# More efficient stopping mode roll or hold?

I am trying to figure out which stopping mode, roll or hold, is the most efficient as far as putting more energy back into the battery? I use regen all the time. Love the one-pedal driving. I just want to drive it as efficiently as possible. Thanks

• I am only guessing but I would think "Hold" would be more efficient than using energy to moving the car along
• So: I happen to own a Prius; the M3 I drive (fairly often) is the SO's car.
On Priuses, regen only occurs when (a) one is off the gas and slowing down, say, from 65 down to 50; or (b) one touches the brakes _lightly_. If one touches the brakes lightly, it's regen that brakes the car. Touch the brakes heavily, or at under 5-10 mph, and it's brakes all the way.
So, Prius people interested in maximizing mileage attempt to stick with regen as much as possible.. And, more to the point, for the high-mileage fanatics, never to use regen, or brakes, at all.
Why not use regen at all? Because regenning means energy from the wheels goes into the motors (so far, so good: That's mechanical, not much energy loss), through a bunch of switching transistors (not so good - they're efficient, but it sure isn't 100%, more like 80%-95%, depending upon speed and such), through a voltage doubler circuit in the reverse direction (Priuses are a little weird), which has more losses, and then into the battery.. which, while it's fine converting electrical energy to chemical, that's not 100% efficient either.
Then, when one attempts to use that energy, one has to come out of the battery (losses), through the voltage doubler (more losses), through the switching transistors (lots more losses), I^2-R losses in the wires (losses), and finally motive force.
Them's who did the math over there claimed that, given the round-trip nature, 50% of the energy from braking was lost in the round trip.
Now, if one is slowing down with Just the Brakes, all of that kinetic energy gets turned into heat, period. So, recovering 50% of the kinetic energy of the car when slowing is sure better than losing 100%, hence, Priuses' 50 mpg in-city rating. (At least, that's part of the reason).
So, the high-milers with Priuses can get close to 100 mpg (or so I've heard, never tried it myself) by getting the car up to, say, 65; then _very_ _slowly_ slowing down to, say, 55, lather, rinse, repeat. There's this standard gauge on a Prius that allows one to gauge the amount, or lack thereof of regen, and this gets used in spades for something like this. And this is provably better than running at a steady rate of speed. At least, on a hybrid Prius. Most of the time in this scenario one isn't using gas at all, hence the near-100 mpg numbers. And they're keeping the kinetic energy out of the battery, too, hence the very-slow slowdown.
Out of curiosity I asked around here when I showed up in 2018 if there were any known tricks like that for a Tesla. The answers were, variously, "Huh?" and "No".
Now, at least I'd argue that Teslas on regen have the same issue with losses that the Priuses of the world do what with the round trip to & fro from the battery losing energy. Yep, regen is still better than using the brakes, sure. And it doesn't answer questions about getting up to speed, either. But nice and slow on the deceleration is better for overall efficiency than braking hard with regen.
Which, basically, means that the old adage of "Avoid jackrabbit starts and stops" still holds for electric cars. Any surprise on that? :smile:
• Extremely little difference in roll and hold. It’s really a matter of preference if you want the car to press the frictions brakes for you or not
• Don’t think it makes any difference. The Hold setting just determines what happens after the car has already come to a complete stop.
• If you can coast, it’s better than braking as it takes less force to get back to road speed. That being said, the difference between slightly rolling and completely stopping is going to be in the noise.
• Since you would have to apply brakes at some point (at least driving safety and halfway normally) that energy would be lost while letting the regen stop the car for the final inch converts it to stored energy in the battery.
• Inconsequential.
• > @Bighorn said:
> Inconsequential.

