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:

• Warm weather, downhill, steady 50mph or 80km/h driving and efficiency will mean efficiency is good and less stored electricity is required to cover a given distance.
• Cold weather, rain, uphill, high speed driving and the consumption will be higher and consequently range lower.
• In even moderately cold weather the first part of the journey can use much more energy than the later part of the journey meaning one long journey is more efficient that several shorter journeys even when the total distance travelled is the same. This is because the battery and car will need to use energy to warm up.
• You could mitigate some of that heating by preheating or preconditioning the car before departing. The energy use in the car is still higher but replenished from the charge point.
• Not all energy consumption is captured by the car, the car needs to be awake, so charging while locked and even preheating may not be recorded in the car.
• Some use the recent past energy consumption as a guide for future energy consumption, but the circumstances may not be the same, the car may have been warm when the past average was taken and the cold when you start driving etc which will result in an incorrect prediction.
• Unlike a petrol car, the variability in consumption can be very significant, driving a cold car in winter can result in 2 or 3 times the energy consumption as the same car when warm in winter. A petrol car, the consumption figures rarely vary for environmental factors and vary more for how hard the car is being driven.

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:

• Rated Range

  

  The Rated range is based on the testing standards in the US. The figure will vary by model as the efficiency varies, the Performance MX on 22" wheels being the worst with a Model 3 on 18" Aero wheels being the best.

  One source of confusion is the published figures in some countries uses the WLTP testing cycle, but the car displays the range using the US/EPA figures which are slightly different. As a result it appears the car can not do the same range, whereas in reality there is no difference in the available energy. In effect its like one country saying 8 medium weight people and another country saying 7 heavier people - the actual capacity is exactly the same.

  On earlier cars, the rated figure would often be the NEDC rating which was unrealistic and should be best avoided.

• Typical Range

  

  When the NEDC figures were being used for the Rated range, this was so inaccurate Tesla added a typical range option. This is virtually identical to the Rated range in concept, except the figure is more realistic. Typical is fairly close to the official EPA figures.

  To change between Typical and Rated, you select which you prefer in menu, although increasingly cars now only show the rated range.

• Ideal Range

  

  This one is used less today and was a version of the range when driven in Ideal conditions, thought to be around 50mph. As battery sizes have increased in general, the need to know the maximum you could eek out of a car has become less important. It is totally unrealistic.

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

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

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

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:

• If in Europe and other regions, the car will not be displaying range based on the same testing standard but the slightly more pessimistic US figure. As a result, the car may appear to only have about 95% of the range compared to the published figure. This is not a problem.
• If you have a Model 3 or Model Y and apply the Always Be Charging mantra, then the car may have drifted out of calibration and require a few simple steps to help it improve accuracy. Our guide to BMS calibration provides the steps you need to take.

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.

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.