Stop the Press! Tesla announces REAL HP numbers for P85D and P90L

[chickensevil]

I mean there is no way currently (that we know of) to get 691HP from the pack even if using the new 90kWh. So it seems to me that the choices were, we are sorry but you can have the upgrade at a discount, or here have your money back (there may be strings attached to this.) Most people are not going to want to give up their cars, so it will be the upgrade or nothing for them most likely at this point. I'm a bit surprised to see them buy back the car, but if it prevents some long drawn out legal action it is likely the better of choices.

 

[stopcrazypp]

vgrinshpun - as I understand you and others, you advocate that the 691 hp motorpower was the most correct way to advertise the power of the P85D, since that was the best way to tell the customers about the acceleration, torque etc. Because telling those things with 0-60 times and actual torque numbers would not reflect real life performance.
...

I don't think vgrinshpun is saying that. He is saying that only the battery-limited power number (without the motor power number) combined with those numbers, as some are advocating, does not tell the whole story. He does not advocate using only the motor power number alone (he has said previously the current situation with both numbers is better). It is a counterpoint against those that continue to push the idea that the motor power number was complete nonsense and worthless.

 

[stopcrazypp]

I know the 0-60 performance is similar - that's the whole point, the individual numbers can vary significantly relative to each other (in this case acceleration and HP similar but torque very different) so justification based on ratios is flawed. Lets consider if Tesla changed their gearing for instance which sacrificed 0-60 but gave much better high speed performance. Battery limits stayed the same. Torque stayed the same. Motor power stayed the same. Everything stayed the same, just a change in gearing. We end up with a car that has a 0-60 time the same as those BMWs but much better mid range performance. The need to equate the car to a 691hp car would now seem irrelevant.

I have seen similar talk about gear ratios for better high speed performance, but that seems to show a fundamental misunderstanding of the electric motors. Even if Tesla changed their gearing to higher, all that will result in is higher top speed (assuming the power output is enough for the aerodynamic load). It will not help high speed acceleration at all. This is because a gearing change not only extends the torque curve wider, but also proportionally lowers the wheel torque.

I did a quick graph using sorka's P85 to illustrate the point. I picked P85 because it doesn't have the complexity of battery limits or dual motors. The purple parts are the original, the red part illustrates what would happened if selecting a 1.25x (numerically 0.8x) gear ratio (basically instead of 9.73 it is 7.78). You will see that the wheel torque doesn't improve at all (except for a very tiny bit of noisy areas), so acceleration throughout the rev range does not improve, but the lower end suffers. The only way to improve is by changing the motors itself (which is where motor power comes in).

 

[kennybobby]

Sacha's crappy dyno data

Wow he really got taken for a ride-- that is an ugly chart to use as the basis for a hp claim, but i guess it worked for his purposes of getting a buy-back.

The traction control was causing oscillation in the low-speed data (probably different front and rear wheel speeds) to the point of making it impossible to get a decent reading--i'd want a refund from the dyno man too...lol

 

[lolachampcar]

You just gota love that low end torque!
It's almost evil.

 

[MuppetOwl]

Latest news from Germany and the EU regulation is that summation of motor hp like Tesla have done is not allowed.

According to the EU regulation, the summation is not allowed. For good reason, because the battery both electric motors is not able simultaneously to operate at full load. Therefore Tesla must indicate a maximum achievable maximum power, taking into account this circumstance.

Im Autoquartett abgehängt: Tesla verliert ordentlich PS - n-tv.de

 

[stopcrazypp]

i think your chart is off. A 12:1 gearbox would result in higher torque at the wheels, not less.

Right, corrected. Chart was correct, number was wrong in my haste to make a quick late night post, it should be 7.78 (1/1.25x or 0.8x).

- - - Updated - - -

Latest news from Germany and the EU regulation is that summation of motor hp like Tesla have done is not allowed.

Im Autoquartett abgehängt: Tesla verliert ordentlich PS - n-tv.de

That is the interpretation of the author on the changes made to the website in posting the "battery-limited" numbers. It does not say there is any regulatory body that made that decision. Someone previously queried the organization on the addition of the two motors and the response was that part was open to interpretation to be determined by the member parties (the regulation itself does not mention how to handle dual motors). As I put before, direct summation would only be wrong if the gearing differences of the two motors make it so it doesn't hit the max power at the same time.

