Is coasting retarded like it is on the Roadster?

Is coasting retarded like it is on the Roadster?

I understand that on the Roadster, regenerative braking becomes active when the accelerator pedal is not pressed enough to maintain speed and that as a consequence, coasting functionality is retarded. I also understand that unlike the Toyota Prius, the regenerative braking in the Roadster is not in any way linked to the brake pedal.

Telsa has some very promising technology, but these are issues that impair the driving experience enough that every time I think about possibly getting one, I tell myself that it is not worth it because I cannot coast without having the regenerative braking activate.

Does anyone know if these issues have been fixed in the Model S or does Tesla Motor still consider them to be features? If they do consider them to be features, is it possible to turn them off?

SteveU | 14. Januar 2011

I've got a Roadster and in my opinion the way regenerative braking works in the Roadster is vastly better than in the Prius. The control of your speed is far finer and faster than with the Prius. If the model S were to work the way the Prius does, it would be a substantially less attractive car to me than if it works the way the Roadster does. Obviously different people can have different opinions and not everyone must like the way the Roadster works, but do not assert that it is a defect that needs to be fixed.
If you haven't driven a Roadster, I recommend you try it.

Douglas3 | 14. Januar 2011

Are you kidding, have you actually driven a Roadster? The accel/regen pedal is wonderful to use. One foot driving most of the time - you hardly touch the brake pedal. When I switch back to an ICE car I really miss it.

michiganmodels | 15. Januar 2011

I agree with SteveU and Douglas3. I test drove a Roadster and found the regenerative braking one of its top features. I'd go so far as saying, I would cancel BOTH my Model S reservations if the regenerative breaking feature is discontinued from the Roadster to the Model S.

Vawlkus | 17. Januar 2011

Look at it this way: there is no clutch or transmission in an electric car, so how do you think such a car could even be ABLE to coast?

Volker.Berlin | 17. Januar 2011

Vawlkus, I do not think there is a technical reason why an EV should not be able to coast. Even an electric motor could be free wheeling. It is a matter of intentional user experience design. I am not saying it is particularly good or bad the way it is in the Roadster, just that there is a reason for the way it is that is unrelated to technical constraints. And it is certainly important to get the details right. Just how much is the car slowed down by lifting the pedal to a certain degree -- as much as the designers must tweak this behavior, as much it is impossible to tell if it "feels right" without actually trying it in a real life car.

PatriciaS | 17. Januar 2011

Something that nags at me about the regen (non-accelerating) mode that makes braking unnecessary until you need to bring the car to a complete stop, like at a stop sign is that until one actually has to step on the brake, there is no indication to the cars behind you that you are slowing to a stop, like there is with an ICE vehicle. Maybe it would be a good idea to have a way to illuminate the brake lights when in regen in a phased manner, make them light up brighter when the vehicle slows to a stop, and then steadily brightly lit when stopped. It bothers me to not be able to warn those vehicles behind me that I intend to stop, and I think I'd really be upset if somebody rear-ended me because they didn't see my brake lights.

Roblab | 17. Januar 2011

Interesting, PatriciaS!
I live on a 1700' hill. It is 5 miles to the valley. I drive an ICE vehicle. And when driving downhill, I NEVER put on the brakes. I use lower gears to decelerate for hills and curves.
I have never had anyone get excited about not seeing brake lights burning on my car. We as humans have a neat thingy called a brain, and the brain is able to detect objects moving nearer or further away. If anyone rear ends me because they didn't see my brakes, California law holds them liable, not me. If I am stopped at a light, and getting ready to go when it turns green, my brakes are not on. If I am maintaining my speed, or decelerating, my brakes are not on.
By the way, Tesla has arranged that the brake lights go on with deceleration with regen. So you're covered. I'm not worried about the lights, but I am with dragging my brakes off, as many of our out of towners smoke the brakes halfway down hill.

ckessel | 17. Januar 2011

Roblab was a bit snarky about it, but he's right. Many sports car ICE drivers use engine braking pretty heavily, which has no brake lights, so a car slowing down without brake lights is nothing new. Tesla, as he noted, even causes the brakes lights to come on if the regen slows you down enough.

