May 7, 2016
LectrikPower So in pondering my option choices I am leaning heavily towards single motor for my MIII. I would rather spend the money on SC, AP and cold weather packages.
Other than the obvious traction and performance enhancements that AWD gives, is there an efficiency difference between RWD and AWR for a tesla? Is it better to run a single motor at a higher workload or two at lower? I think I remember something about the front motor not being used during highway driving on AWD S's?
My apologies if this has been covered to death. I did search the forum first and mostly got threads on TSLA stock. Thanks
�
May 7, 2016
Craig9080 70% of braking force is generated by the front axle. With a single motor M3 you will be wasting all of this as heat on a traditional brake disk, with a D you will be able to recoup some of it. Also, the regen will be much better as it will feel a lot more like traditional braking as opposed to a [not-so] gentle E-brake tug. I'm sure the Model S owners can chime in as to actual numbers.�
May 7, 2016
mspohr With the model S, the dual motor versions are about 5% more efficient. A small improvement but if you also consider the better handling and performance, it could tip the scales for you.�
May 7, 2016
Jason Bourne IIRC, in a dual motor Tesla, each motor has different performance and efficiency curves. For example, the front motor is better at top speed but the rear motor is better at acceleration - so the software leverages those benefits in management operations of the car (this is just an example and possibly not factually correct, but this concept is my point).�
May 7, 2016
JeffK For Wisconsin and anywhere that snows I'd recommend AWD for safety's sake. If it's less than $5K extra and you have at minimum a year and a half to save for it, I'd say try to make it work.
Sure you can get by with RWD, but why? Do you plan on anyone else driving it?�
May 7, 2016
DFibRL8R The regen braking with a single motor is pretty robust even for a car as heavy as the Model S. I have a single motor and I rarely use my friction brakes (really just emergency braking and upon final approach to a stop the last few yards). Thus I don't see the additional motor having a great benefit in terms of efficiencies in braking in typical use. The improvements come in with power output where there is a more efficient use of 2 motors in tandem than a single motor (something about torque, sleep etc, I'm not an EE so I'll leave the technical particulars to someone else!)�
May 7, 2016
LectrikPower I can see how that would work with software computing best efficiency. Thanks.�
May 7, 2016
LectrikPower Yes, my wife will be driving it as well. She is an excellent driver
For reference, my 02 Mazda Protege5 was the only car we had for a few years. Granted it was front wheel drive but it has no ABS or traction control and a manual transmission. She commuted 40 minutes each way year round rain sleet and blizzard and did great. I'm not saying it was ideal but she is a pro. Our Kia Serento is front wheel drive but it is an SUV and has ABS and decent traction control? Obviously AWD would be better but I'm not convinced it is totally necessary.
I will have to see what the final price difference will be if I go with the D. Like I said I would rather spend the money on the other options. Maybe I can have it all, we shall see.�
May 7, 2016
e-fit Has anyone compared the Telsa S AWD vs RWD? I currently drive an i3 and the one thing I don't like is that when you are using regen, and come into a tight corner, the regen can reduce or stop altogether (especially in the wet) to prevent the rear wheels dragging. For me just that on its own is enough to want me to go AWD, thought I'd want to check it will actually do what I want first!�
May 7, 2016
Mkorpal Based on what what Tesla states on their website for the S, duel motors adds 6 miles of EPA range, and reduces 0-60 times by 0.3 seconds. Not to mention better handling. Considering Tesla is charging 3 grand for a 15 mile increase in range, and we know the duel motor on the 3 will be less than 5 grand (I think it will be 4 grand most likely), I'd venture to say that duel motors will be the most no-brainer option on this car.�
May 7, 2016
Kandiru Given your geographical location dual motor is the only safe choice. Coming from Quattro I can confidently say the Model S AWD is excellent, mixed with Michelin X-Ice X-Green low rolling resistance (less energy use) tires winters are a breeze here in Ohio.�
May 7, 2016
Garlan Garner Whatever Ludacris comes with....that's what I'm getting.
I suppose that would be Dual Motor. right?�
May 7, 2016
jerry33 Note that the efficiency gain is for highway travel. Stop and start driving will be less efficient. Frunk space is also lost. Either of these may or may not be important to you.�
May 7, 2016
Zoomit That's certainly the case with the S/X, but not a given with the 3. They may opt to have a single frunk size and leave the RWD cars with unused volume between the axles.
Having said that, it does look like the frunk could expand rearward based on this picture.
