What Determines the kWh/100 km Value? Tracing Efficiency Losses

The kWh/100 km figure shows the amount of energy drawn from the battery for the vehicle to travel 100 kilometers. This figure is determined by every loss point in the energy chain extending from the battery to the wheels - motor and inverter efficiency, heating and cooling load, aerodynamic drag and rolling resistance. Even the same vehicle, the same battery, and the same road can change this figure significantly under different conditions.

When you look at an electric vehicle's consumption table, you are actually reading the last line of an energy flow. Every kilowatt-hour leaving the battery makes a journey from the inverter to the motor, from the motor to the wheels; along the way it is consumed as heat, as magnetic losses, and as the resistance the tires press against the road surface. In this article, we will follow that journey from beginning to end and explain, through the chain of losses, why the same vehicle can show 14 one day and 22 kWh/100 km the next.

From Battery to Wheels: Where Does Energy Get Lost?

The electric drivetrain is structurally more efficient than the gasoline drivetrain; however, "efficient" does not mean "lossless". Every link in the chain has its share. The battery's internal resistance, the inverter's switching losses, the electrical and magnetic losses in the motor, and the mechanical friction in the drivetrain - all convert part of the energy drawn from the battery into heat.

The most loss-prone link in the chain is not the motor. Lithium-ion batteries exceed 99% coulombic efficiency, meaning the battery loses almost nothing as heat. The motor is different: ohmic (copper) losses in the windings, iron losses in the magnetic circuit, and the losses the magnets themselves are exposed to in permanent magnet motors limit the conversion of electrical energy into mechanical energy. The motor converts about 80% of electricity into mechanical energy; the theoretical maximum thermal efficiency of a gasoline engine with hundreds or even thousands of moving parts stays in the 35-40% band, and only 15-30% of the fuel energy reaches the wheels. This single comparison summarizes why the electric vehicle's consumption figure is generally low.

The inverter sitting between the motor and the battery converts direct current into three-phase alternating current suitable for the motor, and the losses are reflected directly in range. Switching losses mean that the semiconductors give off some energy as heat every time they switch on and off; the higher the inverter efficiency, the better the range and thermal performance. The same inverter is also critical in regenerative braking, because during energy recovery the energy flows in the reverse direction, from the motor to the battery, through the same power electronics.

How Does Motor Type Affect Efficiency?

There are two basic motor families in electric vehicles: permanent magnet synchronous motors and asynchronous (induction) motors. The origin of the difference lies in a physical principle called slip. In a synchronous motor, the rotor rotates in step with the stator's rotating magnetic field; in an asynchronous motor, the rotor deliberately lags behind the stator field in order to produce torque, and this difference appears as losses in the rotor circuits. For this reason, permanent magnet synchronous motors are generally a few points more efficient - it is stated that the difference is on the order of 2-3%.

On the other hand, the asynchronous motor has its own advantages: it is self-starting, delivers solid performance at high speeds, and carries no magnet cost. For this reason, many manufacturers prefer a hybrid setup: a synchronous motor for the main drive where efficiency is critical, and an asynchronous motor for the secondary axle. When reading consumption figures, knowing which motor type the vehicle carries explains part of the one-or-two kWh difference between two vehicles in the same class in the table.

Speed and Aerodynamics: The Factor That Raises Consumption Fastest

The main reason an electric vehicle consumes more energy on the highway than in the city is a simple rule of physics: aerodynamic drag increases with the square of speed. When you double your speed, air resistance quadruples; the power required to overcome it grows even faster. This is why electric vehicles become exponentially less efficient at high speeds, and the highway value in the range table is always above the city value.

The scale is concrete: aerodynamic drag can contribute up to 50% of total consumption at highway speeds. Reducing drag by 10% improves highway efficiency by about 5% - which explains why differences in front bumper or wheel cover design matter. An extension of this rule is this: the theoretical most efficient speed of an electric vehicle is very low. Because fixed consumers such as air conditioning, heating and electrical systems take a relatively large share at low speeds, while drag becomes dominant as speed increases. In practice, the most efficient band is the middle region where fixed consumers are worn down and drag has not yet exploded.

Tires, Wheels and Rolling Resistance

As speed decreases, air resistance fades and rolling resistance takes over the scene. Tires can affect an electric vehicle's range in the 20–40% range. In a gasoline car, roughly 5% of the energy is lost in the tires, while in an electric vehicle this figure rises to 16% - because the total energy in an EV is already small, so each loss's share is therefore larger.

Tire pressure is also part of the equation: every PSI below the recommended pressure increases rolling resistance and draws more energy from the battery. Wheel size, meanwhile, makes a difference that even shows up in manufacturer documentation. In the Hyundai Ioniq 6 carrying the same 77.4 kWh battery, switching from 18-inch to 20-inch wheels - that is, only an 11% increase in wheel size - brought a 14% drop in efficiency. Larger wheels mean a wider contact patch and stiffer sidewalls compared to thick-profile tires; the small wheel and thick profile combination still delivers the longest range.