Discoducky | 17. Januar 2011

Cool safety feature = Brake lights coming on due to heavy re-gen effect.

Less chance of getting hit from behind.

bgoodwin | 17. Januar 2011

The brake lights on the Roadster DO come on during regen braking except in areas where it's illegal (I forget where that is, offhand).
I find the regenerative braking (without touching the brake pedal) one of the primary reasons I absolutely enjoy driving the Roadster.

Discoducky | 17. Januar 2011

@bgoodwin, wow, it's amazing to think that there's a law on the books somewhere that prohibits brake lights coming on for re-gen effect.

Wonder that the reasoning is?

It's pretty easy to go from 50 to 30 in quickly with a downshift (re-gen aside), which is a receipe for a rear ending.

IMHO, any heavy deceleration should come with an indication of some kind. Brake lights seem the obvious choice.

Dragon | 18. Januar 2011

The law is not somewhere. It's all over Europe. European Roadsters don't have the brake lights coming on by regen. Many people told me it's not a great problem, but I already fear one of the "I have to drive as close as possible"-jerks hitting me.

Timo | 18. Januar 2011

Really? Where in Europe? European cars require separate turn indicator (yellow) which is not in same circuit with brake lights, but not turning brake lights on with regen was news to me.

BYT | 18. Januar 2011

For those who have driven a Roadster, how does it handle going downhill if you take your feet off of the accelerator say while on the highway on a steep downgrade?

Vawlkus | 18. Januar 2011

I too, use gearing down to slow my car. If you think of doing that as being a mild form of regenerative braking (which it is, just without the power going to the battery in an ICE), then you should get the idea

Michael37 | 18. Januar 2011

I haven't driven a Roadster (really must arrange to do so...), but I have driven an EV-1 for 2.5 years and a RAV4-EV for over 7 years. Both cars were capable of coasting, and IMO it's an important way to drive efficiently.

I think it's fine to be able to control both regen and acceleration with one pedal (EV-1 could do this as well and I used to use it), but I'd like the option to simply coast as well, perhaps via a button on the shift lever.

ckessel | 18. Januar 2011

Why do you think coasting is an important way to drive efficiently? Based on what assumption?

Douglas3 | 18. Januar 2011

BYT if you take your foot off the accelerator on a downhill, it slows down. Regen is a lot like downshifting a manual transmission into 1st gear - it's quite strong.

Mark Petersen | 19. Januar 2011

well coasting is just a matter of finding the sweet spot between accelerating and regen
so Tesla only have to add maybe 5% of the speeder movement to coasting

0-5% strong regen
5-10 medium regen
10-15% light regen
15-20% coasting
20-40 light accelerating
40-60 medium accelerating
60-80 strong accelerating
80-100% insane accelerating

cablechewer | 19. Januar 2011

In my current ICE I do a lot of coasting. If I see traffic ahead is slowing I'll hit the clutch and coast for a bit to see if it speeds up or I need to brake. If I see the traffic light ahead has turned I will coast until I need to brake or the light will turn green and I won't have as much acceleration to do to get back up to speed.

Somewhere there is likely a balance between coasting and regen vs the energy required to resume travel at the speed you were using before you had to slow down.

Driving style, patience and the ability to anticipate what is happening around you will all factor into which you can extract the most distance from.

Vawlkus | 20. Januar 2011

IMHO that's a bad idea. When faced with a similar situation I'll take my foot off the gas, but I'm keeping the car in gear incase the moron behind me isn't paying attention and I need to avoid him.

Douglas3 | 20. Januar 2011

cablechewer, if I'm driving my Roadster and traffic slows ahead, I lift up the accelerator a little. Depending on where I set my foot, I can essentially coast, slow down a little, or speed up a little. You really have quite precise and instantaneous power control.

Also I feel there's an extra margin of safety if you have to go for the brakes. As soon as you lift your foot the car is decelerating and the brake lights are on - even before you get your foot on the brake! That's gotta be a good fraction of a second faster than in any other car, and it gives you that little bit of additional safety margin in a panic stop.