![[?IMG]](https://electrek.files.wordpress.com/2016/04/model-3-frunk.jpg?w=1000)
�
May 7, 2016
Garlan Garner You guys really care about frunk space?�
May 7, 2016
Zoomit I don't know. I've never had a car with one. It might be easier to store and get to certain items from the frunk than the trunk.�
May 7, 2016
jerry33 When I go on trips, I just lay my pants and shirts and their hangers down in the frunk. The small items go in a bag. No suitcase necessary and I only need to take the bag, shirt, and pants into the room where I'm staying. So yes, I care about frunk space.�
May 7, 2016
Garlan Garner lol - If its so close of a trip....lay your stuff down on the back seat.�
May 7, 2016
LectrikPower Well I don't know about "only safe choice" but I know it would be better�
May 7, 2016
jkk_ I've seen reports that with the "facelifted" S the frunk space is also lost for RWD cars. Apparently the space is reserved for the HEPA-filter even if you don't have it.�
May 8, 2016
Hayden Is it possible to disable the engine in front with dual motors?
I like rear wheel driving from time to time.�
May 8, 2016
jerry33 And have the car broken into. Thanks, but no thanks. Typically my trips are 7-14 days.�
May 8, 2016
jerry33 No, other than what the car might do automatically.�
May 8, 2016
mspohr Can't do that since I throw all my fast food trash there.�
May 8, 2016
dgpcolorado Well, yes. I rather like the extra frunk space and on long trips I will be using it to carry a spare tire, since I prefer to be able to self-rescue when I am very far from home or a city.�
May 8, 2016
Garlan Garner LOL..�
May 8, 2016
Garlan Garner
I forgot all about the spare - or the lack of one.�
May 8, 2016
rv1458 yes, you can. The Model S allows you to software select different versions. For example if you have a P90D you can select the 70D, or just the 70. The car will then limit the performance so that it drives like that lower model. Unfortunately it does not work the other way around ;-)�
May 8, 2016
Garlan Garner That's interesting. I would never have thought that Tesla would do something like that. Hmmmm
Why would someone pay all that money for extras....and then downgrade through software?�
May 8, 2016
rv1458 See this link: https://teslamotorsclub.com/tmc/threads/what-does-this-do-holding-t.67987/�
May 8, 2016
rv1458 I think it's mostly intended for the sales people so they can simulate different versions you're considering. However, the ability to switch between RWD and AWD would be nice for the reasons posted in the original question.�
May 8, 2016
timk225 On the S, with single motor, what was the 0-60 difference between the 60 and 85 batteries, before the performance and D and Ludicrous options became available?�
May 8, 2016
Lunarx Thanks for pointing this out.
I was trying to take the purist approach and save the weight of an extra motor (and bigger batteries), however front re-gen is too good of a thing to miss-out on.
Not just because of the added charge recovery, but because it will minimize using friction brakes in front.
All the other advantages of AWD usually do outweigh the weight increase.
Now you convinced me that AWD is a must-have option.
I just hope under-steer is not an issue.�
May 8, 2016
Lunarx Seems like a manipulative sales tactic.
I imagine the real 70, which is 500lb lighter than a 90D, would represent itself better than a software neutered 90D would.
Although, for non-up-sell purposes, it is cool to have the choice to select RWD mode.�
May 8, 2016
Booga I think teslabj0rn was using a RWD tesla in Norway and didn't complain about it.
To be frank... I'm torn on the awd myself and largely due to price. I want the same upgrades you do, but I'm concerned that if I add all wheel drive, the 35 base turns more into 44, then doc and delivery brings it to 45, and then sales tax can bring it up to 48-49. That's an expensive car! If the full federal tax credit is still there, great, it'll come down a little to 41 or so.
Without AWD, I'm thinking it might be closer to 38-39k.
For me, I won't get this car without a range upgrade or autopilot. The winter package is minor in cost so I'm not concerned about that. I'm hoping the price of awd, autopilot, and range upgrade is significantly less than the premiums they charge on the S.
If it's not, there's a chance I'll cancel my order. The 215 miles of range just won't cut it for me. I need 300+.�
May 8, 2016
melindav @Lunarx I don't know that the RWD saves that much weight over AWD. The 'standard' AWD uses a smaller rear motor than the RWD motor motor. It's not until you jump up to the PxxD that the rear motor is comparable to the RWD motor.�
May 8, 2016
Zoomit But...that first statement is not true. An EV with RWD-only will regen with the back axle until the desired braking effectiveness is insufficient and you need to use the friction brakes. Regen maxes out well below the deceleration possible with only the rear tires, under most conditions. Besides the Model S, the i3, smart ED and i-MiEV have all used RWD regen. For any given deceleration rate and under most conditions, a RWD will regen with the same efficiency as a FWD and AWD.
