200 kWh Roadster Pack: How is Tesla Pulling This Off?

[strider]

You're making extraordinary claims that somehow less mass is bad for handling, so you need to come up with extraordinary evidence.

@Peteski never said that. On the contrary he said the exact OPPOSITE of that. He said that the most important thing for handling is reducing mass. The placement of that mass then has more to do with how the driver controls the car than its absolute capability. He has been incredibly consistent in his statements. You are intent on talking about hypotheticals (0 inertia, WTF is that?) when he is talking about the real world. You know, the one where we all live and cars exist.

@Peteski, you keep talking about the 919. Isn't that a proper race car, not a road car? Shouldn't we be comparing the v4 Roadster to the 918 since that is street legal?

 

[AWDtsla]

@Peteski never said that. On the contrary he said the exact OPPOSITE of that. He said that the most important thing for handling is reducing mass. The placement of that mass then has more to do with how the driver controls the car than its absolute capability. He has been incredibly consistent in his statements. You are intent on talking about hypotheticals (0 inertia, WTF is that?) when he is talking about the real world. You know, the one where we all live and cars exist.

Yeah I'm getting nowhere with the theoretical arguments. The point of 0 inertia is to test his "theory" at the limits. Turns out, there isn't any theory, just bluster.

Elon Musk disagrees with this idea and so do I. We'll leave it at that since the theoretical discussion is dead.

 

[Peteski]

Yeah I'm getting nowhere with the theoretical arguments. The point of 0 inertia is to test his "theory" at the limits. Turns out, there isn't any theory, just bluster.

Elon Musk disagrees with this idea and so do I. We'll leave it at that since the theoretical discussion is dead.

You are getting nowhere with your argument because it's totally incoherent and you clearly don't even understand my own "theory" which is actually just basic physics. I've been fortunate enough to work with the best of the best motorsport engineers over the years and this is our bread and butter. I'm not saying anything revolutionary here. You are the one talking about infinite this and zero that and then mixing them up randomly to suit your argument. Then you have the audacity to suggest that I don't think less mass would improve handling. You honestly couldn't make it up, lol!

 

[Peteski]

[USER=66251]@Peteski, you keep talking about the 919. Isn't that a proper race car, not a road car? Shouldn't we be comparing the v4 Roadster to the 918 since that is street legal?[/USER]

Yeah, I only used the 919 as an extreme example since it recently obliterated the Nurburgring lap record. The 918 is I think some 700kg heavier and therefore a lot slower around the Ring. I just don't fancy the chances of a 2000+ kg Roadster being competitive in lap time. I think the 918 is around 1600 kg, so not exactly a lightweight itself. If the Roadster can come in below 1700 kg then it could be very respectable, but unlikely to break any lap records except maybe beat the Nio EV record. But can it even be that light with a 200 kWh battery? I doubt it based on what we know so far.

 

[Peteski]

blah blah blah blah, no theory in reply.

Just go back and re-read the last few pages and then tell me your comments make any coherent sense. I don't think you're fooling anyone here.

 

[Peteski]

You're a troll. I engaged you in a theoretical discussion, and you keep coming back with big piles of nothing.

It's impossible to have a meaningful theoretical debate with someone who seems to think I said the exact opposite of what I did! Other posters have even called you out on it and yet you seem oblivious. As for your own theoretical argument I don't even vaguely understand your position and I don't think anyone else does either.

Calling me a troll isn't going to get you anywhere either. Nobody in their right mind would accuse me of trolling here, whether they agree with me or not.

 

[strider]

Yeah I'm getting nowhere with the theoretical arguments. The point of 0 inertia is to test his "theory" at the limits. Turns out, there isn't any theory, just bluster.

Elon Musk disagrees with this idea and so do I. We'll leave it at that since the theoretical discussion is dead.

You are the one that is engaging in theoretical arguments while @Peteski is making factual points about the real world. You're acting like a child.

Elon is a lot of things but he is NOT an expert on vehicle dynamics. Very far from it in fact. Current EVs are heavy, that's just a fact. They hide their weight very well due to their low CG but heavy is heavy.

 

[CarlK]

You are the one that is engaging in theoretical arguments while @Peteski is making factual points about the real world. You're acting like a child.

Elon is a lot of things but he is NOT an expert on vehicle dynamics. Very far from it in fact. Current EVs are heavy, that's just a fact. They hide their weight very well due to their low CG but heavy is heavy.

Not sure you understand it either. "Weight" is just a small part of the equation. It's so important in traditional cars only because all other possible improvements have pretty much been exhausted. The example I mentioned that 4000 lb Model 3 "track mode" could match the 3000 lb GT4 with probably the best track tuning on the market should give you something to think about.

 

[3mp_kwh]

Too bad, seeing the thread break down.