Also I completely agree with Vawlkus. Way back in driver's ed they taught us not to do that as you sometimes need to apply power to avoid an accident, and engaging the clutch takes extra time.

PatriciaS | 20. Januar 2011

I, too, drive mountainous terrain in an ICE, using the tiptronic option on my tranny, downshifting rather than riding the brakes, but I live in an area where there are a lot of twits that tailgate, so I resort to tapping the brake to get them out of my tailpipe. I think there will be a short learning curve to learn to drive an electric, non-coasting, regen-braking vehicle, but I certainly look forward to doing so!
Douglas, I'm happy to hear that you get brake lights when you are off the accelerator. I know it's the tailgater's fault if he hits you, but who needs the aggravation?
Basically, driving defensively and with anticipation, not making any sudden moves, is the best policy. Too bad not all drivers actually do it.

Volker.Berlin | 05. Oktober 2011

Interesting detail in this article:

By luck, one of the first I introduce myself to is Drew Baglino, who happens to be directly involved in setting up the Model S regen braking system. [...] When I pleaded for driver-adjustable regen on the Model S, he said this was under consideration. (Two days after the event, while writing up this report, on a whim I e-mailed Tesla boss Elon Musk and repeated my plea for driver-adjustable regen. Three hours later, I got this reply: "I totally agree that regen should be driver-adjustable and it will be on Model S." The message was Cced to JB Straubel, Tesla CTO.)

Volker.Berlin | 23. November 2011

Regarding coasting vs. regen, when I read about the BMW i3 I came across an interesting idea. Tesla, are you listening?

Personally, I think I would like strong max regen as a means to do "single foot driving" -- regen should be smoothly adjusted according to the position of the pedal, and should be strongest when the foot is almost lifted from the pedal. So far, so obvious, and my test drive in the Roadster convinced me that Tesla has a very good idea how to implement this and make it feel very natural.

Now for coasting. With the implementation outlined above, as it can be found in the Roadster, there is a very fine line where the car coasts or sails with neither propulsion not regen being active. It is almost impossible to hit that point with the pedal, and keep it there. Therefore, BMW seems to suggest for the i3, that the drivetrain is disconnected from the wheels and the car supports perfect coasting when the foot is actually lifted from the pedal. Put the foot on the pedal -- ever so slightly -- and regen kicks in, lift it off the pedal, and the car coasts.

Of course, electronics need so smooth out the behavior, i.e., regen should be slightly lagged and should then be applied smoothly, so that changing directly from propulsion to coasting or vice versa does *not* trigger max regen in between.

Does this make sense to you?

Volker.Berlin | 23. November 2011

In BMW's words (emphasis mine):

[...] The electric drive also allows for deceleration by means of the accelerator pedal. After the driver eases up on the accelerator, the electric motor acts as a generator, converting the kinetic energy into electricity which is then fed back into the battery. Energy recuperation generates a braking effect which makes a significant contribution to vehicle deceleration.

A coasting mode makes this unique "single-pedal control" of acceleration and braking using only the accelerator even more user-friendly. When the driver eases off the pedal, the electric motor's zero torque control keeps the drive train disconnected as long as the pedal is in this position. The vehicle now coasts without consuming power, driven by its own kinetic energy.

Timo | 23. November 2011

I would believe that your suggestion does not work, but BMW implementation does. They apparently have separate "coasting mode".

What you suggest would cause crashes in city traffic. You lift off your feet to regen and when car in front of you starts to get closer you lift it a bit more and hit the coasting (IE leg no longer causes pressure in pedal) and suddenly car does not slow down anymore.

Human reactions are too slow to prevent accidents there and your first reaction (press a accelerator a bit more to hit regen) might cause car to accelerate instead of decelerate and accident is ready.

It would be d*mn confusing to go from max regen to no regen.

Volker.Berlin | 23. November 2011

I would believe that your suggestion does not work, but BMW implementation does. They apparently have separate "coasting mode". (Timo)

Something went wrong communication-wise. I apologize. To be entirely clear: I wanted to suggest the concept precisely as outlined by BMW.

