Model S Performance vs BMW M5

[WarpedOne]

I've put together a chart of Tesla's available power depending on speed. I've added a chart of two typical ICEs with 6-speed gearbox and same maximum power as Roadster and Model S.

What is obvious is that Model S (green thick line) is *much* more powerful than Tesla Roadster (black line), especially at higher speeds.
It is also obvious that fixed-gear transmission is hindering performance of both.
That "constant power" of electric motor is not that constant but it slowly drops until it suddenly almost vanishes. Classical transmission on the other hand really delivers that maximum power in every "speed interval".

So, when a ICE sports car is spiritedly driven, it is faster than en 'equivalent' EV with only a reduction gearbox.
But when both ICE and an EV is in the hands of inexperienced or lazy driver who doesn't wont to constantly push ICE above 5k RPM, an EV one will perform better, because power is always there. You don't have to 'summon' it. Rocket ship versus bucking bronco is a very good description. ICE power is explosive, always coming and going, EV power feels always there until you go to fast.

Roadster' max power should suffice for about 270 km/h (165mph) top speed. A singlespeed gearbox that is necessary for such speed would feel week in normal driving. 0-60 time would be over 10s.

Model S' max power should suffice for 300 km/h (185 mph). But again the limit is fixed gear transmission.

 

[CapitalistOppressor]

You hit the nail on the head on this one.

Short of only comparing the cars at tracks where the top speed will be below 100mph (Summit Point Jefferson circuit in WV comes to mind) this comparison of track prowess is pointless. I have raced cars and motorcycles for the better part of 12 years and top speed (track dependant, of course) has a huge impact. I race motorcycles and my GSX-R750 will repeatedly get destroyed by 1000cc bikes on topend. Depending on rider, I can hang in the corners but once we hit a straight the topend difference is the deal-breaker. My bike can only do 174mph and litre bikes can get up to 190+mph (and get there quicker).

I totally agree in all respects. So lets make sure the first YouTube videos to come out are from Summit Point instead of Pomona Drag Strip ..

 

[W8MM]

Model S apparently doesn't have the same heating issues above 70MPH that the Roadster had. I've seen numerous reviews stating that Model S is accelerating through 100 with authority. MotorTrend specifically compared it to a "big gasser" in that respect. We badly need instrumented tests for actual data, but I suspect that based simply on basic physics of transmissions vs direct drive that Model S can't match a modern gas vehicle in 100+MPH acceleration.

The Roadster employed a trick in the inverter circuit that made it act like an "electronic transmission". In order to increase the current to the motor past the maximum safe current delivery of the battery pack, the inverter was configured to function as a "bucking" switch-mode power supply and increase the current while reducing the effective voltage supply. This works very well at low speeds and provides all the effect of a "first gear" while mechanically driving around in "second". The method "runs out of gas" at higher speeds where the electric motor's back-EMF closes in on the reduced supply voltage and has to be abandoned. It's a smooth transition, programmed into the inverter's load vs. RPM map.

No doubt something like this, only better, is employed in the Model S. In fact, I'll speculate that the Performance option is really composed of an inverter module with more aggressive "electronic transmission" programming and bigger or many more in parallel IGBT switching elements to accommodate the higher motor currents involved.

Edit: The Performance option may also include the "more copper" motor variation seen in the Roadster.

 

[CapitalistOppressor]

I've put together a chart of Tesla's available power depending on speed. I've added a chart of two typical ICEs with 6-speed gearbox and same maximum power as Roadster and Model S.

What is obvious is that Model S (green thick line) is *much* more powerful than Tesla Roadster (black line), especially at higher speeds.
It is also obvious that fixed-gear transmission is hindering performance of both.
That "constant power" of electric motor is not that constant but it slowly drops until it suddenly almost vanishes. Classical transmission on the other hand really delivers that maximum power in every "speed interval".

So, when a ICE sports car is spiritedly driven, it is faster than en 'equivalent' EV with only a reduction gearbox.
But when both ICE and an EV is in the hands of inexperienced or lazy driver who doesn't wont to constantly push ICE above 5k RPM, an EV one will perform better, because power is always there. You don't have to 'summon' it. Rocket ship versus bucking bronco is a very good description. ICE power is explosive, always coming and going, EV power feels always there until you go to fast.

Roadster' max power should suffice for about 270 km/h (165mph) top speed. A singlespeed gearbox that is necessary for such speed would feel week in normal driving. 0-60 time would be over 10s.

