Letter To Elon Musk Regarding P85D Horsepower – Discussion Thread

[stopcrazypp]

Can either of those two cars actually generate that combined hp number?

I had same question. In those cases it's a combination of ICE + motor, so it's mainly up to gearing. There is unlikely to be a bottleneck at the battery (battery only has to power motor while the ICE makes most of the power), which is different from the P85D.

I think the Fisker Karma is a closer analogy. It had two 150kW motors and it was advertised at 300kW / 402hp (without specifying "motor power" as Tesla did), but the generator+battery output does not make enough power for that (Fisker reduced power from generator for noise reasons).

 

[smac]

So, just curious for the folks signing the letter....

It would appear to be industry practice to present total horsepower as the sum on the motors/engines in the drivetrain: the BMW says the i8 is 357hp (129hp + 228hp) and Ferrari says the LaFerrari is 963 cv (800cv + 163 cv). So, if Tesla provides documentation of the horsepower of the two motors on the original P85D (470hp on the rear and 221hp on the front), will they be satisfied that Tesla delivered the 691hp car per the published spec?

Who cares what others do, I thought Tesla wanted to be different?

The old guard USED to publish wildly optimistic 0-60 times that only racing drivers could hit. They learnt their lesson and now pretty much every launch control car will hit the published numbers (often beating them as the manufacturers build in tolerance, as did Tesla with the P85).

In many ways I signed the letter because I've lost trust in Tesla to not be like other manufacturers.

 

[stopcrazypp]

I'm looking up more examples. It seems the SLS e-cell / electric drive is an even better example. Mercedes advertises it everywhere at 740 hp (552kW), and from one of their PR pieces, you find out it is derived from 138kW out of each motor multiplied by 4 (it has 4 motors) for 552kW total.
http://www.daimler.com/dcmedia/0-921-1739804-1-1574373-1-0-1-0-0-1-0-1549054-0-1-0-0-0-0-0.html

Curb weight of the car is 4600 lbs. No dyno results, but 0-60 is 3.6-3.8 seconds depending on which estimate you use. I have a hard time finding other performance/acceleration results from tests, but it'll be very telling to compare to the P85D.

 

[brianman]

Perhaps it's worthy of a separate thread, but I think it's probably time for TMC to have this question addressed in one of the permanent wikis:

If you feel that Tesla's public product documentation is incorrect or misleading, what is the recommended course of action for getting the issue addressed if Tesla doesn't respond to your inquiry using the recommended email channels?

I see some agreeing with Andy's approach and some disagreeing. For those disagreeing, I think it's worth spending TMC's collective intellects and skillsets to design a recommendation for future situations. Tesla has made me very confident in the last 3 years that this won't be the last occurrence of something like this.

If you truly believe in the company or the mission, trying to quietly ignore the issue is not a viable option.

To be clear, I'm talking about existing products for which money has exchanged hands. Reservation deposits is something entirely different.

 

[Auzie]

From what I see, Tesla seems to be very different to other car manufacturers, but I can't say the same for its customers.

Tesla's customers pool gets bigger and more diverse, hence more difficult to deal with.

 

[omarsultan]

Can either of those two cars actually generate that combined hp number?

I am not sure I understand the question-horsepower is typically measured at the shaft. The point was that car companies seem to derive the system power by testing the individual elements and summing the outputs.

 

[stopcrazypp]

I am not sure I understand the question-horsepower is typically measured at the shaft. The point was that car companies seem to derive the system power by testing the individual elements and summing the outputs.

His question is if the combined output at the shafts equal to that number. For example, if you dynoed at the wheels and accounted for losses, would you arrive at a combined number (tested as a system) than is consistent with the rating?

 

[Andyw2100]

So, just curious for the folks signing the letter....

It would appear to be industry practice to present total horsepower as the sum on the motors/engines in the drivetrain: the BMW says the i8 is 357hp (129hp + 228hp) and Ferrari says the LaFerrari is 963 cv (800cv + 163 cv). So, if Tesla provides documentation of the horsepower of the two motors on the original P85D (470hp on the rear and 221hp on the front), will they be satisfied that Tesla delivered the 691hp car per the published spec?

I saw this post earlier, shortly after you made it, and didn't respond immediately, hoping one of the people more qualified to answer you (like sorka or wk057) would. Since neither of them have, I'll take a crack at it.

I would not be satisfied if Tesla merely demonstrated that each of the motors could independently make 470 and 221 HP. The car, as an entire system, should be able to make the advertised horsepower.

Taking the point you were making a step further, I believe your point might have been that Tesla could have been advertising the maximum horsepower each motor was capable of providing on its own, without being constrained by the limitations of the battery, the fuse, etc. But assuming that was the case, how would you explain the fact that the same two motors, according to Tesla, can now make 503 and 259 HP respectively in the P90D, or in the P85D once upgraded to Ludicrous mode? Clearly those numbers did not represent the max horsepower the motors were capable of, since they are now capable of more.