At first I had only the German text available so I tried a translation myself. Two sources for error here: Obviously, my translation, and less obvious but undeniable, the possibility that I do not fully understand BMW's concept.

That said, I had the same concerns as you when I first read about it, but thinking about it my first reaction would be "hit the break pedal", not "hit the accelerator pedal to slow down quickly". Seems safe enough to me.

The logic supplement to this concept would be to make the break pedal trigger regen, too. It all sounds very complicated, and it certainly is, implementation-wise, but if done right I expect it could all appear very simple and natural for the driver (and thus would be safe).

Mycroft | 23. November 2011

I agree, that would be a horrible implementation. When I lift my foot off the pedal, it's only because I want to slow down or my foot is headed for the brake.

I do want max regen on the accelerator pedal. Like you said VB, that allows for one pedal driving most of the time, except when either coming to a complete stop or for an emergency slow-down.

In the latter case, the max regen is a great safety boost since max regen is slowing the car already, before your foot even makes it to the brake. That shortens the emergency stop distance considerably!

EdG | 23. November 2011

I like the idea of having the regen level controlled by the foot.

Previously, I had suggested that the amount of regen be programmable, and, further, that an app be available to attach to a steering wheel function to allow control. Hold an "increase" rocker bar to increase regen, "decrease" half to lower it.

It could be implemented as an overload (reuse) on the same switches that operate the cruise control, a system that would not be in operation when the car is slowing.

The predefined level of regen would kick in each time, but the rocker switch could increase or decrease that level until the brake (or accelerator?) was operated.

I still like that idea, but if it can be implemented with the accelerator pedal instead, all the better.

Volker.Berlin | 23. November 2011

So Mycroft, I understand you would not miss "real" coasting at all?

I coast a lot (when driving a manual shifter), typically with my foot hovering over the break pedal. For instance, as soon as I notice that I cannot make a green light, I stop accelerating and switch to coasting, but I do not want to slow down much in advance of the traffic light, either, because traffic is dense and if I slow down too much someone will make a (dangerous) attempt to pull into my lane just in front of me.

In this situation, it would be ideal to control the amount of regen with the break pedal rather than the accelerator pedal. The prerequisite for doing so is that the accelerator pedal does not apply any regen when I lift my foot completely off.

Volker.Berlin | 23. November 2011

I still like that idea, but if it can be implemented with the accelerator pedal instead, all the better. (EdG)

Have you driven the Roadster? I am not entirely sure that I correctly understand your suggestion, but it seems to me that the Roadster has it implemented precisely like that.

Mycroft | 23. November 2011

I'm not sure if I would miss it or not, but I think I could get used to "coasting" to a stop by backing off on the pedal to a touch of regen. I'm thinking I would feel more in control.

My brakes would last a long time! My rear tires, not so much. :)

Robert.Boston | 23. November 2011

Volker, it seems like the genesis of your suggestion is that the "true coasting" on the Roadster is fine line. Isn't the obvious fix simply to create a bigger coasting zone on the accel pedal? Actually put a dead-band in the middle, where you have a few millimeters of coasting (push harder, you accelerate; push less, you regen).

Volker.Berlin | 23. November 2011

Robert, thanks for your suggestion. You are an alert reader.

If I remember correctly (from a 20 minute test drive), the pedal in the Roadster is trimmed such that there is a very smooth, continuous correlation between the pedal travel and the acceleration/deceleration. Without some practice, this makes it hard to feel where the "coasting" point actually is, but I think, that's a good thing. Usually, I simply want to determine speed or acceleration/deceleration. I don't care if that propulsion or regen or coasting is necessary to achieve it -- just give me the speed/acceleration I want. The Roadster's acceleration pedal does an admirable job at this.

And then there are opportunities where the actual speed is not so important to me and I can or want to make conserving energy my top priority. In these cases I want to coast/sail, maximizing the distance traveled at max efficiency (i.e., with neither propulsion nor regen), regardless of how much or how little deceleration that implies.

Thus is different situations -- depending not only on traffic but also on time pressure, mood of the day, and the available-to-required-range-ratio -- I have different priorities. I am looking for a configuration that seamlessly and effortlessly supports both without requiring me to explicitly switch modes or configure options. I think that BMW's concept may be appropriate, a sensible extension of what Tesla already implemented in the Roadster.