It is definitely true that dual axle regen will be more stable and consistent. I've read that i3's will reduce regen in wet conditions to keep the rear tires from skidding as part of stability control.�
May 8, 2016
Zoomit S 60 4323 lb from 2014 Tesla Model S 60 - Instrumented Test
S 70D 4608 lb from 2015 Tesla Model S 70D - Instrumented Test
I'm not sure how much the 70kWh battery added, but that difference is 285 lb. If it is ~200 lbs in the Model 3, that will make a difference in how it handles. (as will the AWD: possibly good, possibly bad.) The 3 xxD will be more efficient however.�
May 8, 2016
JeffK Zoomit are you sure about the RWD regen thing... last time I checked there's much higher torque at the front during braking as the weight of the car shifts forward... Also with a smaller motor up front, this increases the efficiency of the regen due to higher load. A large motor on the back can't get the same regen efficiencies due to far less load.
It's the same reason older traditional cars had disc brakes in the front and drum brakes in the back.
Here's an article on the matter as well BMW i3 versus Tesla Model S 70D�
May 8, 2016
Zoomit Sure? Yes. Think about it this way, if you lost your front brakes in an ICE vehicle, could you stop? It would no problem in most cases. Max braking deceleration is typically over 1g eyeballs out. Max regen peaks only around 0.3g. Can only the rear tires create that deceleration? Absolutely. With the relatively light braking forces created by regen, a rear motor can extract the kinetic energy just like a front motor.
This is true as long as the rear tire can create ~0.3g, for example. As that article said, "[the 70D] should be less prone than the i3 to traction loss during difficult braking conditions."
While I don't know how the efficiencies change when the braking load is split between two motors, I don't think it's significant. Remember, most EVs are FWD and have very efficient regen. Of course the most efficient car, the i3, has RWD regen.
Creating maximum brake force is completely different and that's where the ~70% number come in for front brakes. This is due to the vehicle's inertia creating a moment on the front wheels and a higher vertical force. That higher vertical force creates greater tire friction and allows greater braking force to be applied to the tire before it starts skidding. Hence bigger, more capable brakes are on the front axle.
So regen efficiency should not be a discriminator when choosing between RWD and AWD. Regen braking feel and stability are something to consider, especially in marginal traction conditions.
In an ICE vehicle, AWD only accelerates you quicker. It does not slow you down any better. (Arguably it slows you down worse due to the additional weight of AWD.)
In an EV, AWD accelerates you quicker and also provides more stable regen braking than RWD.�
May 9, 2016
LectrikPower I'm with Booga. If I can get SC, AP, cold weather and AWD that would be great. I may drop the AWD to save money.
Base range will be good for me. Will have to see if they do option bundling. That may throw a wrench in the works.�
May 9, 2016
eisbock At the reveal, Elon said they were able to shrink the car by moving the driver forward (since there is no engine). I'm not sure if this means you'll sit closer to the windshield or what, but it does explain why there appears to be unused frunk space. It's for your legs now! And that means it's unlikely the frunk can be extended back toward the driver.�
May 9, 2016
Lunarx Is Tesla under-utilizing regen, because it would be awkward to have full regen with Single Pedal Speed Control?
In a RWD, full regen on throttle lift, would be the equivalent of Drift Mode.
Is the article right that, the Tesla brake pedal is friction only?
I would find that dissapointing, as I really like blended braking (as per the Volt).
I hope these things are software setting choices.�
May 9, 2016
garsh The amount of regen is controllable via an option. I know the S allows a lot more regen than a Nissan Leaf. Sorry, I don't know where a Volt lies in that range.
That's my understanding.The Leaf also has blended braking. I think this is a mistake. It's a more complicated system. It also means that the brake pedal feel differs depending on the amount of regen available (ex - charged to 100%, and there is NO regen available).
I think Tesla made the correct choice here - offer a relatively high amount of off-pedal regen, and have the brake pedal control only the friction brakes.�
May 9, 2016
Zoomit I wouldn't say they're under-utilizing regen. Remember "full regen" is pretty light compared to aggressive use of friction brakes. Lifting the throttle going into a turn hot would induce oversteer, if the traction/stability nannies didn't intervene. "Coasting" (no accel/decel from the motor) requires partial throttle pedal, like when an ICE car is reving high and you want to avoid engine braking.
