Why Do Electric Cars Brake So Often?

The other day my wife was behind a Tesla and commented they used their brakes a lot more than other drivers.  Last summer I’d thought somewhat the same thing when driving behind a BMW i3. Was this our imagination or is there something to this?

Image of Tesla vehicle with bike on roof rack

Tesla electric vehicle with bicycle (Photo: Tesla Motors)

Regenerative braking

The answer, I found, lay in the regenerative braking system in both of these cars. For the most part, an electric motor and a generator are the same. If you apply electricity to a motor, it will turn. Likewise, if you turn a motor, it will generate electricity. Electric cars take advantage of this duality with a regenerative braking system. When the driver lifts a foot off the accelerator or go pedal (since it is not, after all, a gas pedal in an electric car) the motor works in reverse; instead of using electricity from the batteries to turn the wheels, the kinetic energy from the car’s movement is used to generate electricity that recharges the batteries.

Some electric cars (EVs) such as Tesla and BMW allow full regeneration. When a driver lifts their foot from the go pedal, the regenerative system causes the car to decelerate quite quickly, similar to pressing the brake pedal. People who own these will often talk about one pedal driving as they rarely need to use their brakes. Each time they lift their foot from the go pedal they’ll likely also activate their brake lights. They’re not really braking. But they are. Sort of.

Other EVs limit regenerative braking so their cars will respond more like a familiar internal combustion engine (ICE) with an automatic transmission. Rather than significant slowing, they coast a bit more and brake lights are not as necessary.

There are improvements coming to both. As drivers become more accustomed to electric, all EVs will likely allow full regeneration. As well, Tesla and BMW have both been faulted for brake light activation being too sensitive and are expected to make some adjustments.

KERS in Formula One

Spark-Renault all electric Formula E race car. (Photo: SBNation.com)

Spark-Renault all-electric Formula E race car. (Photo: SBNation.com)

Formula One vehicles have utilized this technology since 2009. Though not really an electric car they are a hybrid with a KERS or Kinetic Energy Recovery System. The driver can utilize the KERS motor as a brake that charges a capacitor or battery (typically about 60kW). When they need a bit of extra power, they can engage the KERS motor for an additional 80 or so horsepower.

Likewise, the new all-electric Formula E cars make significant use of regenerative braking and allow drivers fairly detailed control over how much regeneration is used through dials on the steering wheel.

New World

Electric cars are far from any kind of panacea. While they may reduce fossil fuel consumption as well air, water, and surface pollution (and noise pollution at lower speeds), they still require a lot of space to drive and park. Like all motor vehicles, they can be a dangerous weapon in the hands of the driver.

I do believe EVs are a significant improvement over ICE vehicles however, and we’re certain to see increasing numbers of them on the road. Currently, we’re adding about 60 per month to the Twin Cities roadways (primarily Nissan Leaf, Tesla Model S, and BMW i3, with a few Fiat 500e’s, and Smart ED’s) and that’s expected to continue to increase. Altruistic virtues aside, they can also work from an economic standpoint. For many people the savings in fuel and maintenance more than make up for the higher initial cost.

This is a bit outside normal streets.mn discussion but is presented in an effort to keep streets.mn readers the best informed on Planet Earth. Well, at least the best informed in the Twin Cities.

Walker Angell

About Walker Angell

Walker Angell is a writer who focuses mostly on social and cultural comparisons of the U.S. and Europe. He occasionally blogs at localmile.org, a blog focused on everyday bicycling and local infrastructure for people who don’t have a chamois in their shorts. And on twitter @LocalMileMN