Kallisman | 23. November 2011

As far as I understand this is all a matter of coding, which means that they could make it user adjustable on the touch screen. You set up your own personal preferences, and the car loads them every time it recognizes your key in the drivers seat.

Personally I'm sceptic to the bigger dead band on the accelerator pedal. It would make it a bit hard to keep a steady speed if the road goes up and down, cos you would need to move the foot a lot over the dead band. But this could also be user adjustable.

Kallisman | 23. November 2011

They could just make a coasting button on the back of the steering wheel that u push when u want to coast. If u push the break or accelerator after that, the coasting mode would end.

I think finding the coasting point of the accelerator pedal is like using a clutch. A matter of practice.

Volker.Berlin | 23. November 2011

They could just make a coasting button on the back of the steering wheel that u push when u want to coast. If u push the break or accelerator after that, the coasting mode would end. (Kallisman)

I think that could work for me although I still believe that BMW's idea beats yours in simplicity and elegance.

I think finding the coasting point of the accelerator pedal is like using a clutch. A matter of practice. (Kallisman)

Except that the better you get at using the clutch, the shorter you will use it, usually only for a second or less. In contrast, when coasting you want to stay in that state as long as possible.

ggr | 23. November 2011

I'm a roadster owner, and I have to say I find much of this thread confusing and sometimes surreal. The "power control pedal" (there have been many discussions of what exactly to call this) works beautifully and smoothly; anyone who's driven a roadster for more than 10 minutes in traffic has fallen in love with it.

Coasting is a concept that is made necessary by internal combustion engines. Personally I see no reason at all to coast in a Tesla. We've all spent lots of our driving years learning to have our foot in the right position to get the desired speed or acceleration (or now braking), unconsciously moving it as we get to a slight hill or the traffic in front slows a little. Why would you, as someone above said, want to be in coast mode with your foot hovering over the brake pedal?

I agree with the people who say it is insane that lifting off the pedal entirely should cause coasting. If you look at the US NHTSA reports about braking in the Prius, there are reports that sometimes as the brake transitions between regeneration and real brakes, it stops braking momentarily! Some accidents have been caused by this. You don't want discontinuous behaviour.

Large trucks have, for many years, had pretty much the behaviour of the Tesla; when the driver backs off the throttle past the point of normal engine braking, it engages "compression braking" (mucks with the valves somehow to cause even more drag from the engine). Truck drivers love it because it is much less stressful and less work for them.

Anyway, my conclusion is simple: trust Tesla to (mostly) get it right. If the regeneration is adjustable, I for one will set it to maximum and leave it there, and trust my foot to regulate it well. I say "mostly" above because there are a couple of glitches. When you cancel cruise control with the button, you get a braking action unless you have tried to match the power pedal first, and if you hit bad bumps while decelerating sometimes the traction control cancels the regen and it can be surprising.

jbunn | 23. November 2011

I'm hoping for user config. The way I look at it, is the "accelerator" is called the accelerator for a reason. It's not an "accelarator/coasting/braking pedal depending on how you twiddle it with your big toe" pedal. Right next to it is the brake pedal. I'm hoping that obvious function won't change much. If I have to shift my foot off the accelerator pedal for a moment, I don't want the car to start slowing, and I would prefer to not have to hit steering wheel buttons to overide.

I'll probably set it similar to an ice car to just give me a gentle slowdown with foot off the pedal.

And I really do hope the S regens when braking, not just when not accelerating.

Volker.Berlin | 23. November 2011

ggr, thank you very much for your comment, which is worth much more than any theoretical discussion!

Coasting is a concept that is made necessary by internal combustion engines. Personally I see no reason at all to coast in a Tesla. [...] Why would you, as someone above said, want to be in coast mode with your foot hovering over the brake pedal? (ggr)

The only good reason would be to conserve energy. For me it also seems natural and convenient, but that may be a reminiscence of ICE driving which I will possibly loose once getting used to the Tesla way of driving.