The S/X brake pedal is friction only, which I expect they'll carry over to the 3. I dislike blended brakes and am hopeful they keep them separate.�
May 9, 2016
Dan Detweiler I have driven a Volt for four years and that was the first thing I noticed about the Model S when I drove it. There is a lot more regen braking in the Tesla than with my Volt.
Dan�
May 9, 2016
dgpcolorado My general impression is that you are overthinking these things. Tesla has fairly strong regen � yes, even with "just" RWD � that allows for single pedal driving. On a typical trip, the only thing I use the brake pedal for is to start the car and to hold it stationary at a stop light. Otherwise all of my accelerating or slowing is done with the "go pedal", even brief stops at stop signs unless I have to wait for traffic.
Unless the battery is quite cold or nearly full, and regen is limited, the Tesla regen is strong enough to slow the car to nearly a stop when going down a steep hill (which is much of my driving here). The friends who have driven my car area amazed by this.
Single pedal driving is quite intuitive in my experience and one rapidly becomes accustomed to it. After which, going back to any sort of regular car seems like a major step backwards. Having driven a LEAF for years I definitely do NOT want to go back to blended regen on the brake pedal; I'll stick with single pedal driving.
You really need to take a test drive in a Model S and your concerns will be alleviated.�
May 9, 2016
Lunarx Volt does have a Low Mode which is similar to single pedal speed control (like Tesla), but I guess it's less agressive on regen.
Volt has added paddles to increase regen on-demand.
However, neither is needed, because the brake pedal engages regen.
It works real well and is completely smooth.
The -kW reading confirms regen is happening vs friction braking.�
May 9, 2016
Lunarx There are some mixed impressions on Tesla Regen.
One impression was that it's not strong enough to justify having it on the front wheels [AWD].
Another is that Tesla regen is beyond what any other EV offers.
I gather that Teslas lift throttle regen is more than adequate for normal driving.
However, I suspect it is dialed back, to keep it safe.
I cant believe people could handle 100% regen on throttle lift.
Thats why, I would like to see regen on the brake pedal, as its easier to modulate the full range of regen that way.�
May 9, 2016
dgpcolorado This simply isn't true. Tesla regen is modulated just fine on the accelerator pedal and is speed dependent, just as one would expect. Enough regen to slow the car to a stop going down a 14% grade isn't enough for you?
But until you actually try the Tesla version of regen there isn't much more I can say. Don't knock it until you try it.�
May 9, 2016
JeffK As a prius owner I say regen integrated into the brake pedal stinks... the hand off to the physical brakes is clunky, it's more complex to manufacture, in a Prius there's a messed up acceleration feeling when braking over a bump and the car jumps forward a few ft (read: dangerous).
With regen in the accelerator you can do one pedal driving which is super convenient.�
May 9, 2016
David99 I think there is some confusion about dual motors being more efficient than single. The single motor Model S has the large motor and drive unit that was originally developed. Later, Tesla designed the smaller and slightly more efficient front motor and inverter unit. It's not different gearing. It is just that the newer, smaller motor is a little more efficient.
Dual motor Model S have the small motor both in the front and in the back. The PXXD versions have the old large motor in the back and the smaller newer in the front. The PXXD can switch off the back motor when cruising and running just on the smaller motor. They call that torque sleep.
It's not gearing that makes it different, it is not running two motors instead of one. It's just the more efficient smaller motor that makes the difference. In general, the type of electric motor Tesla is using runs more efficient at higher load than partial load. Having two smaller motors has the advantage that you can accelerate fast and efficient using both motors at high load, and when cruising, you switch one motor off so the load on the other is higher making it more efficient.�
May 9, 2016
LectrikPower So regen will occur at "throttle" settings other than zero, meaning at less than the position needed to keep your speed steady regen will occur? Is that right?�
May 9, 2016
Booga That makes me hopeful the cost to go to all wheel drive may not be too much. Two smaller motors, that don't need to be nearly as capable as higher powered ones, might not be too much more expensive. I would like all wheel drive but it'll be a lower priority for me. There are times it's helpful and a little added range from more regen is always welcome.�
May 9, 2016
JeffK Yeah, like engine braking if you've ever driven stick.�
May 9, 2016
Booga Speaking of two motors... What about 4 motors at some point? You could then get more individual wheel control, right? Wouldn't that allow for better handling and even turning? (If you weren't concerned about the rubber on your tires, you could turn the car 360 degrees without actually turning a wheel.)�
May 9, 2016
LectrikPower Got it.�
May 9, 2016
AZ Desert Driver don't you need two sizes of spare?�
May 9, 2016
Lunarx I agreed Tesla Single Pedal Regen is effectively enough (even if it's softened up).
