Terrain and Energy Use

Most drivers have an intuitive understanding of the way terrain affects their car. It’s similar to the way terrain affects people. Going uphill is harder and takes more energy. Going downhill is easier and sometimes you even get a little boost from gravity. What’s less clear is how significant this impact is on the range of an EV. How much of the battery is drained on an uphill slog? How much charge can you get back through regenerative braking? And why doesn’t Tesla account for terrain in their dashboard range estimate?

The Data

There aren’t many studies that look specifically at the effect of terrain on car mileage. We know road grade impacts fuel consumption in gas cars, leading on average to a 1% to 9% increase in fuel use. One study found that flat routes have 15% to 20% better fuel economy than hilly routes. No matter the incline, BEVs are more energy efficient than conventional vehicles. Fuel consumption (in gasoline gallon equivalents) for electric vehicles steadily increases as road grade increases, but for conventional vehicles, it increases drastically once they start going uphill.

A nice perk with EVs is that going downhill means using almost no energy - thanks to regenerative braking capabilities. Regenerative braking technology allows EVs to recapture kinetic energy when braking. Some Tesla drivers have reported recapturing 15% to 32% of their energy use with regenerative braking. But, know that the net energy usage over a roundtrip ride will still use up range: uphill driving uses more battery power than going downhill can restore , despite the boost to the vehicle’s range.

Car on mountain roads

The Trouble with Tesla’s Predictions

Tesla vehicles have some of the best reported ranges in the EV market. In fact, they’re a little too good to be true. Tesla was fined over $2 million by the South Korean government for exaggerating their driving ranges and is under investigation by the U.S. Department of Justice for inflated range estimates. Last year, a report from Reuters revealed the automaker used specially tailored algorithms to give “rosy” predictions of how far their vehicles could go on a full battery. Surprised by the stark difference between their car’s estimated range and its actual range, many Tesla drivers tried to make appointments with the company’s service centers, only to have their appointments canceled by a special “Diversion Team.” At the behest of its CEO, Elon Musk, Tesla worked hard to give potential buyers an optimistic view of what its cars were capable of. Edmunds tested eight Tesla models and not one of them was able to match its EPA range estimate in real-world testing. After considerable backlash, Tesla lowered its range estimates this year by about 6%, making them more realistic. 

Part of the problem with Tesla's range predictions is that the dashboard values don't factor in external factors such as terrain or temperature.

How to Understand Energy Usage

Tesla’s “Rated Range” on the dashboard doesn’t take into account external factors like temperature, driving efficiency, or terrain. In a Tesla, the trip prediction screen is the best range predictor because it accounts for road terrain using your destination. There are also other estimates: Recurrent created a Real-World Range feature for Tesla drivers to help them understand what’s really going on with their battery. Real-World Range is what typically happens in day-to-day driving based on over 360,000 discharge sessions, covering over 20M miles, across nearly 10,000 Teslas. Recurrent’s estimate is based on how real people actually drive, not controlled lab tests in ideal conditions and optimistic advertising spins. To get the most accurate range prediction available, sign up for our free platform.