EdG | 23. November 2011

And I really do hope the S regens when braking, not just when not accelerating. (jbunn)


Whatever regen is in place when slowing down should probably continue if you move your foot to the brake pedal. If some feature removes the regen when your foot is off the "power control pedal" then it will probably also stop regen from occurring during braking, which seems a waste and less safe (longer brake distance).

Is there a situation where regen should not be engaged during braking? Or is there a reason why regen is never engaged during braking? Otherwise it would seem a simple thing to allow the regen to continue always until you give the car more power.

dborn | 23. November 2011

Having test driven the roadster, it takes all of about 10 mins "learning curve" before you "get" it. It was one of the best features, i found, other than the massive and immediate "thrust back into the seat"!! One of the major advantages of regen as fitted to the roadster, is that your wheels will stay clean of brake dust, and you will probably never need to to change your brake pads (if you drive the car in a sane fashion). I really can't see what the controversy is in this regard. Brake lights come on so no issues there (better than in my current Merc which only has brake lights when actually braking. Guys, wait to drive the actual vehicle before getting so fired up!

michiganmodels | 23. November 2011

I agree with @dborn. After driving a Roadster, I found the regen braking to be a huge advantage.

Volker.Berlin | 23. November 2011

@dborn, @michiganmodels. Funny. In my posts above I explicitly state that I have driven the Roadster and that I like its implementation of regen. There is little to none controversy on whether or not having regen on the accelerator pedal is a good thing.

All I noted was that BMW took the same approach, and took it one step further. I still think there may be something to it, but from the discussion here I learned one thing: It (the discussion) is entirely in vain. Seems that this kind of things cannot be discussed unless you have actually experienced it in practice. So we must rely on Tesla to do the experimenting and testing for us, and hope that they come up with the best possible solution.

The Roadster is very promising, but if you think that it cannot be improved, then you are stuck.

Brian H | 24. November 2011

A test drive and long-term use are different beasts. When your body picks up the automatic software adjustments to exploit the system, that's when you can judge its value.

Brian H | 24. November 2011

In physics terms, acceleration is any change of vector (direction or speed).

Besides, it's called the "goose" pedal.

Mycroft | 24. November 2011

@VB: "I still think there may be something to it, but from the discussion here I learned one thing: It (the discussion) is entirely in vain."

I agree that there may be something to it. I disagree that the discussion is in vain. For one thing, we have to talk about *something* while we wait for our cars to be built. For another, I hadn't thought about coasting too much with regards to the regen braking.

I'm still not sure what BMW's implementation is, but since our discussion, I've been thinking about it. I think someone might have mentioned it earlier, but I think an automatically adjusted, very slight indent in the pedal's travel might work.

So, as you're accelerating or maintaining speed, the pedal is calling forth the juice. Then you let up on the pedal and you feel a very slight indent. This indicates that you're coasting. As you let up a little more, you're out of the indent and you are regeneratively braking.

I'm thinking that that implementation would definitely work for me!

Timo | 24. November 2011

@EdG, as far as I know Tesla does regen whenever your foot is not in accelerator pedal, so in braking you are doing both, max regen and braking (otherwise that would feel really odd).

Only way to not do that is that you press accelerator at the same time you press brake.

Problem with regen is that it only affects rear tires, so it can't be extremely powerful, otherwise you might lose control of the car. You would need to have engine at the front tires too to implement so powerful regen that normal brakes do not get engaged at all.

Also normal brakes are required by law in many places, so no matter how reliable regen you could get you would still need to install those, and connect them to brake pedal.

I think Tesla implementation is about as good as it could get, especially with user adjustable regen level.

EdG | 25. November 2011

Thanks for that, Timo, simple and effective. I'm not very clear on the control system that, as little as I understand, ensures no slippage on acceleration or regen. From what I've read, the control of the wheels that gives us the equivalent of a "limited slip" system comes almost "for free" with an EV.

With that system in place, I imagine even a lot of regen on the rear wheels wouldn't cause a loss of control.

Too much braking in the rear is bad?

Not enough because the regen is strong and the driver isn't pressing down enough? Then the driver just brakes harder.