My question remains, is it 100%?
Can the Tesla gurus to enlighten me as to the % of Regen Tesla achieves?
How can regen be anywhere near 100% w/o use of Regen on Front Wheels [AWD]?
Does stability control kick-in and engage front friction (to balance 100% RWD Regen)?
Just because Prius mucked up blended braking, does not mean it stinks.
If Volt can do blended braking perfectly, Tesla could too.�
May 9, 2016
gregincal 100% of what? Regardless of anything else, max regen power will always be a fraction of max acceleration power, because batteries cannot absorb power nearly as quickly as they can supply it.�
May 9, 2016
Alketi Would there be any value in adding a steering wheel paddle that acts as a brake, but really modulates the regen? You could just about remove the disc brakes from the maintenance list, if done correctly.
Also remembering that Musk mentioned how the production steering wheel would be far more advanced than the prototype.�
May 9, 2016
JeffK Regen can only ever be on the same axle as the motor. I could be wrong but I believe the negative torque is monitored and controlled without front brake engagement. (Unless you actually hit the brake)�
May 9, 2016
David99 There are different losses. The motor and inverter can be seen as one unit as they only work together. They are about 90% efficient, but driving and at regen. The battery also has about 90% efficiency. So very roughly when you regen, you get about 80% of the energy back as usable in the battery. Now of course the car still has rolling resistance and wind drag and many other losses. All of these apply when driving as much as when regen.
What wheel is connected to the motor when doing regen is not important. If all you do is use the motor in regen mode to slow down the car then all of the kinetic energy that is available gets captured back (minus the losses). Having RWD doesn't mean you loose a certain percentage of possible regen at the front wheels. They don't do anything, they are not slowing the car down.
I think some people are confused when they read about the front/rear brakes contributing 70/30% when slowing down. That's how the brakes are designed, but has nothing to do with how regen works.�
May 9, 2016
jerry33 Regen can only capture some part of the kinetic energy at the time the regen braking is started. (Obviously, that's far less than the amount of energy used to accelerate the car to that point as much of the power has been used to overcome air resistance and drag from the drivetrain.) V0------>V1------>R1------>R0-->V0 The car starts at V0 (stopped) and accelerates to V1 (cruising speed) it travels some distance and then needs to stop. Regeneration starts at R1 and continues to R0 where regeneration cuts out. The power used between V0 and R1 is immaterial as only the kinetic energy at R1 is available as potential regeneration.�
May 9, 2016
JeffK Physics disagrees with that statement. Weight pushes up front during deceleration which leads to a higher normal force and more torque on the front axle, if spinning a generator, more torque = better. You'll have higher energy capture from the front vs having it only in the back.�
May 9, 2016
David99 There is zero torque on the front wheels if you only use the back wheels to slow down or accelerate.
What you are confusing it with is when you brake all four wheels, the weight shift causes the front wheels to have more traction thus you can apply more force on the front wheel brakes. That's what the front/back brake ratio is allowing more force on the front brakes. But again, that has nothing to do with applying negative torque to only the back wheels. By your logic the front wheels would slowing down the car on it's own. Physics disagrees with that�
May 9, 2016
JeffK So you're saying if you have two equal motors one is on a FWD car and another is on a RWD car, that the FWD wouldn't capture more energy???�
May 9, 2016
Lunarx 100% of what is capable.
I can get -60kW of regen (peak) on the Volt.
(Typical sustained is around -25kW +/- 10kW)
Seems like if I hit the brakes hard enough, to exceed -60kW, it goes to full friction.
That's 3.3C of Regen (at peak).
For a Tesla w/ a 60kW plus battery 3.3C would be 200kW regen.
That is double my full acceleration.
So what are you guys seeing on -kW under Regen?�
May 9, 2016
gregincal I'm not sure what the amount of energy has to do with it, since you can accelerate really gently but try and come to a really sudden stop. My point is that the Model S battery system can provide up to 500kW of power during acceleration, but if you tried to design a regen system that generated 500kW of braking power you would fry the battery. The Tesla regen has a max of 60kW of power. Although the supercharger can feed more power into the system at lower states of charge it's undesirable to have a regen system that always provides differing amounts of available braking power. At 60kW they only have to limit regen braking if you are at the upper end of a range charge.
