2013 Tesla Model S: Regenerative Braking
August 20, 2013
Last week's two-night adventure in our long-term 2013 Tesla Model S proved fruitful in demonstrating one of the car's better features: adjustable regenerative braking and one way it could be improved.
I began experimenting with the two modes (Standard and Low) on my way home from work and it was immediately clear that the "Standard" setting is far more aggressive. Enough so, in fact, that I began to wonder if the brakes lights were triggered simply by lifting off the throttle. So, I did an experiment to find out.
At home I had my wife drive up and down our street in both modes. We designated two points on the street, one where she was to lift off the throttle and another where she began applying the brakes. In the "Standard" setting the brakes lights came on at the lift-throttle location. In the "Low" setting they came on further down the street at the braking point.
So in "Standard" mode the brake lights probably illuminate every time the driver lifts off the throttle.
Now this isn't a truly scientific test. It could be the case that the brake lights are triggered by a certain level of longitudinal g-load (deceleration) rather than simply by lifting off the throttle, and that the standard setting is more capable of generating that level of deceleration. Either way, though, the result is this: When you lift off the throttle in the "Standard" setting, you'll likely trigger the brake lights.
This is a blessing and a curse. Obviously, if you're slowing down rapidly enough, people behind should know. Tesla and I disagree about that rate.
Here's where the subtlety is lost in the Model S. Any conventional car that allows you to lock the relationship between the engine and drive wheels doesn't trigger the brake lights every time you close the throttle. In those cars you're able to achieve the same or greater deceleration without triggering the brake lights. The Tesla's setup bothers me because in Southern California every time you apply the brakes it affects hundreds, if not thousands, of others behind you.
I simply don't want to trigger the brakes lights every time I lift off the throttle. Let me be clear: I also don't want to be rear-ended. However, I've been using engine braking as a subtle means to slow a car, ease into gaps, and gracefully maneuver without brake lights as long as I've been driving. It's a polite way to do things. And in 24 years of driving this way I haven't been rear ended as a result.
Possibly, I'm the only one on Earth (or at least in Southern California) to whom this has occurred.
Here's my suggested solution for Tesla. Rather than using two modes, the regenerative braking adjustment should be on a rheostat. It could be adjusted using a slider on the touchscreen. Even if the range were calibrated using the existing two settings as extremes, the driver could more precisely control his or her desired decel rate. This would allow Tesla to decouple the brake light trigger from the throttle (assuming that's how it's currently set up).
Keep the brake lights on the brake pedal. Keep traffic moving. Let the driver choose. After all, it's his car.
Josh Jacquot, Senior Editor @ about 7,000 miles