• Maintain the recommended tire pressure; every missing PSI shows up on the battery bill.
• Snow, mud, and cold ground conditions increase rolling resistance.
• There is a direct trade-off between design and range in wheel selection.

Cabin Heating and Cooling: The Invisible Consumption

In a gasoline car, cabin heating comes almost free of charge from the engine's waste heat. An electric vehicle has no such luxury: the air conditioning, heating, and all auxiliary systems are fed directly from the high-voltage battery. In other words, a portion of the kWh/100 km value never reaches the wheels; it goes to the heater element and the compressor. An average vehicle needs 4–8 kW of heating power in cold weather - a figure close to a motor's propulsion power, and one that can easily double consumption at low city speeds.

The effect of cold is measurable in scale. At temperatures around freezing point, the average range loss is about 20% and increases as the air gets colder. In one study, at -7°C the range of a fully electric vehicle dropped by 41%; under similar conditions, the drop in a gasoline car was 10%. Cold-weather range loss is not caused by a single factor: cabin heating, the high internal resistance of a cold battery, and increased rolling resistance all contribute to the same bill. The heat pump is the main technology that eases this bill; compared to a resistive heater, it can increase range by 8–10% in cold conditions.

Extreme heat also increases consumption: in the 46–50°C range, energy consumption rises by up to 28% compared to 26–30°C. The compressor load and the thermal management system's effort to keep the battery cool are the main reasons for this. Within the optimal temperature band - roughly between 10 and 30°C - electric vehicles use their full range or even more; this band is the environment closest to the reference conditions under which official consumption figures are measured.

Why Does the City Beat the Highway? The Role of Regenerative Braking

In a gasoline car, a traffic light is pure waste; in an electric car, braking is an energy harvesting process. Regenerative braking converts the vehicle's kinetic energy into electricity by running the motor as a generator and writes it back to the battery. Up to 60-70% of the captured kinetic energy can return to the battery, and 25-40% of braking events can be recovered through regeneration. In mixed city/highway use, recovery is estimated at around 22% for fully electric vehicles. In stop-and-go traffic this figure becomes even more significant, and on downhill descents the battery genuinely gains energy back.

The result is the opposite of the classic habit: many models achieve 15-25% better energy economy in city driving, while efficiency drops by 10-30% on the highway. Much of the city-highway difference in the same vehicle's kWh/100 km figure comes from this - in the city, braking feeds energy back, while on the highway our only job is to overcome drag.

Difference Between Official and Real-World Figures

The kWh/100 km value in the catalog is produced under a defined test protocol, at a measured temperature, and with a specific wheel-tire combination. The real road tells a different story: driving speed, outside temperature, cabin heating, tire pressure, load, and driving style all write different figures for the same vehicle. Manufacturers openly state this too: range can vary significantly with temperature, terrain, battery age, and load. A deviation of up to 41% at -7°C shows the scale of this warning.

When reading consumption figures, it helps to keep this table in mind:

Practical Ways to Reduce the Figure

If you know the chain of losses, you also know where to start to improve the figure. Three items come to the fore: keeping speed in check, managing cabin load, and keeping tires under control. Reducing fixed consumption with a heat pump, lowering rolling resistance with the correct pressure and, if possible, smaller wheels, and limiting drag on the highway with speed discipline - together, these three produce a measurable difference in the same vehicle. It should also be factored in that 12-15% of the energy added to a battery is lost during the charging process; consumption occurs not only while driving, but also along the path from the plug to the battery.

In short, kWh/100 km is not a vehicle attribute but the result of a system. Battery, motor, inverter, tires, and air - all five leave their mark on that number. When you understand why the figure changes, estimating range is no longer a game of chance; it becomes a measurable engineering problem.

Sources

• Efficiency Matters: All About EV Efficiency
• Electric Vehicle Benefits and Considerations
• Use of energy for transportation: electric vehicles
• Impact of Cold Ambient Temperatures on BEV Performance
• Study: How Much Heat Pumps Boost EV Range
• How temperature and speed impact EV range
• How Temperature Affects Electric Vehicle Range
• EVs Explained: Charging Losses
• How tires impact your electric vehicle's range
• How to Optimise the Range of Your Electric Car
• Losses in Efficiency Maps of Electric Vehicles: An Overview
• A closer look at the losses in EV motors
• Inverters in Electric Vehicles: Function, Types, and Efficiency
• Extreme heat effects on electric vehicle energy consumption
• Regenerative braking system development
• Understanding regenerative braking in EVs