In other words the battery is limiting factor for regen braking, not the physics of braking.�
May 9, 2016
stevezzzz Back in the early S days, it was explained that regen was programmed to provide a constant 0.1g deceleration, with a limit of 60kW. At roughly 45mph and slower, you get the full 0.1g of deceleration as soon as you lift off the go pedal. At higher speeds, the 60kW limit kicks in and you won't have the full 0.1g of deceleration until the car slows down (to roughly 45 mph). Things are different now, with the Model S dual motor variants and the Model X; I haven't really studied what's going on, but to my uncalibrated tush the X has significantly stronger regen compared to even the dual motor Model S variants.�
May 9, 2016
David99 Correct. It makes no difference. Now, when pushing things to the extreme, the front wheels have more traction and you could apply more negative torque to them before the start to lose grip. But when talking about regen on an EV we are not anywhere near that level.�
May 9, 2016
JeffK sigh�
May 9, 2016
Craig9080
Engineers doing the ride-alongs at the reveal referenced differing efficiency bands for the motors on the M3. Your references are dated and incorrect.�
May 9, 2016
Craig9080
The problem is that you still have weight transfer - hence the 70% is inescapable...because physics. Go ahead and disconnect the front brakes on someones car and see how long it takes them to put it into a ditch. Without the aid of any friction brakes the effect on vehicle dynamics is essential the same as a metered application of the E-brake. I do not disagree that you CAN brake with rear tires only but simply that it is a horrid solution for a performance car and greatly upsets the vehicle dynamics. Furthermore, after weight transfer during either an abrupt braking event (cut-off/short light) or a prolonged one (coming up on traffic on the highway) the application of rear brakes becomes increasingly dangerous.�
May 9, 2016
gregincal You are correct that in some theoretical system it of course could capture more energy. The point is that none of that is the limiting factor, it's the ability to store the captured energy in the battery. With that limitation anything about where you capture it is moot. So David99 is correct that in any current or foreseeable EV it will not make any difference.�
May 9, 2016
LectrikPower What about capacitors for regen capture? Would there be less loss using them? They could be used the next time you accelerate from low speed. Once they were charged it would go to the battery. Or is the complexity not worth it?
Someone made a racing motorcycle that had regen capacitors that would give an acceleration boost after heavy breaking.�
May 9, 2016
Lunarx Actually, David99 agrees with you "when pushing things to the extreme".
He just doesn't believe EV Regen is powerful enough to necessitate being on the front axle.
If it's true that Tesla regen is only -60kW, the rear wheels could probably handle all of that, w/o too much drama (considering Tesla's long wheelbase and 4300-4900 lb curb weight).
I appreciate all the information being shared here, it was very revealing.
I still suspect Tesla is sandbagging on Regen.
In which case, AWD seems less essential again.
This is the problem with having 2Y to research your car purchase�
May 9, 2016
voip-ninja The car is unlikely to offer 300 mile range at any price. The battery upgrade for it is likely going to be $7500-$10,000 so it seems it is already over budget for you.�
May 9, 2016
David99 The battery is not really the problem. It can be charged at a high rate and the charging efficiency is actually pretty good. In normal driving I never found the regen amount to not be enough. Capacitors would not have any advantage in terms of efficiency. Maybe in race situations where they might be able to capture energy at a higher rate. Maybe.�
May 9, 2016
Skione65 @David99,
Is the "Torque Sleep, or switching one motor off so the load on the other is higher making it more efficient" an 'automatic' operation sensed by the car speed or is something you have to manually shut off -and on?
Ski�
May 9, 2016
David99 There is no manual switch or control for it. The car does all of it on it's own. I believe you have to have 'Range Mode' turned on for it to be enabled. Tesla says it is seamless and so quick that you don't notice it. I'm a little confused why torque sleep is not enabled all the time. Maybe there is a disadvantage (that Tesla isn't telling us about) so they don't have it enabled it by default.�
May 9, 2016
Zoomit Just remember that the i3 has strong regen, RWD, a short wheelbase and is lightweight. It would be insightful to go test drive one and see how the regen effects vehicle dynamics. Just go into a corner and lift off the throttle and see what it does. I've never done this, and am not responsible for the result! However, you should be fine because of the stability control.�
May 9, 2016
Zoomit For those looking for a little more physics background on load transfer during acceleration/deceleration, here ya go!
�
May 9, 2016
David99 All good points. I have actually worked for BMW several years ago. They do very extensive testing in any possible situation before they come out with a car. I also know that BMW takes driving dynamics very serious.