Elon is a lot of things but he is NOT an expert on vehicle dynamics. Very far from it in fact. Current EVs are heavy, that's just a fact. They hide their weight very well due to their low CG but heavy is heavy.

It's great Probst could work out improvements to Track Mode, but it makes clear what probably shouldn't surprise anyone. The young company's priorities are in the right place, and not a lot of high level speed time has come at the hands of pro drivers. That, alone, makes me believe Roadster isn't far as a "lap car", which goes hand in hand with 200KWh making it a high mass car, and so on.

M3P gives Cayman a run because it really isn't that heavy a car. ~3,800lb isn't a heavy passenger car, anymore (4k AWD?). Porsches are getting heavy. The PHEV Panemera has just 14KWh, and Porsche let it climb over 5,000lb. The GT3s, aren't much lighter than the 3,200lb generic 911s. Go for the turbo, and you're already nearing Model 3 weight again.

All this said, I'd take the NIO over the GT2 RS, or the 918, any day. I like bragging the 919's record shattering 'Ring time was ultimately done by a hybrid, but only to people whose sphere is limited to ICE. On TMC, people know what's become of Volkswagen Group and realize there's not much electric going on, there. The 919 has ground effects, and all the downforce that goes along with monstrously increasing grip. It's silly level stuff, for people whose minds would be blown by any time in the 7's (including mine). The energy density of batteries is going to be a sticking point for die hard internet discussions, for a number of years to come. I'm just glad I'm passed it, and know that even current batteries would be fine, if we could just get better track-side charging.

 

[ecarfan]

Moderator note: 3 posts removed for inappropriate language. Member has been warned.

To those of you who are having a civil discussion, thank you. Carry on...

 

[FlatSix911]

Too bad, seeing the thread break down.

All this said, I'd take the NIO over the GT2 RS, or the 918, any day. I like bragging the 919's record shattering 'Ring time was ultimately done by a hybrid, but only to people whose sphere is limited to ICE. On TMC, people know what's become of Volkswagen Group and realize there's not much electric going on, there. The 919 has ground effects and all the downforce that goes along with monstrously increasing grip. It's silly level stuff, for people whose minds would be blown by any time in the 7's (including mine). The energy density of batteries is going to be a sticking point for die-hard internet discussions, for a number of years to come. I'm just glad I'm passed it and know that even current batteries would be fine if we could just get better track-side charging.

I would recommend trying the 918 on the basis of the investment potential and then purchase a few Roadsters with the appreciation

 

[Peteski]

Not sure you understand it either. "Weight" is just a small part of the equation. It's so important in traditional cars only because all other possible improvements have pretty much been exhausted. The example I mentioned that 4000 lb Model 3 "track mode" could match the 3000 lb GT4 with probably the best track tuning on the market should give you something to think about.

Weight is a fundamental parameter, not just a small part. Mass is central to even the most basic vehicle dynamics model. Of course it's not the only parameter and EVs have some inherent advantages, but weight is their major downside and a 200 kWh battery will only make this worse.

If you are serious about setting track records you can't be giving away hundreds of kgs. Even with less power a 100 kWh "lightweight" Roadster will eclipse a 200 kWh version around any road track. Ultimate road track racers like the 919 are all well under 1000 kg, but their road counterparts tend to be up around 1600-1700 kg. This is where the Roadster needs to be, not well north of 2000 kg.

 

[mongo]

Weight is a fundamental parameter, not just a small part. Mass is central to even the most basic vehicle dynamics model. Of course it's not the only parameter and EVs have some inherent advantages, but weight is their major downside and a 200 kWh battery will only make this worse.

If you are serious about setting track records you can't be giving away hundreds of kgs. Even with less power a 100 kWh "lightweight" Roadster will eclipse a 200 kWh version around any road track. Ultimate road track racers like the 919 are all well under 1000 kg, but their road counterparts tend to be up around 1600-1700 kg. This is where the Roadster needs to be, not well north of 2000 kg.

Cutting the pack capacity in half means cutting max pack power and thus max motor power in half, along with regen. The same mass reduction in an ICE would likely not means less power. So it depends on the course and if more than double the theoretical acceleration (twice the power but not twice the weight), assuming motor capacity, and a 26% ish higher top speed (aero power being cube of speed) is more of an impact than the need to slow more for turns.
Of course, if the performance is motor limited at 100kWh, then more battery doesn't help at all, but I doubt it is.

Edit: In the short term, double the pack also means roughly double the thermal mass to use to keep the drive units cool, assuming similar track mode features to the 3 and an appropriate length track.
Speaking of track length, a larger pack also means less SOC/ voltage loss and longer duration with equivalent performance to the start of the first lap.

Edit x2 : Its roughly equivalent to reducing both the gas tank and fuel line by 50% (line reduction being flow at pressure, not physical diameter).