Model S' max power should suffice for 300 km/h (185 mph). But again the limit is fixed gear transmission.

View attachment 7207

Your post is a thing of beauty. I should turn it into a poster

 

[brianman]

I'm confused by this. Perhaps some one can clarify.
Audi R8 e-tron sets new electric record* with 8:09.099 time at Nrburgring

It's not a new fastest EV ever record, but Audi has just set a new "series production electric car" speed record

The R8 EV isn't due until the end of the year, but the powertrain in the record-setting car, "corresponds in every detail with that of the production model," says Audi.

There were some differences, though, including that the top speed was raised to 250 kilometers an hour (155.34 miles per hour) instead of the usual 200 kmh (124.27 mph).

Ok, so, let me see if I got this straight.

It's a production car record. But it's not a production car (much less available). But it's the same specs as a production car. But it has a different top speed limiter.

Ok so they've set the "production record" for a vehicle that's (a) unavailable to a consumer, (b) the same as production car, and (c) different from production car.

I call bullshit.

 

[W8MM]

There's a different optimum gear ratio (linked to top speed of car) for every race track in existence. Audi's racing department probably used many hours of computer simulations to determine the exact final drive ratio that would result in the quickest lap times after considering the available motor characteristics, the grip of the special tires used, the aerodynamics of the car, etc., ad nauseum, matched to the known geography of the track.

The ratio diverges from the stock car's specs because the drag race numbers (0-60, 1/4 mile, etc.) that are important for marketing the car require a different final drive ratio than the one for minimum lap times on the Nordschleife. Some other race track would require a different final drive ratio, and therefore yet another, different top speed.

 

[brianman]

Unless an "average joe" can buy one with the exact configuration used on the track, it shouldn't be heralded as a "production car" record. Period. IMO.

Reminds me of Bill Clinton's primer on the English language.

 

[W8MM]

Welcome to the world of auto company PR :wink:

 

[Jason S]

There's a different optimum gear ratio (linked to top speed of car) for every race track in existence. Audi's racing department probably used many hours of computer simulations to determine the exact final drive ratio that would result in the quickest lap times after considering the available motor characteristics, the grip of the special tires used, the aerodynamics of the car, etc., ad nauseum, matched to the known geography of the track.

The ratio diverges from the stock car's specs because the drag race numbers (0-60, 1/4 mile, etc.) that are important for marketing the car require a different final drive ratio than the one for minimum lap times on the Nordschleife. Some other race track would require a different final drive ratio, and therefore yet another, different top speed.

The end of the article describes lap times "with the speed limiter left intact". Therefore it could be production just without the production speed limiter.

 

[W8MM]

The end of the article describes lap times "with the speed limiter left intact". Therefore it could be production just without the production speed limiter.

They said a second car had the speed limiter intact. Could be merely electronic or it could be literary license about what exact bits on the car limit its speed.

 

[PV4EV]

...
After 3 Porsches, 4 Ferraris, 2 TVRs, 3 Lotus'es, 4 Group B rally cars, 2 Astons, 2 RS6's, 2 Quattro's, various track cars, 1 BMW (!) and dozens of hot hatch backs etc, and around 2,000+ miles in a BMW M5 V10 …. I just do not want any more ICE cars ... no matter how brilliant they might be round The Ring.

After 1 Tesla, I doubt I will ever buy another ICE car ever again. I just don’t see the point of them anymore.

This was just beautiful.

sniff!

Thanks :biggrin:

 

[CapitalistOppressor]

Your post is a thing of beauty. I should turn it into a poster

Lack of a transmission aside, it seems to me that the fundamental limitation to Model S acceleration is the power output of the batteries, which need to be balanced against storage requirements. Aside from dealing with the heating issues that Roadster had above 70mph the big performance boost for Model S is the ~40% increase in storage density and the associated increase in power output.

In 4 years a hypothetical Model S v2.0 with a ~40% improvement over current batteries will be able to gear itself for substantially higher top end performance without losing much low speed acceleration, where you are limited by traction. But no matter how much you improve that you are limited somewhere because of the single gear ratio. The parts will break if you torque them enough to achieve high low end acceleration with a really long gear ratio. So super car status might not ever be achievable with a direct drive EV. But for any performance regime legally accessible Model S already looks to be a very strong competitor.