I'm a little surprised about the concern with having just the rear (or front) wheels doing regen. Regen is always much lower than accelerating. When accelerating we have a much much higher torque on just the rear (or front) wheels and it does not affect driving dynamics much negatively. So why would the lower torque of regen be such an issue? I think we all agree having individually adjustable torque on all four wheels would be the ideal situation, but it's not like we have an issue with millions of RWD or FWD cars on the streets right now. What am I missing?�
May 9, 2016
mspohr sigh�
May 9, 2016
David99 That's all good. You are still confusing the weight shift with converting torque via the motor to electricity. Yes during deceleration the weight shifts slightly to the front wheels. But that doesn't mean the front wheels are contributing anything to decelerating the car. That is a completely different and unrelated thing. The energy needed to slow the car down does not change in any way. The kinetic energy (vehicle mass * velocity) is the same regardless of the weight distribution. There is a certain amount of kinetic energy that can be converted into electric energy. It doesn't matter if you use one wheel, 2 wheels, all 4 or have a trailer with a generator creating the regen. Weight shift just causes the wheels to have different 'weights' in different situations. It does not say anything about how much torque (negative or positive) is applied to a wheel.�
May 9, 2016
gregincal I agree that in normal driving it's enough, but for aggressive driving or reacting to unexpected events you need to use the friction brakes. I do think the 60kW limit is a compromise between what is "enough" regen and what is good for the battery (I do not believe it has anything to do with problems due to braking on the rear axle only). The amount of extra energy you could regain using capacitors for hard braking wouldn't be much for 99% of driving, certainly not worth the cost or complexity.�
May 9, 2016
Lunarx David99, the load on a tire drastically affects the friction of the tire and the amount of torque it can transfer to/from the ground.
So a loaded tire could generate more regen torque, provided the unloaded tire would loose traction, from the torque of regen.
During braking, rear tires unload and front tires load.
However, you state regen torque is so low as to not present an issue.
It seems, on that point you could be right.�
May 9, 2016
Zoomit To add a little, it's not that the torque is so low during regen, it's that the deceleration is so low during regen. Remember that the load transfer which unloads the rear tires is a function of deceleration. The 70% number that people reference is at or near max braking of ~1.0g. The deceleration g's for regen are <=0.3g, hence the load transfer is less than a third of the peak value seen during a panic stop. So during max regen the rears may unload 10% and the fronts load up 10%. As stated above, this light unloading is within the ability of the rear tire to maintain traction most of the time.�
May 9, 2016
Booga I disagree, but let's see. The standard calculation may not be applicable, because the cost of producing batteries will vary by multiple factors but one of those includes just how dense you want them to be. There is a lot of variability in batteries from manufacturing and so it allows for different pricing at different levels. The quality needed to achieve 100 kwh in a model s for example is very different from what they'll need for, say, 50 kWh in a model 3 or 75 kWh. That's why the regular upgrade for 10 marginal kWh on a model S is not a direct translation to the model 3.
If it really is that expensive, I would agree that I'm going to be priced out of this car. I'm super excited by the new technology but if it'll mean the target price with my options moves up to 50k or higher, it'll be something I'll begrudgingly walk away from.�
May 9, 2016
DrManhattan Not sure if it's been covered, but it appears Dual motors haven't had the problems single drive units have had. Either the dual motor is better, or possibly less stress on the drive units. Might be a reason to get it alone if they prove to be problematic out of warranty.�
May 10, 2016
jerry33 I don't really get this thread. There is only a certain amount of kinetic energy at any given speed that can be potentially captured. Capturing it faster would slow the car down faster, but wouldn't capture any more energy because there is only so much to capture in the first place. It might even capture less because the faster the rate the more will be converted to heat.�
May 10, 2016
Northrop �
May 10, 2016
Dan Detweiler We'll, there ya go...learned something today!�
May 10, 2016
garsh I think the main reason for limiting regen is the lack of anti-lock abilities. I know if I hit a bump on the road while decelerating heavily in my Leaf, the car will immediately cut back almost all of the regen while the anti-lock system is pulsing the brakes, and then stay in that state (no regen) until the brake pedal is released.
How does a Tesla handle situations where the anti-lock brakes kick on?�
May 10, 2016
Kristoffer Helle If you brake hard(almost locking a tire) it's turns of the regen. If it hadn't done this, it would destroy the "transmission" fast.�
May 10, 2016
gregincal This is isn't about whether the energy can currently be captured, it's whether the energy can be captured while driving like a maniac and braking hard.�
May 10, 2016
Northrop Very true. Regen is not of much use when you gotten used to driving electrics. The smaller the battery, the more important to not use regen as it's a waste. Looking at the video above you get only 50% back. (IRL might be less too, but the video says 50%) Better of not accelerating so much and save the full 100%�
May 10, 2016
AZ Desert Driver 0k....bottom line. do I order awd or rwd?
leaning toward awd, heavily, but the reasons are softening. Looks like resale may be more important than regen. hate to buy for resale.�
May 10, 2016
JeffK AWD is better in nearly every way, efficiency, traction, handling, torque vectoring, acceleration, more even tire wear, stability... and it's not a lot more cash.�
May 10, 2016
Zoomit I'll disagree. If you're hypermiling, that's an atypical scenario where the losses of regen should be considered. For normal driving though, regen is critical to the overall efficiency of electric vehicles.
