EV Off-Road Energy Consumption: What the Numbers Actually Say

The number that gets cited most often in discussions about EV range - whether in manufacturer spec sheets or range anxiety commentary - is the highway consumption figure. It’s the cleanest number to measure and the easiest to communicate. For the 97% of Australian EV drivers who spend their time on sealed roads, it’s the number that actually matters.

For anyone thinking seriously about off-road EV travel, it is nearly useless.

Off-road energy consumption in an EV is a different physical problem entirely, governed by different variables, and the gap between the highway figure and the off-road reality is large enough to completely reframe how you think about range planning.

Why the Highway Figure Is the Wrong Starting Point

On a sealed highway at 100–110 km/h, the dominant energy load in an EV is aerodynamic drag. Aerodynamic drag force scales with the square of velocity - double your speed and you quadruple the drag force. At highway speed, aerodynamic drag accounts for 60–70% of total energy consumption in a modern EV with good WLTP figures.

This is why EVs that look good on WLTP - measured on a combined city/highway cycle with significant low-speed urban driving - often disappoint on sustained highway runs. The Tesla Model 3 Long Range, rated at 19.7 kWh/100km WLTP, consumes around 24–26 kWh/100km at a steady 110 km/h. The Hyundai IONIQ 6, rated at 14.3 kWh/100km WLTP, consumes 17–19 kWh/100km at the same speed. Both are efficient cars - the deviation from the WLTP figure reflects the aerodynamic penalty of highway speed.

At 60 km/h on a smooth dirt road with no significant gradient, aerodynamic drag drops to a fraction of its highway value. The dominant energy losses become rolling resistance and drivetrain friction. And rolling resistance, it turns out, is highly sensitive to what you’re driving on.

Rolling Resistance: The Variable That Explains Everything

Rolling resistance is the force opposing motion as a tyre deforms and recovers on a surface. On smooth, hard asphalt, it is low. On soft sand, it can be three to five times higher. The physics are straightforward: in soft sand, the tyre sinks into the surface and has to continuously climb out of a small crater as it rotates. The energy cost is substantial and continuous.

The relationship between surface type and rolling resistance coefficient (Crr) is well documented in tyre engineering literature:

• Sealed road (asphalt): Crr 0.010–0.015
• Packed gravel/dirt road: Crr 0.020–0.030
• Soft sand (full flotation at aired-down pressure): Crr 0.060–0.100
• Dry, loose sand (partially sinking): Crr 0.100–0.160

The practical consequence is that driving on soft sand requires three to eight times more traction force than driving on asphalt, even at the same speed. Electric motors are highly efficient at converting electrical energy to mechanical torque - typically 90–95% - so the increased force demand translates almost directly into increased energy consumption.

A vehicle consuming 20 kWh/100km on sealed road at 100 km/h has roughly half that consumption attributable to aerodynamic drag and half to rolling resistance and drivetrain losses. Drop the speed to 60 km/h on soft sand and the aerodynamic component falls sharply, but the rolling resistance component at three to five times the hard-road value dominates. The result is a net consumption of 40–70 kWh/100km depending on sand conditions - not 20 kWh/100km.

What Rivian Owners Actually Record Off-Road

The Rivian R1T and R1S are the most extensively documented off-road EVs with real-world consumption data, primarily from North American desert and overlanding communities whose terrain closely resembles inland Australia. The numbers reported consistently in owner forums and journey posts, with commentary on what drives each figure:

• Highway (sealed, 100–110 km/h): 26–30 kWh/100km - aerodynamic drag dominant
• Graded dirt/gravel road (60–80 km/h): 28–35 kWh/100km - rolling resistance rises, drag falls
• Corrugated outback-style track (50–70 km/h): 35–45 kWh/100km - continuous vibration load and uneven terrain add consumption
• Soft sand (aired down, 30–50 km/h): 52–68 kWh/100km - rolling resistance multiplied three to five times over sealed road
• Technical rock/low-range terrain (10–25 km/h): 38–55 kWh/100km - lower than sand because very low speed kills aerodynamic drag; high continuous motor torque for wheel articulation is the remaining load

The rock crawling figure being lower per kilometre than the sand figure surprises most people. The explanation is that soft sand at 40–60 km/h combines elevated rolling resistance with enough speed to reintroduce aerodynamic losses. Rock crawling at walking pace eliminates speed-related loads almost entirely, leaving only the torque demand.