 

[Peteski]

Cutting the pack capacity in half means cutting max pack power and thus max motor power in half, along with regen. The same mass reduction in an ICE would likely not means less power. So it depends on the course and if more than double the theoretical acceleration (twice the power but not twice the weight), assuming motor capacity, and a 26% ish higher top speed (aero power being cube of speed) is more of an impact than the need to slow more for turns.
Of course, if the performance is motor limited at 100kWh, then more battery doesn't help at all, but I doubt it is.

Edit: In the short term, double the pack also means roughly double the thermal mass to use to keep the drive units cool, assuming similar track mode features to the 3 and an appropriate length track.
Speaking of track length, a larger pack also means less SOC/ voltage loss and longer duration with equivalent performance to the start of the first lap.

Edit x2 : Its roughly equivalent to reducing both the gas tank and fuel line by 50% (line reduction being flow at pressure, not physical diameter).

I don't think you would be cutting power in half although it would have some impact. I don't think the Nio has a pack larger than 100 kWh and that still produces well over 1000 hp. Once you get to that sort of power level simply adding more and more doesn't really buy you much lap time and certainly not with a large weight penalty. Ultimately it's the tyres that give out first when faced with massive power and a huge amount of weight. It reminds me a little of the 1500 hp qualifying engine era in F1. They used to destroy their tyres halfway around the first flying lap and that was with no extra weight at all. In a contemporary supercar with that kind of power you would be just working the traction control systems harder and harder as you added more power.

It's all a compromise and what Elon is doing with the Roadster is focusing on straight line performance and glossing over the fact that it will hurt the ultimate handling due to all that extra weight. It might still be a great roadcar, just not the ultimate track day weapon. Laptime is the one metric likely to elude BEVs for quite some time IMHO.

Porsche are well aware of these limitations and why they are still on the fence about designing a BEV 911. With the Taycan weight is not such a major problem given the target market for that car. When they start producing more track focused BEVs they are not likely to feature huge capacity batteries or insane power. But they will produce quick lap times.

 

[Peteski]

Looking at the spec of the Nio EP9, that is actually going to be a very tough challenge for the Roadster to beat in lap times. It has a full carbon race-bred chassis, 4 motors, torque vectoring and serious downforce. Probably overkill for the Nurburgring and still a bit too heavy at 1735 kg, despite a modest battery capacity. I actually know their chief engineer personally, but I haven't discussed it with him.

 

[Dr. J]

So you actually think professional engineers with a University education don't understand basic physics? Yeah sure, whatever.

Howard Wolowitz, meet Sheldon Cooper.

 

[mongo]

I don't think you would be cutting power in half although it would have some impact. I don't think the Nio has a pack larger than 100 kWh and that still produces well over 1000 hp. Once you get to that sort of power level simply adding more and more doesn't really buy you much lap time and certainly not with a large weight penalty. Ultimately it's the tyres that give out first when faced with massive power and a huge amount of weight. It reminds me a little of the 1500 hp qualifying engine era in F1. They used to destroy their tyres halfway around the first flying lap and that was with no extra weight at all. In a contemporary supercar with that kind of power you would be just working the traction control systems harder and harder as you added more power.

It's all a compromise and what Elon is doing with the Roadster is focusing on straight line performance and glossing over the fact that it will hurt the ultimate handling due to all that extra weight. It might still be a great roadcar, just not the ultimate track day weapon. Laptime is the one metric likely to elude BEVs for quite some time IMHO.

Porsche are well aware of these limitations and why they are still on the fence about designing a BEV 911. With the Taycan weight is not such a major problem given the target market for that car. When they start producing more track focused BEVs they are not likely to feature huge capacity batteries or insane power. But they will produce quick lap times.

Agree, lots of trade offs.
Couple points in that realm, at low speed power is limited by traction due to max traction available. Mass fights down force as the tire grip to force ratio is less than 1. At high speed, aero resistance is the thing acting against tire friction, so mass helps (for same aero down force), and power improves top speed. (Assuming a long enough straightaway).

Tire shredding should not be an issue on any EV since motor speed is basically instantly controllable to limit/prevent wheel slip, skidding on corners is still an issue though, but the system can minimize the extra tire shedding rotations when the rubber breaks free.

 

[Peteski]

Agree, lots of trade offs.
Couple points in that realm, at low speed power is limited by traction due to max traction available. Mass fights down force as the tire grip to force ratio is less than 1. At high speed, aero resistance is the thing acting against tire friction, so mass helps (for same aero down force), and power improves top speed. (Assuming a long enough straightaway).

Tire shredding should not be an issue on any EV since motor speed is basically instantly controllable to limit/prevent wheel slip, skidding on corners is still an issue though, but the system can minimize the extra tire shedding rotations when the rubber breaks free.

