Tesla removes regenerative braking strength option

[ZOMGVTEK]

I find it’s easier to control the vehicle on slick conditions with low regen. The trouble is, if you need to lift your foot to apply friction brakes, the regen will come on stronger than the tires are capable of tolerating, break loose, and the vehicle is unsettled. If this happens around a corner, it’s a bit sketchy at times, especially if it’s a concrete highway off ramp on carbide studded tires. Personally I still do use normal regen, but removing the option for low isn’t stellar in my view. Having low gives me a bit more confidence handing the vehicle off to someone else in poor weather. The car is basically RWD until slip is detected, and it regens with the rear motor until the car slides. It usually corrects with under 10 degrees of yaw, but it can be 30 or so in poor conditions at moderate speed. It’s rather sketchy if you’re not expecting it, and gives a good reason to drive with both feet if you’re cornering aggressively in a tight area. I guess you can just drive slow, but that’s no fun.

Hopefully they continue to improve the vehicles response in very poor weather. It has what I consider to be a very considerable room for improvement. The behavior at times is really quite awful, and among the worst offenders in the industry in some conditions. It’s stellar in a straight line, but that’s about it. It’s strange since it’s great as long as there’s a little traction, but once it gets to be really bad, the car turns into a train wreck and the systems barely work.

 

[derotam]

Physics eh? My physics teachers taught me science was proven with experimentation, not discussion. I think your logic is flawed because the real world is not an empty pinewood derby ramp. You go ahead and prove your physics with a go-pro going up and down centreville road on low regen. I'll match your path on standard and we can compare who went a further with 10% battery.

Sure, break out your Scan My Tesla App with an OBDII adapter hooked into your car and we can see the energy levels after going from lets say Frying Pan Road to McLearen. You drive with Standard regen, and regen down the hill to maintain the speed limit and then use power to go back up the hill to Mclearen, and I will use it doesn't matter standard or low cause I will just coast down the hill and then coast back up the hill.

This doesn't even take experimentation because there is math. Lets simplify the game now. An object gains x amount of energy dropping a certain distance based on mass, air resistance, and gravity. The same object requires x amount of energy to be raised a certain distance. There is a LOSS when you regen, you do not get a 100% recapture of energy. It is about 90% efficient.

 

[derotam]

The only thing that matters here is EPA rating. It is not about optimal coasting which you can technically do, but rather specific tests performed during EPA certification. Put it another way, Regen=Standard will likely give higher EPA rating than Regen=Low. Just because of some energy will go back to the battery rather than to heat via friction brakes.

Depends on how the test is conducted. It is a standardized test. I also think that regen is disabled for the current standardized test. someone could correct me if I am wrong but I thought that is what I read in the original Model 3 EPA test documentation.

 

[derotam]

This kind of thing is why IMO while "coasting" is better in a perfect world, in teh real world it his limited practical benefits over running max regen. every hill within 100 miles of me is too steep to fully coast, you'll have to limit your speed at some point or you're breaking the law, and setting the cruise control allows the car to manage the right amount of regen vs set speed for you.

Around town there is enough stop and go + unpredictable people around you that the "perfect coast" isn't worth pursuing constantly IMO. Though if you wanted to, its possible to adjust the accelerator enough to be very either very slightly regen'ing or very slightly accelerating, which would be the closest to "coasting" .. however the accelerator is almost too sensitive for this (also you'd have to stare at the regen/accel bar on the screen to get it about right) and for me it seems like I would spend too much time "trying to coast" for very little benefit over just slowing down with regen when I need to.

Yes it is all a game. I mean if we want to just say you have to maintain the EXACT speed limit ALL the time, then yes there would be no coasting except for slowing down because of an upcoming stop or slowdown in traffic. Technically you are breaking the law going 1 MPH over right, but you would rarely get a ticket for that. Commonly people go 5-10 MPH over the limit. Everyone drives differentyl and everyone has their own mindset as to what is practical or not. You have hypermilers that do all kinds of things. Personally, in a hilly drive, at the top of a hill I may coast off 5mph before the downhill and then coast to +5 to 10 over limit on the downhill, then coast back to limit. Before covid, on my normal commute I found doing this saved me an average of around 30Wh/mile. And that was not with big hills at all.

Again, it's all a game and how you play. Some people think it is too much work, sometimes it isn't worth it for all kinds of reasons.

