Model 3's awesome Neutral coasting / Is it more cost effective than regenerative braking?

[stretchymantis]

So I have an admittedly old, but still current, bad habit of tossing my cars into Neutral during long straights or downhills to coast and save a few mph. I do it on the Model 3 too, especially since the regenerative braking can be quite aggressive. So, two things I want to mention:

1) When coasting in Neutral, this car just does. not. stop. I've Neutral coasted every car I've owned (around ~15), and I've never had a car coast even marginally as well as Model 3. Does anyone know if there's something specific about how they managed this, short of just really awesome wheel bearings and maybe better drag?

2) Since it has regen braking, does anyone know if the amount of electricity recouped through regen is better than Neutral coasting for a ways? Sure you lose the added juice but you can travel so freaking far while coasting that it feels like the gained range more than makes up for it. Any thoughts are appreciated. I'm just curious what you all think.

Thanks.

 

[chillaban]

Changing speed is inefficient (regen 5mph, accelerate 5mph, that's not energy neural due to inefficiency in both directions). But if you control the accelerator pedal to not have any energy output on your bar, it's about equivalent to neutral coasting.

But really in reality, the range difference between neutral coasting and a slight bit of acceleration or deceleration from attempting to cruise is extremely minimal. It's definitely in the realm of hypermiling.

 

[Msjulie]

A couple years back I took a class in converting ICE to EV (I always hoped I would actually do it but.. Model 3)

Anyway, the regen vs coast question came up a lot and the instructor cited a study (sigh I do not have the source) which backed up what I always thought was true: regen's strength is when you reclaim lost energy vs using friction brakes. Otherwise coasting wins. That's the basics anyway.

I think I've gotten pretty good at managing the throttle but can our rear motors can ever freewheel? Permanent magnet and all?

It's interesting for me to note that our Audi hybrid does not do regen unless your foot is on the brake and then it's some form of blended braking. The exception is being in 'sport mode' where regen does activate on throttle lift giving you a semi-passable engine-drag experience.

When not in sport mode, you can watch the hi-tech display show you engine, battery or nothing happening based on throttle input; ie the Audi often coasts and what I read is they were going for optimal fuel economy cause they needed to get the best numbers possible. It is pretty good for an ICE car, easy upper 30s mpg even at +speed limit speeds with a full load. FWIW

 

[Mash]

So I have an admittedly old, but still current, bad habit of tossing my cars into Neutral during long straights or downhills to coast and save a few mph. I do it on the Model 3 too, especially since the regenerative braking can be quite aggressive. So, two things I want to mention:

1) When coasting in Neutral, this car just does. not. stop. I've Neutral coasted every car I've owned (around ~15), and I've never had a car coast even marginally as well as Model 3. Does anyone know if there's something specific about how they managed this, short of just really awesome wheel bearings and maybe better drag?

2) Since it has regen braking, does anyone know if the amount of electricity recouped through regen is better than Neutral coasting for a ways? Sure you lose the added juice but you can travel so freaking far while coasting that it feels like the gained range more than makes up for it. Any thoughts are appreciated. I'm just curious what you all think.

Thanks.

Model 3 is very heavy for the size of it. You don't realize that since center of gravity is very low. But that is primary reason it coasts so well. Next thing is lowest production sedan drag, low friction wheel bearings and quite narrow tires for the weight.

And coasting by definition keeps kinetic energy better than multiple steps of energy conversion. But if you're keeping on cruise - it goes to neutral by itself. You're not saving energy at all by going neutral.

Speaking of which, I wish they were able to make a mode where it engages regen only when you press brakes and goes to hydraulics once regen limit is used. But that would require expensive brake system to work good, so cost savings.

I also hope that's what they will do on Roadster. Because with proper electric brakes you can do very predictable linear curve of braking that is unachievable in hydraulic brake system. You can have tunable brake curve to your taste to emulate practically any brake system, you can give tunable force feedback...

Ideally with improved batteries and motors you don't need any mechanical brakes. Just need supercapacitors buffer to get roughly 10MW of power for a short period of time to get perfect brakes and complete regen.

 

[dsgerbc]

But that is primary reason it coasts so well.

Uhm, how exactly would the weight help a car coast? The weight doesn't matter to a first approximation.

It's the rolling resitance/drag. It only makes sense, cause the whole concept of a long range EV depends critically on those being low.

Also, coasting in either ICE/EV is pretty dangerous, cause it requires extra non-instinctive action in an emergency. There's zero reason to do it regardless of propulsion.

 

[Mash]

Uhm, how exactly would the weight help a car coast? The weight doesn't matter to a first approximation.

It's the rolling resitance/drag. It only makes sense, cause the whole concept of a long range EV depends critically on those being low.

Also, coasting in either ICE/EV is pretty dangerous, cause it requires extra non-instinctive action in an emergency. There's zero reason to do it regardless of propulsion.

Weight defines your kinetic energy at speed. You lose that energy by heating up things. Like air, road, tires, motor, transmission and suspension parts mostly through friction. More weight - lower speed loss with other things equal.

