Speed is the biggest range factor you control in an electric car. Air resistance rises with the square of speed, so the energy spent pushing air per kilometre climbs steeply as you go faster, and at highway speeds that’s where most of the battery goes. That’s why an EV’s highway range is usually well below its rated range, and why easing off from 120 to 100 km/h, or from 75 to 65 mph, can rescue a tight leg to the next charger. Cold weather is the other big factor, mainly because of cabin heating.
Why does speed cut EV range so much? #
An EV’s energy use per kilometre comes from three main places:
- Rolling resistance from the tires. Roughly constant per kilometre, whatever your speed.
- Aerodynamic drag. The force grows with the square of your speed through the air, so the energy per kilometre does too.
- Accessories: heating, air conditioning, lights, electronics. These use energy per minute, not per kilometre.
At city speeds, drag is small and EVs are very efficient, especially since they don’t waste energy idling in traffic and recover some energy when braking. At highway speeds drag takes over.
Here’s how the aerodynamic part alone changes with speed:
| Speed change | Aerodynamic energy per km or mile |
|---|---|
| 100 → 110 km/h | +21% |
| 100 → 120 km/h | +44% |
| 100 → 130 km/h | +69% |
| 60 → 70 mph | +36% |
| 65 → 75 mph | +33% |
| 65 → 80 mph | +51% |
Your total consumption rises by less than that, because rolling resistance and accessories don’t scale the same way. But at motorway speeds drag is the largest single load, so these differences show up clearly on the car’s energy display.
Wind counts too #
Drag depends on your speed through the air, not over the ground. A GPS speedometer measures ground speed. Driving at 100 km/h into a 20 km/h headwind, your car pushes air as if it were doing 120 km/h, with the extra energy that brings. A strong headwind can cost as much range as driving 20 km/h faster; a tailwind helps.
How much does cold weather cut EV range? #
A lot, mostly because of heating. According to the US government’s fueleconomy.gov, at 20°F (−7°C) with the cabin heater on, EV fuel economy can drop about 39% in mixed city and highway driving and range can drop about 41%, compared with 75°F (24°C). About two-thirds of the extra energy goes on heating the cabin. Without the cabin heater, fuel economy is about 8% lower and range about 12% lower at 20°F.
The same source suggests two fixes: preheat the cabin while the car is still plugged in, and use seat heaters instead of heating all the air in the cabin.
How to measure your real EV range with a trip meter #
The car’s range estimate is based on recent driving, so it can be optimistic after a gentle week and gloomy after a fast one. Measuring your own consumption tells you what your car does on your roads.
- Start a trip at a known state of charge. Reset the car’s trip meter, or press Start in a GPS trip meter, and note the battery percentage.
- Drive a typical leg. A steady highway run, a commute, whatever you want to measure.
- Note the distance and the percentage used.
- Work out distance per percent: distance ÷ percentage used.
- Project your range: multiply by the percentage you’re willing to use.
Example: you drive 42 km and use 15% of the battery. That’s 2.8 km per percent. From 90% down to a 10% buffer is 80%, so your realistic range at that speed and temperature is about 224 km.
Repeat at different speeds and in different weather, and you’ll have a small table of your own real-world range that beats any estimate.
Where a GPS speedometer helps #
Speedometer GPS doesn’t read your car’s battery or calculate efficiency, so the percentage comes from the car’s own display. What it adds is a clean record of how you drove each leg. A saved trip keeps the distance, average moving speed, top speed, time and a speed chart. Compare two runs of the same route and you can see how much the faster one cost.
Its speed limit alarm is useful on a long EV trip too. Set it to the cruising speed you’ve chosen for range, say 100 km/h or 65 mph, before you leave, and it buzzes and beeps if your speed creeps above it, with no need to watch the number. We compare that manual approach with map-based alerts in speed limit alert apps. At night, HUD mode puts the speed in the windshield.
GPS distance doesn’t depend on your tire size, but it loses distance in long tunnels; see trip odometer vs GPS distance.
Ways to reduce range anxiety on a road trip #
- Plan each leg with a buffer. Aim to arrive with 10% to 20% left, more in winter or at night.
- Know your backup charger on each leg before you need it.
- Slow down on the tight legs. Easing off 10 to 20 km/h on the stretch before a charger is the quickest range you can buy.
- Watch the wind and temperature forecast, and allow for strong headwinds and cold.
- Precondition the battery and cabin while plugged in, if your car supports it.
- Remember hills even out. Climbing costs range, and descents give some back through regenerative braking, but not all of it.
Your car’s speedometer probably reads a little high compared with GPS, so if you set a range-saving speed on the dashboard, you may be going slightly slower than you think. See why your car speedometer reads high.
Frequently asked questions #
What speed gives the best EV range? #
There’s no single number, because it depends on the car’s shape, tires and the weather. In general, lower steady speeds use less energy per kilometre, since drag grows with the square of speed. On a highway, the best practical speed is the lowest you’re comfortable with in the flow of traffic.
Does cold weather really cut EV range that much? #
It can. Fueleconomy.gov reports range can drop about 41% at 20°F with the cabin heater on in mixed driving, but only about 12% if you don’t use the heater. Preheating while plugged in and using seat heaters helps a lot.
Does a headwind affect EV range? #
Yes. Drag depends on your speed through the air, so a headwind acts like driving faster. Driving at 100 km/h into a 20 km/h headwind costs roughly as much energy against drag as 120 km/h in still air.
How accurate is my EV’s range estimate? #
It’s usually based on your recent driving and current conditions, so it can be off when those change, for example when you switch from town driving to a fast highway run. Measuring your own distance per percent of battery gives a more reliable figure for a particular kind of trip.
Can a GPS speedometer app show EV efficiency? #
Speedometer GPS doesn’t read the car’s battery, so it can’t show efficiency directly. It records distance, speed and time accurately, and you combine that with the battery percentage from the car to work out your real range.