 

[dsm363]

His question is if the combined output at the shafts equal to that number. For example, if you dynoed at the wheels and accounted for losses, would you arrive at a combined number (tested as a system) than is consistent with the rating?

Thanks. That's what I meant to ask. While Tesla should be better it would at least show they weren't the first company in the world to ever do this.

 

[dsm363]

I saw this post earlier, shortly after you made it, and didn't respond immediately, hoping one of the people more qualified to answer you (like sorka or wk057) would. Since neither of them have, I'll take a crack at it.

I would not be satisfied if Tesla merely demonstrated that each of the motors could independently make 470 and 221 HP. The car, as an entire system, should be able to make the advertised horsepower.

Taking the point you were making a step further, I believe your point might have been that Tesla could have been advertising the maximum horsepower each motor was capable of providing on its own, without being constrained by the limitations of the battery, the fuse, etc. But assuming that was the case, how would you explain the fact that the same two motors, according to Tesla, can now make 503 and 259 HP respectively in the P90D, or in the P85D once upgraded to Ludicrous mode? Clearly those numbers did not represent the max horsepower the motors were capable of, since they are now capable of more.

They should be able to do so but the point is with hearing that might not be possible. I thought the bigger the battery the more power assuming the motors can handle it (might be wrong here). Sounds like the motors are able to handle the additional power.

 

[Andyw2100]

His question is if the combined output at the shafts equal to that number. For example, if you dynoed at the wheels and accounted for losses, would you arrive at a combined number (tested as a system) than is consistent with the rating?

Thanks. That's what I meant to ask. While Tesla should be better it would at least show they weren't the first company in the world to ever do this.

I think some of us would be pretty much OK with Tesla's claims of 691 HP for the P85D if it turned out that dynoed at the wheels, and after accounting for losses, the car actually did make 691 HP initially. It is our contention that at no point does the car make the 691 HP, based on the fact that at no point does the battery put out more than 415 kW.

 

[omarsultan]

His question is if the combined output at the shafts equal to that number. For example, if you dynoed at the wheels and accounted for losses, would you arrive at a combined number (tested as a system) than is consistent with the rating?

A fine question to ask. Testing a single motor/engine is straightforward as you can mechanically connect the shaft to the dyno so there is no squishiness in that number (the SAE testing spec pretty tightly controls variables like fuel, temp, air etc to avoid folks trying to game the system). I don't think anyone publishes hp at the wheel as their are too many variables (transmission, differential, tires, dyno rollers), but IIRC, when I used to be more into this closely, the difference between power at the shaft and power at the wheel tends to be around 15%-20%. For example I have seen the 700hp Hellcat pulling in the 620hp range on the dyno.

It seems that manufacturers are summing the individual output when reporting the total vehicle output. Beyond Tesla, Ferrari and BMW, Porsche does something similar with the 918, but its a little squishier as the rear wheels are driven by both the ICE and the motor.

 

[Andyw2100]

They should be able to do so but the point is with hearing that might not be possible. I thought the bigger the battery the more power assuming the motors can handle it (might be wrong here). Sounds like the motors are able to handle the additional power.

The Ludicrous upgrade of P85Ds to Ludicrous mode doesn't involve an upgrade to a bigger battery. It involves a new fuse and new inconel contactors that will allow more power to flow from the battery at one time.

When the upgrade was announced and explained it helped crystallize the arguments people had been making for some time about the missing horsepower.

I personally really think what is now the Ludicrous upgrade was originally going to be done through software only, and was the "high speed performance improvement" promised on the website. My thinking is that through various testing, etc., Tesla determined that they couldn't open things up enough without risking a fuse and/or contactor failure rate that would be unacceptable, so to provide the power necessary they had to replace the fuse and the contactors. The question is how much kW and how much horsepower the upgrade really allows.*

* I may be flubbing on some of the terminology (I don't know if a fuse failing is correct, for example), as this is not my area of expertise, but the gist of the above should be correct.

 

[dsm363]

You're right. I was thinking about the P90DL vs P85D. The fuses are the difference.

 

[stopcrazypp]

Taking the point you were making a step further, I believe your point might have been that Tesla could have been advertising the maximum horsepower each motor was capable of providing on its own, without being constrained by the limitations of the battery, the fuse, etc. But assuming that was the case, how would you explain the fact that the same two motors, according to Tesla, can now make 503 and 259 HP respectively in the P90D, or in the P85D once upgraded to Ludicrous mode? Clearly those numbers did not represent the max horsepower the motors were capable of, since they are now capable of more.