For sure, lower drag, lower transmission loss - those help significantly as well.

 

[dsgerbc]

Weight defines your kinetic energy at speed. You lose that energy by heating up things. Like air, road, tires, motor, transmission and suspension parts mostly through friction. More weight - lower speed loss with other things equal.

Two largest forces working to slow an EV are drag and tire rolling friction.

The latter is generally proportional to mass/load (for the same tire model appropriately chosen for the car), so, the rate of deceleration won't depend on vehicle's mass to a first approximation.

Tire model still matters though, and EVs tend to have low friction models.

Air resistance is proportional to the frontal area, which does not depend on mass right away, but the 3 being a normal-proportioned car, the frontal area likely scales with mass as well.

Basically, it's just tires and low drag. Weight/mass is not a factor.

 

[Mash]

What? Weight is not a factor? Tires rolling resistance is much smaller than drag, that completely independent of weight. Certainly if you going to decrease same car weight it will decelerate faster proportionally to weight loss. Main factors vs other cars are weight, drag and transmission loss difference. In that order.

 

[dsgerbc]

What? Weight is not a factor? Tires rolling resistance is much smaller than drag, that completely independent of weight. Certainly if you going to decrease same car weight it will decelerate faster proportionally to weight loss. Main factors vs other cars are weight, drag and transmission loss difference. In that order.

Tire resistance is small potatoes at higher speeds. RWD 3 weighs like a normal car of similar size (3600ish lbs). The only thing that's very different is the drag coefficient.

 

[Performance]

Weight defines your kinetic energy at speed.
More weight - lower speed loss with other things equal.

This is correct.
Physics.

 

[Dolemite]

I was amazed the first time I put it into neutral, too - almost felt like the car was accelerating.

4,000+ lbs car + narrow plastic tires + low drag + minimizing mechanical friction = crazy neutral coasting.

 

[dsgerbc]

This is correct.
Physics.

Like I said, RWD 3 weight is very similar to most other sedans. So, no, it's not weight. At highway speeds, it's the drag that's 20-30 lower than most regular sedans.

 

[destructure00]

Can't you effectively put the car in neutral, without putting it in neutral, by managing the accelerator pedal and keeping the green/black bar right in the middle? It's not like there's a physical gear shift happening to disconnect the wheels from the engine, like on ICE, when the car goes to neutral.

 

[Performance]

Like I said, RWD 3 weight is very similar to most other sedans. So, no, it's not weight. At highway speeds, it's the drag that's 20-30 lower than most regular sedans.

You asked how weight would help a car coast. He gave you a correct answer.

I'm pretty sure it is the first thing you learn on day one of freshman high school physics class.
Inertia, mass, newton....

No one is trying to tell you that the model 3 isn't aero.

 

[dsgerbc]

You asked how weight would help a car coast. He gave you a correct answer.

I'm pretty sure it is the first thing you learn on day one of freshman high school physics class.
Inertia, mass, newton....

No one is trying to tell you that the model 3 isn't aero.

Frontal area is not a fixed design parameter, is scales up with the size of the car. Larger car typically means higher weight.

Inertial is proportional to weight, air resistance scales with car size/weight. Deceleration won't depend on weight much.

A semi truck won't coast well despite its weight.

 

[vogz]

Model 3 is very heavy for the size of it.

Agree with the rest of your post so I’ll only quote this part that I disagree with. The Model 3 is not a small car, and it’s size to weight ratio is actually very similar to other mid size luxury sedans that have AWD (using the dual motor versions for this comparison, but it also holds true for the SR+ model). It has virtually the same dimensions as my previous car (2011 Audi S4). Both cars are luxury sport sedans with AWD. Both have curb weights right around 4000lbs. Same with the current MB C43AMG and the BMW M340i x-drive. All right around 4000lbs and similar exterior dimensions.

 

[Uncle Paul]

Model 3 has great Aero.

 

[Msjulie]

Can't you effectively put the car in neutral, without putting it in neutral, by managing the accelerator pedal and keeping the green/black bar right in the middle?

I've watched my car via Scan My Tesla when there's no visible green or black bar and it gets close to being zero, need to try more to really know. It sure does not feel like our Audi does when it's coasting. To be fair I have not tried neutral outside a (no touch!) car wash

 

[XLR82XS]

Can't you effectively put the car in neutral, without putting it in neutral, by managing the accelerator pedal and keeping the green/black bar right in the middle? It's not like there's a physical gear shift happening to disconnect the wheels from the engine, like on ICE, when the car goes to neutral.

Yes. I would never use neutral to coast. In an emergency it could be a problem.

 

[qingshan]

Frontal area is not a fixed design parameter, is scales up with the size of the car. Larger car typically means higher weight.

A semi truck won't coast well despite its weight.

Physics and welding I never took. Semi escape ramps speak to how hard it is to slow semi trucks. My thought was that since weight/mass is related to inertia and that inertia might just relate to regen...