Regenerative Braking: BMW i3 Versus Tesla Model S 70D

JUL 24 2015 BY STAFF 22

Over on BMWBLOG, you’ll find a highly detailed article on regenerative braking. The article explains this feature in depth and then discusses how various electric cars implement regenerative braking and one pedal driving. It’s a thought-provking read, so do check it out here, but be warned, it’s long.

Here’s a snippet from the article:

Four-wheel versus two-wheel magnetic braking

Magnetic braking only works through the wheels connected to the motor. The i3 is rear-wheel drive, and therefore the magnetic braking is through the rear wheels only. Since the front wheels are the most effective at braking (due to weight shift on deceleration), the effectiveness of the i3’s magnetic braking could be better. The MINI E, with its front wheel drive, could support stronger magnetic braking, and did (but the RWD ActiveE also had magnetic braking levels higher than the i3). Both trial cars experienced some magnetic braking anomalies in certain conditions, however.

The all-wheel drive Tesla Model S 70D provides balanced magnetic braking (and more even tire wear). As implemented, its magnetic brakes are independently controlled front and rear; resistance is automatically adjusted at each axle to match conditions. It should be less prone than the i3 to traction loss during difficult braking conditions.
The 70D therefore has the potential to have stronger magnetic braking than either the i3 or the MINI E. But does it?

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22 Comments on "Regenerative Braking: BMW i3 Versus Tesla Model S 70D"

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skryll

So what’s the short answer to ‘but does it?’

miggy

The Outlander PHEV has the best regenerative braking system out there.

The article doesn’t really say for sure, but Tesla says the the P70D has the same amount of regen as the single motor ones, and still requires the brake pedal to come to a complete stop. So, small BMW win, but the Tesla gets points for even braking and tire wear, plus the ability to upgrade software for braking improvements in the future.

Foo

Perhaps the testers failed to turn off Creep Mode and so concluded that the brake pedal is required to stop?

Rob Andrews

Not yet, may come some day in a software update

pjwood1

The Model S takes getting used to, versus the Volt. It’s more aggressive regen, or triggered over less pedal travel. The i3’s regen happens over about the same travel, but in an EV with about half the weight. It feels almost too strong, IMO.

Liz

During my test drive of an i3, regen felt really strong and surprised me every time it engaged. When I bought the car and drove it home, I was used to it by the time I got to my driveway.

Brent

I own both an 85D (my wife’s car) and an i3 BEV. While I prefer the tesla for most things, I wish it had the more aggressive regen of the i3

wraithnot

We’re in a similar situation with an i3 BEV and a Model S (although S85 instead of 85D) and I completely agree both with preferring the Tesla for most things, but preferring the regen in the i3. I also think BMW did a better job with things like the interior storage compartments, more comfortable seats, oh sh*t handles over the doors, and coat hangers. But BMW really dropped the ball when it comes to the smartphone app, the display in front of the driver, and how remaining range is reported. The limited range is also more of an issue than we originally thought since my wife realized an alternate route to her work with more freeway driving worked better at certain times of the day.

Sounds like BMW got more of the “car stuff” right and Tesla got more of the “software stuff” right. That sort makes sense with the engineering backgrounds of each company.

Pushmi-Pullyu

Brent said:

“I own both an 85D (my wife’s car) and an i3 BEV. While I prefer the tesla for most things, I wish it had the more aggressive regen of the i3”

Doesn’t the Model S have a selectable setting for how aggressive the regen is?

Yes.

Bill Howland

I too prefer the I3’s regen.. I seem to remember it is even more than the Roadster’s I used to own.

The model S’s regen seemed similar to the chevy Volt in both modes (almost non-existent in D, and reasonable in L)

The ELR’s regen on demand is pretty good, but not as good as the old Roadster or I3.

Does this mean a LEAF with front-wheel regen braking, is (potentially) better than i3?

Three Electrics

Potentially, yes. Actually, not even close.

Erhard

The magnetic braking depends on the velocity and physics tells us that it can not bti g us to a complete stop.so mechanical braking is always needed at lose velocities.my fiat 500e transitions at around 8mph to mechanical and unfortunately it is hard to miss, meaning poor transition implantation

wraithnot

I think the i3 also transitions to mechanical brakes at really low speeds. But it’s implemented so well that I didn’t notice it until one day after a rain storm when the brake rotors were rusty and the friction breaks made a grinding noise until the rust wore off.

Loboc

When using ACC (Adaptive Cruise Control), ELR comes to a complete stop automatically if the car in front stops. It seems to engage the parking brake to hold at stop since it takes a little more push on the accelerator to get it rolling again.

Seems to me that one-pedal drive software could use the same logic so that you don’t have to manually hit the friction brake pedal for non-emergency stops.

Phr3d

good stuff Wraithnot and Loboc, Thanks!

Craig Capurso

I want as much regenerative as possible but I want control of it, the most efficient driving is to coast as much as possible I have done that for years with diesel powered truck if I see a red light I get off the gas and try to cost, when it turn green I get going again seems simple to me. Most people drive it seems to me with what I call a toggle switch foot to the floor till the get to with an a foot of stop light than full brakes to stop. These are the people that will po po electric cars. My wife is one of them I can hardly stand to be in the car with her?

Josephus

I was hoping the article might shine some light on a question I’ve had for a while, but alas.

Which is more effecient when coming to a stop:
1) softer regen over a longer distance?
2) stronger regen at the end?

I realize that the motor might generate the same amount of electricity in both senarios, but how fast can the batteries absorb it? If it’s more gradual do they get more of it? I wish I had gauge to say how many watt hours were generated in each instance.

Tangent:
I have a Ford Focus Electric, and I absolutely love the stick shift’s ability to set more aggressive breaking. Super fun factor.

Until….

I test drove and i3 and Tesla P85D and realized just how weak my “strong” L position regen was. Now I’m soured on the stick shift regen and find myself yearning for one-pedal driving with super aggressive regen.

Maybe if they combine both stick shift selectable maximum regen and stronger regen….?

The most efficient is zero regen and no brakes. If you need either, except for a downhill stop, then you didn’t begin to slow / stop soon enough.