At any rate, even the current single motors number do not match the theory of battery being factored in as regulatory required. The battery limited number is 463 hp which is still lower than the single 503 hp motor power of the rear motor.

I only have the Google translate to go by, but it seems the author also interpreted the recent seatbelt recall incorrectly and also Consumer Reports' pulling of their recommendation.

 

[legislator]

stopcrazypp:

If you want higher acceleration you don't want higher gearing, but lower.

I don't think it's a misunderstanding about electric motors, gearing is a concept that works with every kind of motor.

For maximum acceleration you want to use the lowest possible gear until the torque breaths out, for every gear available. The highest gear is almost always purely for top speed and not acceleration.

 

[Auzie]

stopcrazypp:

If you want higher acceleration you don't want higher gearing, but lower.

I don't think it's a misunderstanding about electric motors, gearing is a concept that works with every kind of motor.

For maximum acceleration you want to use the lowest possible gear until the torque breaths out, for every gear available. The highest gear is almost always purely for top speed and not acceleration.

I think scp is saying the same as you, just with words organized in a different way

.......................................
Even if Tesla changed their gearing to higher, all that will result in is higher top speed (assuming the power output is enough for the aerodynamic load). It will not help high speed acceleration at all. This is because a gearing change not only extends the torque curve wider, but also proportionally lowers the wheel torque.
..............................

 

[AWDtsla]

stopcrazypp:

If you want higher acceleration you don't want higher gearing, but lower.

I don't think it's a misunderstanding about electric motors, gearing is a concept that works with every kind of motor.

For maximum acceleration you want to use the lowest possible gear until the torque breaths out, for every gear available. The highest gear is almost always purely for top speed and not acceleration.

Multiple gears in a transmission are for overcoming inherent weaknesses of piston engines, they have no torque at low rpms and have relatively low speed limits.

 

[stopcrazypp]

stopcrazypp:

If you want higher acceleration you don't want higher gearing, but lower.

I don't think it's a misunderstanding about electric motors, gearing is a concept that works with every kind of motor.

For maximum acceleration you want to use the lowest possible gear until the torque breaths out, for every gear available. The highest gear is almost always purely for top speed and not acceleration.

Like Auzie said, I'm saying the same thing as you are. I just worded it different. The person I responded to (JonG) suggested that switching to gearing that sacrificed 0-60 would yield better higher end acceleration. The only way to do that is with higher gear (which might work with an ICE torque curve, but not in this case though). If I picked a lower gear that will improve the 0-60, not "sacrifice" it (it'll also lower the top speed).

 

[JonG]

Like Auzie said, I'm saying the same thing as you are. I just worded it different. The person I responded to (JonG) suggested that switching to gearing that sacrificed 0-60 would yield better higher end acceleration. The only way to do that is with higher gear (which might work with an ICE torque curve, but not in this case though). If I picked a lower gear that will improve the 0-60, not "sacrifice" it (it'll also lower the top speed).

and I've been thinking about what you said and can see that now in the case of EVs. thx.

 

[chickensevil]

Maybe I am misunderstanding how gearing works. But I thought for an ICE it allowed a "reset" of the gears such that you could target the optimum power to gear ratio. In this case peak power happens between like 15-40MPH and then drops off. So if you can take that RPM value and target it in a higher gear shouldn't it slide the power band to the right such that you won't get as much power in gear two but it will stay in the power band for a wider range.

In an ICE peak power tends to be at like 4-5k RPMs (for example) and therefore the different gears allow for retargeting of that peak power at different speeds. Otherwise how do you go from amazing acceleration in first speed from like 0-40, and then shift to second and get decent acceleration from 40-80, then shift again and get OK acceleration from 80-100 and so on. Is this something that only favors ICE because the power is back loaded (eg when the RPMs are in the 5k-6k range or whatever) vice the EV motor which is front loaded power so you never get to move that sweet spot?

 

[vgrinshpun]

"What I understand and I think you are missing is that P85+ rear motor has torque rating of 443lb-ft and weighs about 300lbs less than P85D that has 55% more torque - 686lb-ft. This 55% jump in torque is what is responsible for the most of the improvement in 0 to 60 mph acceleration, NOT the 417hp to 463hp rating of the battery. I am really surprised that this need to be discussed with a person with racing experience like yourself."

