed. This uses huge amounts of electricity for what it does and will deplete the battery in a few days if you are not careful
    • Uncheck the 'Always connected' option found a little oddly under the Display tab.
    • Turn off 3rd party applications that poll the car like teslafi, as this is preventing the car from entering deep sleep. This would have a similar effect to leaving always connected turned on
    • For the most aggressive form of energy saving, also turn on Energy Saving. The downside to this is the car can take longer to wake up when you get to the car, but if you were leaving the car for a few weeks, this is a good option
    • Lastly, do not open the Tesla app to check on the car. This causes the car to wake up again using energy.

    A combination of the above will minimise the vampire drain in the car and reduce the amount of battery loss over night or whenever you leave the car.

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