 

[TIppy]

Sure, break out your Scan My Tesla App with an OBDII adapter hooked into your car and we can see the energy levels after going from lets say Frying Pan Road to McLearen. You drive with Standard regen, and regen down the hill to maintain the speed limit and then use power to go back up the hill to Mclearen, and I will use it doesn't matter standard or low cause I will just coast down the hill and then coast back up the hill.

This doesn't even take experimentation because there is math. Lets simplify the game now. An object gains x amount of energy dropping a certain distance based on mass, air resistance, and gravity. The same object requires x amount of energy to be raised a certain distance. There is a LOSS when you regen, you do not get a 100% recapture of energy. It is about 90% efficient.

You are not taking dissipative terms into account. The amount of power it takes to move the care goes up non-linearly with speed, ultimately as speed cubed. So coasting at high speeds is bleeding off energy much faster than at low speeds. If you cover the same distance in the same amount of time by coasting or driving under power at a constant speed, the average speed will be the same. But while coasting you will be, at times, traveling at speeds higher than average and dissipating considerably more energy per unit time. If you are traveling at highway speeds and regen quickly down to the average speed, you will capture some of the kinetic energy in the battery. You can then use this energy to drive at the average speed where the dissipative forces are much lower. There will be a break even point depending on the round trip regen efficiency.

When I used the efficiency data that Tesla released for the roadster years ago, it turned out that it was more efficient to regen down to the average speed and drive at that speed to cover the same distance.

 

[derotam]

You are not taking dissipative terms into account. The amount of power it takes to move the care goes up non-linearly with speed, ultimately as speed cubed. So coasting at high speeds is bleeding off energy much faster than at low speeds. If you cover the same distance in the same amount of time by coasting or driving under power at a constant speed, the average speed will be the same. But while coasting you will be, at times, traveling at speeds higher than average and dissipating considerably more energy per unit time. If you are traveling at highway speeds and regen quickly down to the average speed, you will capture some of the kinetic energy in the battery. You can then use this energy to drive at the average speed where the dissipative forces are much lower. There will be a break even point depending on the round trip regen efficiency.

When I used the efficiency data that Tesla released for the roadster years ago, it turned out that it was more efficient to regen down to the average speed and drive at that speed to cover the same distance.

I never said anything about ensuring two people travel the same distance in the same TIME period. I also agree that speed will play a factor because of air resistance, but the bottom line is regen is probably only 90% efficient. If you take a downhill/uphill combination and either test it or do the math, with regen only being 90% efficient, coasting will always beat regen in terms of net energy expended to go x distance, with time not being a factor. Whether the gain is significant enough for someone to do it or not doesn't have anything to do with the mathematical result.

 

[TIppy]

I never said anything about ensuring two people travel the same distance in the same TIME period. I also agree that speed will play a factor because of air resistance, but the bottom line is regen is probably only 90% efficient. If you take a downhill/uphill combination and either test it or do the math, with regen only being 90% efficient, coasting will always beat regen in terms of net energy expended to go x distance, with time not being a factor. Whether the gain is significant enough for someone to do it or not doesn't have anything to do with the mathematical result.

If you coast down a hill and let your speed go uncontrolled you will be burning through your potential energy much faster. Coasting is not free, you use more or less of your potential energy to get to the bottom of the hill, depending on speed.

 

[derotam]

If you coast down a hill and let your speed go uncontrolled you will be burning through your potential energy much faster. Coasting is not free, you use more or less of your potential energy to get to the bottom of the hill, depending on speed.

If I coast down a hill I gain 100% of the gravity induced gains minus any resistive factors(rolling resistance, air resistance, etc). If I regen down the hill I capture the gravity induced energy minus the same resistive factors and ALSO minus the regen energy conversion efficiency loss. With coasting, until the resistive forces negate the gravity gains, I win. When the resistive forces equal the gravity gains, its a wash.

 

[TIppy]

If I coast down a hill I gain 100% of the gravity induced gains minus any resistive factors(rolling resistance, air resistance, etc). If I regen down the hill I capture the gravity induced energy minus the same resistive factors and ALSO minus the regen energy conversion efficiency loss. With coasting, until the resistive forces negate the gravity gains, I win. When the resistive forces equal the gravity gains, its a wash.

If you regen, you can keep your speed lower, so you would dissipate considerably less energy to the environment. That energy would go into the battery instead. It always take more energy to cover the same distance in less time, ie at a higher speed.

 

[derotam]

If you regen, you can keep your speed lower, so you would dissipate considerably less energy to the environment. That energy would go into the battery instead. It always take more energy to cover the same distance in less time, ie at a higher speed.

So you tell me, what energy is being dissipated into the environment when coasting?