You cannot interpret that video to say that regen is only 50% efficient. Some of the kinetic energy at the peak speed is lost from aerodynamic and tire drag forces during the deceleration and hence is unavailable to be recuperated by the motor into the battery. When considered independently, I understand regen is closer to 80% efficient.�
May 10, 2016
Zoomit You should get AWD, because Tesla needs the profit and it doesn't cost me anything.
More seriously, I'll repeat what I said up-thread, "Regen efficiency should not be a discriminator when choosing between RWD and AWD."
This ^, understanding that only you can say if it's really "not a lot more cash".�
May 10, 2016
dgpcolorado The regen is also limited when the battery is cool or cold. I frequently have regen limited to about 30 kW, or a bit less, when my battery is cool, until it warms up a bit while driving. A cold battery might have little or no regen, even at a low SOC. It is something those of us in cold climates have to consider. Charging at the last minute warms the battery somewhat and can help with that.Just so!�
May 10, 2016
dgpcolorado I would greatly prefer AWD because it would help with getting up my steep curved driveway in winter (I have chains for my RWD S for the times the driveway is too slick to get up). This isn't something you would deal with in Tucson!
I'm guessing that AWD will be a $4000 option on the 3. Is it worth that to have somewhat better handling and efficiency (range)? Depends on your wallet and preferences.
My options list is pretty simple: 1) Bigger battery (likely includes Supercharger access if it's an option on the base model), 2) AWD. After that there isn't much that I'm willing to pay for. Much as I'd like a heated steering wheel � much more useful than heated seats � I'm not willing to pay $1000 for the cold weather package to get it. I have no use for Auto Pilot, given where I live, so I wouldn't pay extra for that.
No, my car has only one wheel size: 19 inches. I bought a spare wheel and had a tire put on it for use on long road trips (otherwise it stays home).
When it comes to buying new tires � my mountain driving is very hard on tires � I will buy three and use the one on the spare wheel as the fourth. Then I will put the best of the old tires on the extra wheel for use as the spare.�
May 11, 2016
Northrop No, for normal driving regen are a failure. Plan your driving and don't waste energy on brake/regen. You can do this without hypermileing to the extreme. It's just about chilling a bit, not driving aggressive.
As for regen efficiency you need to feed the car with power from the battery to get it moving, efficiency of 90%-ish. Then when braking with regen you are feeding it back to theb atter with efficiency of 90% at it's best? I doubt it's 90% as you see model S overheating way faster if regen are on. To this efficiency numbers you need to add tire traction, roll resistance etc. I think the 50% in the video are a good mean value to aim for. Again remember you first need to make the car moving with energy before you can regen it. Atleast the video is an IRL test and the best shoot at it so far.�
May 11, 2016
AZ Desert Driver just curious. does a spare fit in the frunk?�
May 11, 2016
jerry33 Depends. Not if you have any kind of "D". 19" tires can fit in non-D (this somewhat depends on your car because the size changed over time) but many folks aren't comfortable having something that solid in the crumple zone. Others have used a BMW space saver spare.�
May 11, 2016
dgpcolorado Sort of. It won't lie flat in that space if fully inflated. Others have said that it will if pressure is dropped to 35 psi but I haven't tried that yet. This is with the large frunk in a RWD Model S. I don't think that there would be any way to get a spare in the frunk of an AWD model and I'm not sure about the just released refreshed version of the Model S, which is reported to have a reduced frunk even for the RWD version.
I really don't want a heavy, loose wheel/tire in the trunk in the event of a crash and would have to come up with a way to secure it to put it in the back. I presume that Teslas in Australia have a spare tire and wonder where and how it is installed.
There is a thread on spare tires and others have found that a BMW compact spare fits the car. But I wanted a tire that I can use for hundreds of miles if necessary. I view it as insurance against a flat that I can't repair with a plug kit, so that I can continue with a long trip without having to arrange for a very long tow to a city. I gather that the vast majority of Tesla owners neither need or want a spare tire because calling for a tow in the unlikely event of a flat is easy for them. Not so for me, given where I drive.�
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