Ok, I am slightly less irritated with you now as you really do not understand. I really thought you were being argumentative and out to yank my chain.

I specifically avoided quoting exact numbers as you have a tendancy to jump over posters that do not use exact figures. Using yours should be safe.

Put your 443 ft-lb P+ next to a 686 ft-lb P+ (call it a P++). Light the fuse and let it burn to the battery limit (same for both the P+ and P++ in this instance). I think you can see that there will be little performance difference between the two. The P++ may be a smidgen quicker depending upon the portion of the run that is beyond traction limited but not yet to battery limited.

Put your 443 ft-lb P+ next to a 686 ft-lb P+. Light the fuse and let it burn to the battery limit for the P+ on the stock P+ version of the battery and to the P85D battery limit on the P++. The added battery limit will improve the P++'s performance past the point of the P+ being battery limited. The P++ will be slightly quicker than the version of this test above.

Now line up a P+ and a P85D. Light the fuse and you will find the P85D is WAY quicker than the P+.

This tells me that Motor Torque has a little positive effect. More battery power has even more effect. Lastly, hold your breath for this one, all wheel drive has the most impact on quickness.

So I stand by my question. I give Tesla engineers a tremendous amount of credit for the engineering they have done. With that credit comes the knowledge that they know exactly how the car performs along with knowing the above three scenarios are accurate. So why would bright capable engineers (actually, just one in this case as the whole show is run by one guy) choose to describe their product using the least descriptive power related variable?


Also, given your proclivity for numbers, can you put together the battery limited power, combined motor power and available torque for the S85D and stack that up against the P+ for us? I suspect the results will be interesting

- - - Updated - - -

Returning to gears and gearboxes is enjoyable. A mass accelerates as a function of the energy you are imparting to it (from the battery). Unless you have a significant issue with efficiency (or back EMF), you only get out of the car what the battery is putting into it. Gears will help with back emf but they will do nothing for sucking more power out of the battery.

I’ve put together few charts that illustrate the point that I’ve been making for some time: that the improvement in 0-60mph acceleration that Tesla was able to achieve in P85D vs P85/85D (0.8 sec), in spite of the power limitation imposed by the battery, is mostly due to the increased combined torque available from the two motors with more that 50% increased power rating (686lb-ft in P85D vs. 443 lb-ft in P85).

First, few basics. As I mentioned before, based on the Second Newtown Law, acceleration is defined by the applied force. As applied to the rotational motion, the acceleration *time* is defined by the applied torque and is proportional to total connected inertia and reciprocal to the accelerating torque (the difference between the torque of the motor and the load torque). For those interested in more details, they are available from the “Calculating Motor Start Time” on-line course. The pertinent formula illustrating the above statement is included below.

The acceleration time can be calculated using the following formula:
t[SUB]a[/SUB] = Wk[SUP]2[/SUP] * Delta N / 308 * Ta
Where t[SUB]a[/SUB] acceleration time (seconds);
Wk2 total connected inertia (lb * ft2 );
Delta N speed change during time ta (rev/min);
Ta average accelerating torque (lb * ft) (average motor torque – average load torque);

As I’ve mentioned many times before, based on the above, the accurate estimate of acceleration can be performed only by analyzing the torque and power curves, not by comparing a single point from these curves across technologically different drivetrains which yield very different torque and power curves.

Here is how the idea of acceleration being accurately ascertained using the torque curve was expressed by the former Mazda Engineer that worked on Miata Project in his book (Norman H.Garrett III, Mazda Miata Performance Handbook):

So, I started with building the power curves for the P85 and P85D, based on description that I’ve provided here. The curves are based on current specification of the P85D (728hp), because I did not have access to the rpm values that correspond to the older (691hp) specification. The curves are idealized, i.e. do not take into account transients and decrease in power output of the motors at higher speeds, as I do not have the necessary data to accurately represent these effects.

The combined power curves for P85 and P85D are shown using shading – the green area outlines P85 curve, while green plus yellow area outline the P85D power curve. There are two charts – one using rpm on the horizontal axis, another – mph. The mph are calculated based on 9.73:1 ratio (common for both front and rear motors per the Model S Manual) and based on the tirerack data for the 245/35R21 Continental DW summer tires (750 revolutions per mile).