Australian 4WD owners in the early Rivian-adjacent EV community doing tracks comparable to the Canning Stock Route (mix of corrugations, soft sand, rocky sections) report planning figures of 50–60 kWh/100km as conservative estimates.

For a vehicle like the Rivian R1S with 135 kWh usable battery (the large pack variant), this implies a real off-road range of 225–270 km. For a 80 kWh vehicle - closer to what the Munro EV ships with - it implies roughly 130–160 km on mixed demanding terrain.

The Tyre Pressure Factor

Every serious 4WD driver knows you air down for sand. The flotation benefit - wider contact patch, reduced sinkage - is substantial and often makes the difference between getting bogged and not. For EV drivers, airing down is equally essential for traction management, but it carries an energy cost that ICE drivers often don’t need to worry about: increased rolling resistance.

At road pressure (35–38 PSI), a tyre has a relatively small contact patch and high Crr because it sits up on the sand rather than floating. At 16–20 PSI, the sidewall bulge creates a longer, wider contact patch that distributes weight more effectively - but this additional deflection and recovery work per rotation is the definition of rolling resistance.

The net effect is that aired-down tyres on sand have lower total resistance than hard-inflated tyres on sand (because you’re not sinking as deep), but significantly higher resistance than either on sealed road. The energy cost of properly-aired-down sand driving is irreducible. You need the flotation, and flotation costs energy.

Load, Gradient, and the Expedition Vehicle Problem

An expedition EV - loaded with 400–600 kg of gear, water, food, solar panels, and spare parts - is not the same vehicle as the empty press-launch version that produced the range figure on the spec sheet.

Added weight increases rolling resistance in rough terrain because heavier vehicles sink deeper into soft surfaces. It also increases climb energy demands on any significant gradient, though regenerative braking recovers some of this on descents. The combined effect of expedition loading on outback terrain is typically a 15–25% increase in consumption versus the unladen off-road figure.

On a vehicle consuming 55 kWh/100km unladen on comparable terrain, a 20% load penalty brings that to 66 kWh/100km. On 80 kWh of usable battery, that’s an effective range of 121 km per charge.

What This Means for Planning

The takeaway from this data is not that off-road EV travel is impractical. It’s that you need to plan around realistic off-road consumption figures rather than highway ones, because the gap is a factor of two to three, not a rounding error.

For any expedition involving significant soft sand, the 30 kWh/100km figure that sounds reasonable for rough dirt tracks is too optimistic. Plan for 50–65 kWh/100km on sandy terrain at aired-down pressures, and 35–45 kWh/100km on corrugated graded tracks.

The implication for solar charging is direct: more energy per kilometre means more solar generation needed per day for the same distance target. The mild-condition planning figures that make a 10 kW array seem sufficient on a moderate dirt road become inadequate on serious sand driving. For the Canning Stock Route specifically - which is predominantly sand and corrugations - daily consumption for a well-loaded expedition EV would likely be 50–60 kWh for 100 km of progress, requiring a larger solar array or a shorter daily distance target than the optimistic version of the plan.

None of the variables here are unique to EVs. A diesel 4WD burning 18–25 L/100km on sand instead of 10 L/100km on highway faces the same underlying physics. The difference is that diesel arrives in cans at a servo, and solar energy arrives whenever the sun is overhead. Managing that timing is the real challenge of an electric outback expedition, not the consumption figures themselves.