Tyre wear and stress will always be higher with a heavier car as you are loading the tyres more, both in lateral and longitudinal acceleration, regardless of slip. If you are pulling 1.5G around a corner, the tyres have to produce a lateral force equivalent to 1.5 x total weight. Pull 2.0G on the brakes and the tyres have to produce a force of 2 x total weight. More vertical tyre load produces more grip, but it's a flattening curve against increased weight, not linear, so you always lose out on balance with increased mass. Not to mention the need for ever higher tyre pressures and stiffer suspension as you add more and more weight. All these things are detrimental to performance and handling, which is why focused race cars are always made as light as they possibly can be without compromising structural integrity.

Going back to the fundamental issue with performance EVs (high battery weight), having an inherently low CofG height (a genuine benefit since it reduces lateral weight transfer when cornering) and a relatively low mass moment of inertia (although a battery is not exactly a point mass, taking up the whole floor pan area!) are positive things, but they can only go so far in compensating for the absolute mass. So Tesla are really pushing their luck fitting a 200 kWh battery if they expect to achieve competitive track handling. It's one thing compensating for say 100 or even 200 kg of weight compared to the competition (as we've seen with the M3P), but the Roadster is going to be up against some serious ICE and hybrid opposition. The likes of Porsche will push hard just to save 30-50 kg of weight in their track focused models and it does make a difference! We've already seen the Nio EP9 get beaten by ICE rivals (although still a very impressive performance) and that has all the inherent BEV advantages in a very track focused package, plus it only has a sub 100 kWh battery and isn't ridiculously heavy at 1735 kg.

Realistically, how heavy is the Tesla Roaster going to be with a 200 kWh battery and probably not a full carbon fibre chassis and bodywork? It could even be over 2500 kg, which will be a major problem when people start rocking up at tracks with it! It's certainly going to be interesting....

 

[Cloxxki]

At 200kWh, of the same cells as used in Model 3, we can expect around 2.5x as much power. A good MegaWatt, nothing surprising considering S/X P100DL at >500kW, but Model 3 has better power retention it seems which is needed to not look a fool around a lap.
And obviously from the intent to make it really quick off the line and over the 1/4 mi, Tesla are going to make it all available unless there's heat saturation. At top speed, ~500kW could actually suffice for 400kph cruising which along with strong air cooling might be possible for the full 24 minutes/160km/100mi.

I expect nothing from Tesla in the way of meaningful downforce, it will corner AT BEST like a Model 3 on wider stickier tyres as with the same cell but 150% more of them, it will just be a brick of a car. Even Bugatti Chiron may end up lighter and with more downforce AND way better power over a stint. It's a radiator on wheels pretty much. Range at 400kph might be similar for the two, just the Bugatti can go a lot quicker. I know Koenigsegg makes faster cars, but the Bugatti is heavier and AWD.

Tesla could well buy some more sparky cells and get all this power at 55-60% of the pack weight and 100kWh. Just, range would be half. In stead of for instance 2,000kg (if even that light at all), it could be 1500kg and MUCH faster in all conditions. Heat management might also be better with higher C cells. Rimac seems to have that figured out and Porsche (now 10% shareholder in Rimac) at promising largely head loss-less performance for the upcoming Taycan.
In Tesla's case, having slow cells, drawing peak levels from it will cause heat issues but offer some fast numbers. Not necessarily faster race stint (10 or 20 GP laps in a row).

As a performance lover, I'd rather have a 100kWh Roadster than is 500kg lighter for the same output power and has 52% of the range. Especially as it should easily charge to 350kW like Porsche and friends.
A long range car would have been fun 10 years ago. They could have gotten well over 150kWh in a bespoke Roadster back then, even with pre-Mode S 18650's. Oh, and 1,000hp. 200kWh seems an awkward way to convince car buyers that an EV can get far in a time when range anxiety is all but dead.

 

[NeverFollow]

As a performance lover, I'd rather have a 100kWh Roadster than is 500kg lighter for the same output power and has 52% of the range. Especially as it should easily charge to 350kW like Porsche and friends.
A long range car would have been fun 10 years ago. They could have gotten well over 150kWh in a bespoke Roadster back then, even with pre-Mode S 18650's. Oh, and 1,000hp. 200kWh seems an awkward way to convince car buyers that an EV can get far in a time when range anxiety is all but dead.

I was surprised also during the preview that the 2020 Roadster will have a 200 kWh, mostly because of the additional weight,
and also considering the constant improvement of the cells. So there must be some specific reasons to justify it.

Or is it for justifying the price, otherwise a 120 kWh Roadster could have been sold around the price of a 100 Model S or X.

Note: I assume that the next generation of Model S and X will get a 120 kWh. So I think that a Roadster with a single 120 kWh
would be also more optimum to keep cool than two 100 kWh batteries packs placed on top of each other.

Anyway, I can't wait to see some Nurburgring numbers!