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Tesla Roadster

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Re: Tesla Roadster

#481

Post by throwaway76543 »

DennisP wrote: post #417
chrisper wrote: post #71

Earlier quoted context omitted.

Also I wonder how many times you can accelerate like that... maybe only once with full charge?

The Porsche CEO has been sorta claiming that but it doesn't make sense to me. The kinetic energy of your car at a given speed is the same, regardless of how fast you accelerated to get to that speed. Do batteries waste more energy when you drain them faster? They can't waste a large portion of battery capacity, because the heat from that much energy getting wasted would blow up the car.

Drag. Recall, wind resistance is proportional to the square of velocity. The vast majority of energy goes into overcoming drag, even at regular highway speeds. Remember when we capped speed limits at 55mph during the '70s energy crisis? We did so because fuel efficiency really starts to drop off at faster speeds. 250mph is very, very far up this curve.

Wikipedia has a nice graph to illustrate: https://en.wikipedia.org/wiki/File:Chart_MPG_to_L-100km_v200...

Re: Tesla Roadster

#482

Post by clintonb »

rottyguy wrote: post #410
tdiggity wrote: post #131

Earlier quoted context omitted.

Founder series limited to 1000 requires full deposit, that's $250 mil Base model requires $45k deposit. Not sure what semi requirements are. Even if they are biting off more than they can chew, they can gauge reaction and devote more/less to this. I'm thinking that these ventures give their engineers a space to get really creative and push the envelope. And, these advancements make their way into the mainstream model…

What's even more amazing is that F or GM couldn't possibly do this. First mover advantage plus the allure of someone like Musk is what is needed. I know many bash him for spreading himself too thin among all his other ambitions but it gives him good will capital (which can translate to economic capital) when needed.

Ford or GM couldn't possibly do what? Pre-sales? The new Ford GT cost $450K and will only be available to select buyers during the first production year. I imagine GM does something similar with the higher-end Corvettes. Dodge did the same with Viper.

Re: Tesla Roadster

#483

Post by 8draco8 »

Unklejoe wrote: post #480

Has the 8 second quarter mile been confirmed to be done in stock trim (i.e., no special tires or other modifications)? The reason I ask is because that is EXTREMELY impressive. I tune EFI systems on race cars as a hobby, and any car in the 8 second range usually needs to run slicks or drag radials to have enough traction. Even all wheel drive cars (GTRs, DSMs, EVOs, etc.) usually run 4 slicks once they get to that sp…

Yes but in those cars traction control is usually off. In Tesla extremely precise traction control may work in your favour giving only as much power as tires can handle effectively allowing to near zero time loss on regaining tracktion. In quarter mile cars you don't have option, either tire will handle all that power or slip causing time loss.

Re: Tesla Roadster

#484

Post by DennisP »

throwaway76543 wrote: post #481
DennisP wrote: post #417

Earlier quoted context omitted.

The Porsche CEO has been sorta claiming that but it doesn't make sense to me. The kinetic energy of your car at a given speed is the same, regardless of how fast you accelerated to get to that speed. Do batteries waste more energy when you drain them faster? They can't waste a large portion of battery capacity, because the heat from that much energy getting wasted would blow up the car.

Drag. Recall, wind resistance is proportional to the square of velocity. The vast majority of energy goes into overcoming drag, even at regular highway speeds. Remember when we capped speed limits at 55mph during the '70s energy crisis? We did so because fuel efficiency really starts to drop off at faster speeds. 250mph is very, very far up this curve. Wikipedia has a nice graph to illustrate: https://en.wikipedia.or…

True, I was just thinking about quick accelerations to reasonable highway speeds, which is what the Porsche guy was talking about.

Re: Tesla Roadster

#485

Post by TFortunato »

InternetOfStuff wrote: post #292
neya wrote: post #223

Earlier quoted context omitted.

10,000 NM of torque. That's INSANE. I drive a car with 400NM torque and that thing scares the sh*t out of me when I accelerate. 10,000 NM? Isn't that something along the lines of a tram or a train (I'm not sure, I'm asking you guys). This is CRAZY. I'm getting one for sure.

