Why does my electric car lose range so much faster on the motorway?
Why an EV is the opposite of a petrol car, how much difference ten miles an hour actually makes, and how to plan a long journey around it rather than being surprised by it.
- Difficulty
- beginner
- Time
- 12 min
- Read
- 5 min
Short answer
An electric car is most efficient in town and least efficient at speed — the exact opposite of a petrol car. Aerodynamic drag rises with the square of speed and the power needed to overcome it with the cube, so the last few miles an hour cost disproportionately. There is no idling and no cold-engine penalty to offset it, and regeneration recovers nothing on a motorway because you rarely slow down. Dropping from 75 to 65 mph buys a meaningful chunk of range.
Drivers coming from petrol and diesel arrive with a mental model that is precisely inverted. A combustion engine is horribly inefficient in stop-start traffic, where it idles, runs cold and throws energy away as heat every time you brake, and comparatively efficient at a steady cruise. An electric motor has none of those losses: it uses nothing when stationary, is efficient across almost its whole range, and recovers energy when slowing. So the town figure is excellent. What remains at motorway speed is pure aerodynamics, and aerodynamics is unforgiving — which is why the official range figure, weighted towards mixed driving, feels wrong on the first long trip.
Step by step
- Understand where the energy goes at speed.Drag force rises with the square of speed and the power needed to overcome it rises with the cube. That is why the difference between 60 and 70 mph is far larger than the difference between 30 and 40. On a motorway, drag is where nearly all of your energy goes.
- Try 65 rather than 70 and watch the consumption figure.The car's energy display, usually in miles per kilowatt-hour or watt-hours per mile, responds immediately. Most drivers are surprised by how much a small speed reduction improves it, and it costs only a few minutes over a long journey.
- Accept that regeneration does almost nothing here.Regenerative braking recovers energy when you slow down, and on a motorway you barely do. All the efficiency benefit of an EV in traffic is unavailable at a steady 70, which is why the gap between the town figure and the motorway figure is so wide.
- Take the roof bars off.Roof bars, a roof box or bikes add a large amount of drag exactly where it costs most. On an EV the effect on range is dramatic — often far more than the equivalent fuel penalty on a petrol car, because there is less total energy to start with.
- Watch the heating rather than the driving.In winter the cabin heater is a substantial draw, and unlike a petrol car there is no waste engine heat to use. Heated seats and a heated steering wheel warm a person for a fraction of the energy of warming a whole cabin, and most cars let you drop the cabin temperature once the seats are on.
- Use the car's own route planner.The built-in planner knows the battery's state and temperature, the route's gradients and the charger network, and it will precondition the battery before a stop. Third-party apps are useful for choosing where to stop; the car is usually better at predicting whether you will get there.
- Plan around the charging curve, not around range anxiety.The fastest long journey is generally short frequent stops at a low state of charge rather than one long stop to full. Arriving at a charger with fifteen per cent left is efficient use of the curve, not cutting it fine — provided there is a backup charger in reach.
- Expect a headwind and cold rain to hurt.A strong headwind adds directly to the drag, and cold dense air is harder to push through than warm air. Combine that with a cold battery and a heater running, and a winter motorway journey can consume far more than the same route in June. Plan the winter journey, not the summer one.
Common mistakes
- Driving an EV on the motorway the way you drove a diesel — A diesel is at its best at 70 and barely notices the difference from 60. An EV notices a great deal, because there is nothing else consuming energy for the aerodynamic penalty to hide behind.
- Leaving roof bars on year-round — On an EV the drag penalty translates directly into lost range, and the effect is proportionally larger than the fuel penalty on a combustion car. Two minutes to remove them is worth real miles.
If it doesn't work
Range estimate drops far faster than the miles travelled
Cause: The estimate was based on recent gentler driving and is recalculating for motorway speed — Fix: Normal. The guess-o-meter is a rolling average of recent consumption, so it always lags a change of driving style. Use the percentage and your own consumption figure instead.
Nowhere near the official range figure
Cause: Official figures come from a standardised mixed cycle that is not a motorway run — Fix: Expect a substantially lower figure at sustained motorway speed, and lower again in winter. This is universal across manufacturers rather than a fault with your car.
Consumption much worse with a full car and luggage
Cause: Mass matters on gradients and in acceleration, though less than drag at a steady speed — Fix: Real but secondary. Roof-mounted loads cost far more than the same weight inside the car.
Motorway range worse than last year
Cause: Colder weather, different tyres, or gradual battery degradation — Fix: Compare like for like — same route, similar temperature. A few per cent of capacity loss over years is normal; a sudden change is worth investigating.
Arrived at a charger with much less than predicted
Cause: Headwind, gradient, or higher speed than the plan assumed — Fix: Build a margin in. Planning to arrive with fifteen to twenty per cent rather than five removes almost all of this anxiety.
Questions people ask
How much range does slowing down actually save?
It varies by car and conditions, but the relationship is steep — the power needed to overcome drag rises with the cube of speed, so the saving from a modest reduction at motorway speed is disproportionately large. The car's own consumption display shows your specific figure within a mile or two.
Does using the heater really cost that much?
In an electric car, yes, particularly in the first few minutes from cold. A heat pump, fitted to many newer EVs, reduces it substantially. Heated seats and a heated steering wheel deliver comfort for a fraction of the energy and are the standard winter strategy.
Why is my town range so much better?
Because an electric motor uses nothing when stopped, is efficient at low speed, and recovers energy every time you slow. All three of those advantages disappear at a constant 70 mph, leaving only aerodynamic drag, which is where a combustion car's relative weaknesses also disappear.