Geotab: Driving speed biggest factor in EV range drop in summer months

Driving speed and aerodynamics – rather than air-conditioning and warm weather – are found to have the biggest effect on EV range in summer, says a recent study from Geotab.

Its data used anonymised telematics from more than three million trips, and compared how temperature and speed affect energy use in light-duty EVs, including family saloon cars and cargo vans. At speeds of between 50 and 80mph in temperatures of above 30°C, aerodynamic drag had a far greater effect than range on cabin cooling.

The findings showed that even modest speed increases can lead to sharp reductions in EV range in summer. A 65kWh electric van cruising at 50mph in 30°C heat with the A/C on has a typical range of around 143 miles.

If speed is increased to 60mph in the same weather, then range drops to 121 miles. At 70mph, it falls to 103 miles, and at 80mph, range becomes 88 miles – this is a total range reduction of 39% over a period of just 30mph.

While all-electric saloon cars are more aerodynamically efficient than vans, driving quicker in the same conditions will still have an adverse effect on their range in summer.

At 50mph, some have a possible range of 277 miles with the A/C on, yet increasing to 60mph in the same environment will see range reduced to 251 miles. At 70mph, range is further slashed to 226 miles, while 80mph drops things further to 200 miles. Again, this is a 28% drop during the same 30mph bracket.

In short, the faster a car travels, the more it has to fight air resistance. In short, increasing speed by double requires four times the energy to overcome wind resistance. This is far more than an air-conditioning system will ever use.

The effect of warmer air temperature is more noticeable at lower speeds – the draw from the A/C is more noticeable as air resistance is otherwise minimal. Yet the faster a car travels, the less significant the air temperature becomes in relation to the energy required to maintain speed.

Charlotte Argue, the senior sustainability manager at Geotab explained: “Drivers tend to worry about using the aircon in hot weather, but our data shows that your right foot can make the biggest difference, particularly at high speeds. Just slowing down by 10 or 15 mph can extend your range by 20 to 30%, depending on the vehicle.

“Modern EVs have increasingly large batteries, and many can comfortably handle most daily driving – including fleet routes – on a single charge,” she added. “But range, on EVs or ICE vehicles, will always vary with real-world conditions: temperature, topography, traffic, and yes, speed.”