Diminishing returns are a bitch
• I would hypothesize that use of hold mode might cause the driver to become a bit less efficient. Hold mode sort of disconnects the driver from the processes of regen and friction braking. When in independent control of each, one can more easily anticipate one's braking, maximizing the regenerative portion and minimizing the friction part. Regen braking is more efficient than friction braking.
It would theoretically be possible to do it just as well with hold mode, just a bit harder.
I doubt the the difference would be significant though.
Personally, I don't think it really matters since Teslas are so efficient anyway unless one is just playing around trying to optimize to the max extent possible.
• One of my cars has hold mode and the other does not. The only difference hold mode makes for me is whether I keep my foot on the brake when stopped. Seeing as no regenerative energy is derived from a motionless car, there is no difference whatsoever.
• > @Bighorn said: Seeing as no regenerative energy is derived from a motionless car, there is no difference whatsoever."

Musk pretty much debunked that theory when he noted the more aggressive regen would add range by capturing more energy.
• ^ only for people who can’t grasp basic physics
• > @M-A-B-MCMLXXX said: > ^ only for people who can’t grasp basic physics"

Not that @Bighorn doesn't grasp basic physics just that the builder of the car contradicts his theory on regen.
• I would wager Elon Musk has built fewer cars than I have, and that fishev understanding his thoughts is like an ant understanding relativity.
• Can’t fix stupid.
• An owner would understand what brake hold is and know that it has nothing to do with regen. It’s the actuation of an electric brake. When the car stops. You hear it engage. Not related to regen because regen does not happen at speeds approaching zero. High school physics.
• > @Bighorn said:> An owner would understand what brake hold is and know that it has nothing to do with regen. “

You don’t understand the original question. Should he let it roll or use regen and brake hold.

Musk says to use regen. You say let it roll.

Who to believe.
• False
• > @lems82670_98343388 said:
> I am trying to figure out which stopping mode, roll or hold, is the most efficient as far as putting more energy back into the battery? I use regen all the time. Love the one-pedal driving. I just want to drive it as efficiently as possible. Thanks

To be clear, regen is less efficient than rolling and coasting to a stop. There is always energy loss with regen.

However, it is impossible to coast to every stop since you would gradually go from 50mph to 0mph and it would take 1 minute on extra long distance.

So it is more efficient to coast but more practical to regen.

At high speeds the energy you get back from regen is far greater from 50 mph to 40 mph as the kinetic energy stored is speed squared. So regen or roll from 10 mph to 0 mph has less significance than the high speeds.

However, if you want to set an hypermiling world record and go through 800 miles with your Model 3 on one charge you would need to never regen, always maintain around 30 mph and always coast to a stop, or never stop at all.
• > @FISHEV said:
> > @Bighorn said:> An owner would understand what brake hold is and know that it has nothing to do with regen. “
>
> You don’t understand the original question. Should he let it roll or use regen and brake hold.

He understand it perfectly well. The original question is about the stopping modes ROLL and HOLD, which can be configured in the car's menu.

Both of those modes use regen for slowing the car when you lift the accelerator pedal. The only difference is what happens at the very end, when the car is approaching a full stop (and not much kinetic energy is left in the car anyway, since kinetic energy increases with velocity to the second power).

> Musk says to use regen.

Both Musk and Bighorn do.

>You say let it roll.

No. He says use the ROLL mode. Which uses regen.

> Who to believe.

Both of them. They are both right.
• "To be clear, regen is less efficient than rolling and coasting to a stop. There is always energy loss with regen."

Except that's not really practical and you do have to use the brakes which means you lose the energy you could have recaptured.

As Musk noted, the hard regen will add range on the Tesla in normal driving.
• Let’s let the OP clarify,but this is not a regen question. He already maximizes regen. It’s about what mode exists to address the stagnant state. Maxxer is correct on the physics of coasting, but it’s not the question posed. If I’m misunderstanding it, I’m happy to elaborate.
• The OP question isn’t the best wording but it certainly reads to me asking about ROLL and HOLD mode. These have nothing to do with regen.
• > @zerogravitydrgn said: > The OP question isn’t the best wording but it certainly reads to me asking about ROLL and HOLD mode. These have nothing to do with regen."

If you are talking efficiency then yes it does involve the regen vs. rolling with no regen.
• I know it’s a tired trope, but “Idiot!”