 

[TIppy]

So you tell me, what energy is being dissipated into the environment when coasting?

Yes. That's what the dissipative forces are doing. They're heating the air, the oil in the transmission, the tires, etc.

 

[derotam]

Yes. That's what the dissipative forces are doing. They're heating the air, the oil in the transmission, the tires, etc.

Are you trying to say that if I coast lets say 10mph faster that the increased "heating of the air"...due to speed is going to negate the 10% efficiency loss of regen?

 

[TIppy]

Are you trying to say that if I coast lets say 10mph faster that the increased "heating of the air"...due to speed is going to negate the 10% efficiency loss of regen?

Let's say the difference is 90 mph vs 80 mph. The ratio of those speeds is 1.125. At those speeds aerodynamic drag prevails, so the amount of energy to cover the same distance goes up as the speed squared. That's 1.125 * 1.125, or 1.27. That's 27 percent more energy.

 

[LionXng]

Sure, break out your Scan My Tesla App with an OBDII adapter hooked into your car and we can see the energy levels after going from lets say Frying Pan Road to McLearen. You drive with Standard regen, and regen down the hill to maintain the speed limit and then use power to go back up the hill to Mclearen, and I will use it doesn't matter standard or low cause I will just coast down the hill and then coast back up the hill.

This doesn't even take experimentation because there is math. Lets simplify the game now. An object gains x amount of energy dropping a certain distance based on mass, air resistance, and gravity. The same object requires x amount of energy to be raised a certain distance. There is a LOSS when you regen, you do not get a 100% recapture of energy. It is about 90% efficient.

You are not considering all variables because, again, the real world is not your mythical pinewood derby track. There are a lot more factors in the real world than your thought experiment on regen efficiency. The scientific method requires experimentation. Prove your theory with real driving while recording the numbers. Otherwise you are just blowing hot air.

 

[derotam]

Let's say the difference is 90 mph vs 80 mph. The ratio of those speeds is 1.125. At those speeds aerodynamic drag prevails, so the amount of energy to cover the same distance goes up as the speed squared. That's 1.125 * 1.125, or 1.27. That's 27 percent more energy.

Absolutely, but if the force of gravity is still speeding up my vehicle at 90mph going down a hill, then I am still adding more kinetic energy to the vehicle then regen is adding to the battery because it is still only 90% efficient. Again, until drag forces MATCH the gravity force on a given decline, I still win.

 

[derotam]

You are not considering all variables because, again, the real world is not your mythical pinewood derby track. There are a lot more factors in the real world than your thought experiment on regen efficiency. The scientific method requires experimentation. Prove your theory with real driving while recording the numbers. Otherwise you are just blowing hot air.

And going 90mph in a state where the max is 55 is not exactly real world usage either...but I still win as long as gravity overcomes all drag forces.

 

[holmgang]

if you never have to brake going down a slope, so all the energy gained goes back into pushing the car up the slope, coasting wins.

if you ever have to brake going down a slope (to slow for corners; because theres a stop at the bottom; etc), regen wins. because the joules that goes out through the calipers, are going back into the battery instead, even if a fraction of it

 

[derotam]

if you never have to brake going down a slope, so all the energy gained goes back into pushing the car up the slope, coasting wins.

if you ever have to brake going down a slope (to slow for corners; because theres a stop at the bottom; etc), regen wins. because the joules that goes out through the calipers, are going back into the battery instead, even if a fraction of it

Exactly.

 

[TimothyHW3]

This is really bad if true. I had a situation where the standard feature was terrible on a 100% snowy hill going down. The car was basically undrivable, because it slid even with smallest lifting of the break pedal. Once I turned the low on it was far better.

 

[TIppy]

Absolutely, but if the force of gravity is still speeding up my vehicle at 90mph going down a hill, then I am still adding more kinetic energy to the vehicle then regen is adding to the battery because it is still only 90% efficient. Again, until drag forces MATCH the gravity force on a given decline, I still win.

If the slope of the hill is still speeding you up, you'll soon be dissipating ever higher excess energy to the environment. You have a certain amount of potential energy at the top of the hill. Every bit of your initial potential energy that you lose to the environment is not there to get you up the other side of the hill. Why do you think the heat you generate in the air is different than the heat generated as losses in regen to the battery?

We're talking about the laws of physics here, not of your local jurisdiction. You made an unqualified statement that coasting was always more efficient than regen, but clearly it isn't.

At lower speeds, 10 mph will be a higher ratio of the two speeds, but the energy required for a given distance will be less than a squared relationship to speed, but still greater than linear.