In the context of the question you were responding to it could be:
1) They measured the power of the rear motor with the battery attached and got a number. They measured the power of the front motor with the battery attached and got a number. They then added the two numbers together. This is essentially what omarsultan says other manufacturers are doing with their numbers. In such a procedure, the change in the fuse/contactor will mean the numbers they measure are higher for each individual motor (assuming the motors can handle it).

2) They measured motor on a motor dyno with a power supply, but they underrated their motors during the first go for whatever reason. Many possible reasons: firmware updates to motor controller later on, raising thermal envelope (allowing the motors to run a little hotter than before), new fuse/contactors at battery changing thermal parameters for motor (instead of assuming the fuse heats up significantly, now it's no different from a section of cable).

 

[Andyw2100]

In the context of the question you were responding to it could be:
1) They measured the power of the rear motor with the battery attached and got a number. They measured the power of the front motor with the battery attached and got a number. They then added the two numbers together. This is essentially what omarsultan says other manufacturers are doing with their numbers. In such a procedure, the change in the fuse/contactor will mean the numbers they measure are higher for each individual motor (assuming the motors can handle it).

If I understand what you are suggesting, then am I correct that if what you are suggesting is true, since the horsepower output of the bigger motor increased when more kW was supplied, then originally the two motors together could never have been producing more horsepower than the large one alone was capable of producing?

Editing to try to explain this better:

Under your scenario, the first motor, when being tested, was getting all the kW the battery, contactor, etc. could supply. Subsequently, with a new contactor and fuse, it gets more kW, and produces more horsepower. So it stands to reason that if it was getting all the kW the battery and contactor could supply when it was tested at 470 HP, the car could never make more than that 470 HP (if your scenario is really what happened) because there was no more kW available beyond what it took to get the larger motor to produce 470 HP.

 

[omarsultan]

Again, we are back stuck pondering exactly how Tesla got two 691hp. Personally, I do think 691 is a defensible number if they are hooked both motors up to the same pack at the same time.

As I have said before, if we assume the pack produces 400V at the pack terminals (a supposition some question) and the 1,300A that Elon mentioned, then we are in 520kW/691hp territory, but as discussed, there are a number of suppositions built into this.

I think it might be worthwhile pondering what would satisfy you on this front--you said something about showing the system delivering 691hp but I think that might be a bit of a squishy concept as the two drive units deliver power independently and are only mechanically coupled via the chassis. For example if they can show ~520kW flowing out of the pack, is that sufficient? I'd imagine a mechanical or drivetrain engineer and a lot of math could show how the two drive units interact to deliver hp to a virtual shaft.

My interest is piqued as to how this all plays out.

 

[Andyw2100]

I think it might be worthwhile pondering what would satisfy you on this front--you said something about showing the system delivering 691hp but I think that might be a bit of a squishy concept as the two drive units deliver power independently and are only mechanically coupled via the chassis. For example if they can show ~520kW flowing out of the pack, is that sufficient? I'd imagine a mechanical or drivetrain engineer and a lot of math could show how the two drive units interact to deliver hp to a virtual shaft.

I'll be satisfied if the guys that understand this a heck of a lot better than I do are satisfied.

I've said several times before that I never would have known the car did not make 691 HP were it not for the knowledge and posts of people here. But what they have said makes sense to me.

Personally, I do not need to see 691 HP at the wheels to be satisfied. I have learned enough from reading hundreds of these posts to understand the significance of drive train loss, etc. One of my concerns, though, is what happens if and when the car is eventually tested on a dyno by a respected source and found to make substantially less than 691 HP at the wheels. How is that going to sound to the general public? (There are dynos capable of accurately representing the horsepower of dual motor cars.)

My interest is piqued as to how this all plays out.

Mine too.

 

[Alipapa]

It is surprising how there are still people trying to defend Tesla on this issue.

The fact is plain and simple: The battery pack is not outputting enough power to the motors to produce the advertised 691HP. Consumer report shows the 0-60 time is 3.5sec instead of the advertised 3.1 sec (12% slower, and yes that does matter, because that's what people paid for)

Isn't this is false advertisement?

I can only imagine how people will react differently if this was done by BYD, or Aston Martin lol

 

[JohnSnowNW]

It is surprising how there are still people trying to defend Tesla on this issue.

The fact is plain and simple: The battery pack is not outputting enough power to the motors to produce the advertised 691HP. Consumer report shows the 0-60 time is 3.5sec instead of the advertised 3.1 sec (12% slower, and yes that does matter, because that's what people paid for)

Isn't this is false advertisement?

I can only imagine how people will react differently if this was done by BYD, or Aston Martin lol

It's un-surprising that you ignore the facts to fit your viewpoint. CR doesn't do the roll out, they specifically mention this. Several other automotive publications have gotten the advertised specs, and one has gotten better.