The torque curves are built based on the power curves, taking into account that the drivetrain outputs rated torque (horizontal portion of the torque curve) up to the speed at which it reaches its power limit. After this inflection point the torque declines with the increase of rotational speed (rpm) so that power limit is not exceeded. The torque curves are built neglecting the transients and the fact that the power limitation imposed by the battery is not a horizontal line, but a line that is sloping down with the increase in rpm.

As seen from the attached charts, the increase of the area under the torque curves from 0-60mph (which is proportional to power) can be divided into three areas. Area A represents improvement in acceleration due to the increased combined torque of P85D over the P85 (686lb-ft vs.443lb-ft). Area B represents improvement due to the increase in power limit of the battery from 416hp to 463hp. Area C represents improvement in acceleration due to both motor torque and battery limit improvements.

I will do actual calculations next week, but as can be seen from the graphical presentation, splitting area C in half, with each half allocated to the improved acceleration due to torque and horsepower improvement, it is clear that (0-60mph) acceleration improvement due to the increase in combined rating of the drivetrain motors dwarfs improvement due to increased power from the battery. Just eye balling it for now, I would say that 85-90% is due to the increased drivetrain motors, while 10-15% is due to increase in battery power.

In summary, your conclusions are not consistent with the data and are simply wrong.

The analysis of these curves, as I alluded before, leads to several additional implications, including the one that I repeatedly referred to by saying that square peg does not fit into the round hole, and I am sure that the lively discussion on this topic (as it is central to the assertion made in the unhappy owner’s letter) is next…

 

[wk057]

I’ve put together few charts that illustrate the point that I’ve been making for some time: that the improvement in 0-60mph acceleration that Tesla was able to achieve in P85D vs P85/85D (0.8 sec), in spite of the power limitation imposed by the battery, is mostly due to the increased combined torque available from the two motors with more that 50% increased power rating (686lb-ft in P85D vs. 443 lb-ft in P85).

First, few basics. As I mentioned before, based on the Second Newtown Law, acceleration is defined by the applied force. As applied to the rotational motion, the acceleration *time* is defined by the applied torque and is proportional to total connected inertia and reciprocal to the accelerating torque (the difference between the torque of the motor and the load torque). For those interested in more details, they are available from the “Calculating Motor Start Time” on-line course. The pertinent formula illustrating the above statement is included below.



As I’ve mentioned many times before, based on the above, the accurate estimate of acceleration can be performed only by analyzing the torque and power curves, not by comparing a single point from these curves across technologically different drivetrains which yield very different torque and power curves.

Here is how the idea of acceleration being accurately ascertained using the torque curve was expressed by the former Mazda Engineer that worked on Miata Project in his book (Norman H.Garrett III, Mazda Miata Performance Handbook):

View attachment 102730

So, I started with building the power curves for the P85 and P85D, based on description that I’ve provided here. The curves are based on current specification of the P85D (728hp), because I did not have access to the rpm values that correspond to the older (691hp) specification. The curves are idealized, i.e. do not take into account transients and decrease in power output of the motors at higher speeds, as I do not have the necessary data to accurately represent these effects.

The combined power curves for P85 and P85D are shown using shading – the green area outlines P85 curve, while green plus yellow area outline the P85D power curve. There are two charts – one using rpm on the horizontal axis, another – mph. The mph are calculated based on 9.73:1 ratio (common for both front and rear motors per the Model S Manual) and based on the tirerack data for the 245/35R21 Continental DW summer tires (750 revolutions per mile).

View attachment 102731

View attachment 102732

The torque curves are built based on the power curves, taking into account that the drivetrain outputs rated torque (horizontal portion of the torque curve) up to the speed at which it reaches its power limit. After this inflection point the torque declines with the increase of rotational speed (rpm) so that power limit is not exceeded. The torque curves are built neglecting the transients and the fact that the power limitation imposed by the battery is not a horizontal line, but a line that is sloping down with the increase in rpm.