Roadster v2.0 isn't on the radar yet, but when they do it they will want it to be a world beater. They will probably have batteries twice as good as Roadster 1 while also being able to optimize it for weight by using aluminum and carbon fiber. They will have weight margin and space available to spend on a transmission.

 

[WarpedOne]

Speed limiter on a ICE vehicle is something completely different than speed-limiter on a single-ratio gearbox vehicle.

Speed limiter in ICE car is purely a *bureaucratic* limit on what you may do. If you remove it, no part will be stressed above its design limitations, vehicle will just gain speed until it hits its power wall (sum of all kinds of "drags") or RPM limiter. In 4th gear you would only run into RPM limiter, in 6th you run into speed limiter first.

In single-speed gearbox the RPM limiter doubles as a speed limiter. If you remove it, electric motor could spin to fast and brake apart just like ICE engine does if it exceeds its safe design RPM.

Remember that forces acting upon rotor in the motor increase linearly with square of RPM. 10% higher RPM produces 21% stronger forces that want to tear it apart. Add high temperatures because of high currents and problems are even nearer.

How much reserve strength is there in the rotor (i.e. how higher RPM it could take without physical damage) is not something that Tesla will say aloud. Some other aluminum AC motor with much less power that goes upto 11k powered RPM has 12k RPM mechanical limit - i.e. if you allow it to spin faster it may brake apart sooner or later.

So super car status might not ever be achievable with a direct drive EV.

Truth be told, yes
High-power speed range is much wider than with ICE engine in any given gear but it still has its on-ramp and diminishing ranges that aren't that stellar as that middle range. Supercar version would need a 3-speed automatic transmission, 1st would double the "current 2nd speed ratio", the third would halve it.
Acceleration in 1st would be brutal, top speed in 3rd autobahn-king-like, everyday drive-ability in 2nd just like today.
It would add very little weight and demand just a little additional space, but RD looks like a big problem, something Magna nor someotherOEM could pull of with roadster.

 

[TEG]

Speed limiter in ICE car is purely a*bureaucratic* limit on what you may do. If you remove it, no part will be stressed above its design limitation, vehicle will just gain speed until it hits its power wall (sum of all kinds of "drags") or RPM limiter...

Um, tend to disagree. Sometimes ICE cars have a speed limiter ("Governor") because they don't want to exceed the rated safe speed of the tires, or there are issues with aerodynamic lift at high speeds. Other reasons too.

 

[TEG]

Roadster v2.0 isn't on the radar yet, but when they do it they will want it to be a world beater. They will probably have batteries twice as good as Roadster 1...

Um, technically we already have "Roadster 2" as Tesla used that designation for all the changes they made between the 2008 and 2010 model year.
I think it would be more correct to refer to the next Roadster as "Roadster 3.0"

 

[brianman]

It would be interesting if Tesla (or a 3rd party) built a "concept" Model S with high charge/discharge rate batteries instead of endurance batteries.

It would also be interesting for straight line tests to put additional batteries in the frunk and passenger areas.

 

[WarpedOne]

Lack of a transmission aside, it seems to me that the fundamental limitation to Model S acceleration is the power output of the batteries, which need to be balanced against storage requirements.

Not really. Power drawn from the batteries is just a tad higher than power put to the wheels (heating losses, ...).
Model S attains its max power at 95 kmh (58 mph). All acceleration below this speed 'happens' at lower power and lower battery output. Average power for 0-60 time is about half the peak power.

If Model S or Roadster or any car had some "magic CVT" that allowed the engine/motor to stick to its max power RPM all the time, 0-60 time would be half the current time with same load onto the batteries. I'm ignoring time limits in allowed high-C currents and assuming enough grip.

If on the other hand you would double the battery output, the curve would only be higher, not wider.

 

[J in MN]

I've put together a chart of Tesla's available power depending on speed. I've added a chart of two typical ICEs with 6-speed gearbox and same maximum power as Roadster and Model S.

Thank you, but it would be much more insightful to see the torque vs speed, instead of power vs speed, since acceleration is proportional to force/torque, not power.

 

[vfx]

Um, technically we already have "Roadster 2" as Tesla used that designation for all the changes they made between the 2008 and 2010 model year...."

And it's aluminum and Carbon Fiber.

 

[Lyon]

This was just beautiful.

sniff!

No kidding, I was ready to vote for him, go knock on doors and write a check to the campaign!