Your car has 400Nm at the engine output shaft. After gearing, you'll have the same order of magnitude torque at the wheels as the Tesla. Randomly picked example: Porsche G97/01 (997 Carrera 2 2005-08) First gear total reduction 13.45 (gear 3.91, rack&pinion 3.44) So, ignoring efficiencies, you'd have a first-gear torque of 400Nm * 13.45 = 5380Nm at the wheels. Still "only" half of the Tesla, but not an earth-shatteri…

Isn't the rack-and-pinion for steering, not for power transmission to wheels?

Re: Tesla Roadster

#487

Post by wyager »

warpdude wrote: post #428
jfindley wrote: post #397

Earlier quoted context omitted.

I agree, I think this is another case of "well it works on our computer" pre-release specs that will turn out not to get close to real-world performance. The 0-100mph is very suspicious but I think the 0-60 time quoted is simply impossible for a road car, even making allowances for a few years of tech advancements. F1 tires are nothing like road tires. They're not even vaguely comparable - at normal operating tempera…

> F1 tires are nothing like road tires. Agreed, but they don't need to be. Remember, the magic number here is ~1.4G, for a 1.9s 0-60. The Pilot Sport Cup 2 – a track-friendly R-compound tire used in the webcast car and in the videos – can pull close to that on a skidpad (i.e. less than optimal conditions), meaning the grip is there. > I think it's straining credulity to believe that an electronic traction control sys…

> namely uneven power delivery and physical limitations on peak RPMs. An electric motor has none of these problems.

Electric motors do actually have an uneven response at different RPMs (in the form of back-emf losses). I worked for a while with an electric car team in university, and we used a mechanical system to adjust the stator position and tune the motor for different RPMs. I’m not sure what Tesla is doing to address this (could be mechanical or solid state), but you definitely can’t just keep dumping more power into a motor and expect it to get correspondingly faster, not even as a reasonable approximation.

Re: Tesla Roadster

#488

Post by Retric »

Vel0cityX wrote: post #455
jfindley wrote: post #397

Earlier quoted context omitted.

I agree, I think this is another case of "well it works on our computer" pre-release specs that will turn out not to get close to real-world performance. The 0-100mph is very suspicious but I think the 0-60 time quoted is simply impossible for a road car, even making allowances for a few years of tech advancements. F1 tires are nothing like road tires. They're not even vaguely comparable - at normal operating tempera…

What about weight? The Roadster is probably quite more more heavy than an F1, doesn't that play a big role in traction?

Not really, wider tires for example let you have constant pressure per surface area in contact with the road.

Now there are minor effects that do come into play, so 100x the weight would be meaningful. But, weight within the range of normal cars is not really important.

Re: Tesla Roadster

#489

Post by bkanber »

TFortunato wrote: post #485
InternetOfStuff wrote: post #292

Earlier quoted context omitted.

Your car has 400Nm at the engine output shaft. After gearing, you'll have the same order of magnitude torque at the wheels as the Tesla. Randomly picked example: Porsche G97/01 (997 Carrera 2 2005-08) First gear total reduction 13.45 (gear 3.91, rack&pinion 3.44) So, ignoring efficiencies, you'd have a first-gear torque of 400Nm * 13.45 = 5380Nm at the wheels. Still "only" half of the Tesla, but not an earth-shatteri…

Isn't the rack-and-pinion for steering, not for power transmission to wheels?

Yes rack and pinion is for steering. Parent may have meant "ring and pinion" which would refer to the differential gear ratio.

Re: Tesla Roadster

#490

Post by Siecje »

in3d wrote: post #365
ardit33 wrote: post #17

The Tesla roadster specs are insane! No exotic carmaker will be able to match it (taking price as a consideration). (no Ferrari, or Lambo, can get that close. This is Formula 1 acceleration speeds). Plus 620 miles of range, and it is a 4 seater. Expensive as hell, but this is exotic car territory. Base Specs Acceleration 0-60 mph1.9 sec Acceleration 0-100 mph4.2 sec Acceleration 1/4 mile8.8 sec Top SpeedOver 250 mph…

Sounds really good on paper but the production is scheduled for 2020, so it’s unfair to compare it to the cars currently on the market. No other manufacturers announce cars so far ahead so it seems at least partly like a hype for Tesla investors. Acceleration is just one part of what makes a great sports car. And how is the acceleration past 100 mph? That’s the traditional weakness of electric cars and it matters mor…

> And how is the acceleration past 100 mph?

I thought the instant torque was able to get great acceleration at all speeds?

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