View attachment 102733

View attachment 102734


As seen from the attached charts, the increase of the area under the torque curves from 0-60mph (which is proportional to power) can be divided into three areas. Area A represents improvement in acceleration due to the increased combined torque of P85D over the P85 (686lb-ft vs.443lb-ft). Area B represents improvement due to the increase in power limit of the battery from 416hp to 463hp. Area C represents improvement in acceleration due to both motor torque and battery limit improvements.

I will do actual calculations next week, but as can be seen from the graphical presentation, splitting area C in half, with each half allocated to the improved acceleration due to torque and horsepower improvement, it is clear that (0-60mph) acceleration improvement due to the increase in combined rating of the drivetrain motors dwarfs improvement due to increased power from the battery. Just eye balling it for now, I would say that 85-90% is due to the increased drivetrain motors, while 10-15% is due to increase in battery power.

In summary, your conclusions are not consistent with the data and are simply wrong.

The analysis of these curves, as I alluded before, leads to several additional implications, including the one that I repeatedly referred to by saying that square peg does not fit into the round hole, and I am sure that the lively discussion on this topic (as it is central to the assertion made in the unhappy owner’s letter) is next…

While the graphs are cool and all... they have nothing to do with the advertised "motor power" numbers. Torque, yes for sure. But the peak torque numbers and "motor power" numbers have nothing to do with each other. No one is questioning the peak torque numbers. We all know the added torque is what gives the P85D its advantage during a launch. So why all of the effort to preach to the choir on that note, except to try and represent it as something its not...

You try to make it out like this is related to the 691 HP "motor power" issue, but it is not.

 

[AWDtsla]

Maybe I am misunderstanding how gearing works. But I thought for an ICE it allowed a "reset" of the gears such that you could target the optimum power to gear ratio. In this case peak power happens between like 15-40MPH and then drops off. So if you can take that RPM value and target it in a higher gear shouldn't it slide the power band to the right such that you won't get as much power in gear two but it will stay in the power band for a wider range.

In an ICE peak power tends to be at like 4-5k RPMs (for example) and therefore the different gears allow for retargeting of that peak power at different speeds. Otherwise how do you go from amazing acceleration in first speed from like 0-40, and then shift to second and get decent acceleration from 40-80, then shift again and get OK acceleration from 80-100 and so on. Is this something that only favors ICE because the power is back loaded (eg when the RPMs are in the 5k-6k range or whatever) vice the EV motor which is front loaded power so you never get to move that sweet spot?

An ideal electric motor can output 100% power at any RPM, and therefore any speed in an electric vehicle. The relationship between torque and power is fixed by RPM. Acceleration force is just torque that has been linearized. The motors in Model S are a close enough approximation to an ideal motor, but there are realistic limitations of maximum RPM, time under power, and back-emf losses at high RPM. Even with this, the torque "curve" is very predictable - initial torque output is clipped to a maximum then power falls off with back-emf, and torque multiply so because of the fixed relationship to power.

An ICE has a terrible torque curve that requires all that junk between it and the wheels in order to make engine power output useful. This means you cannot achieve peak power at any random speed, it depends on which speed, and which gear. An ideal transmission would be a CVT, which holds maximum power and allows gradual increase of wheel RPM (therefore mathematically inversed decrease in torque). But they suck.

 

[JonG]

My take is that an ice car has a torque and power peak much further up the Rev range. Gearing simply matches that peak to the car speed.

 

[Nigel Tufnel]

Andy: Hey, stop using logical thinking to make us look stupid. Do you want to get banned again?

 

[Andyw2100]

Andy: Hey, stop using logical thinking to make us look stupid. Do you want to get banned again?

Are you confusing me with someone else? I hadn't posted in this thread for several days before this post, and I've never been banned.

 

[vgrinshpun]

While the graphs are cool and all... they have nothing to do with the advertised "motor power" numbers. Torque, yes for sure. But the peak torque numbers and "motor power" numbers have nothing to do with each other. No one is questioning the peak torque numbers. We all know the added torque is what gives the P85D its advantage during a launch. So why all of the effort to preach to the choir on that note, except to try and represent it as something its not...

You try to make it out like this is related to the 691 HP "motor power" issue, but it is not.

I've explained relationship between the motor power and torque ratings more than once. It would be interesting to read why do you think they "have nothing to do with each other".