Engineering Analysis: Tesla Roadster Performance Specs Validated

Tesla Roadster

MAR 29 2018 BY GEORGE BOWER 35

We validate the upcoming, second-gen Tesla Roadster performance specs and also share some other interesting tidbits.

When the performance specs for the Tesla Roadster were announced there was lots of skepticism and many questions. Is there some new magic battery chemistry required for the Roadster?

Related: Tesla Roadster Torque Questioned

A few publications took a stab at answering the questions. Electrek had an excellent article on it. Here’s what Fred said in that article:

First thing’s first, let’s talk about the go-fast stuff.  With Tesla’s stated specs, and with that huge battery, this car must have a lot of power.  The 200kWh battery isn’t just there for range, it’s for power.

Jalopnik reached out to a Carnegie Mellon professor and here’s what he said:

To learn more about how the Roadster could reach rally car-like acceleration figures, I spoke with Carnegie Mellon’s Venkat Viswanathan, a mechanical engineering assistant professor who works at the Wilton E. Scott Institute for Energy Innovation and focuses on next-generation battery technology.

Viswanathan told me that when it comes to motor output and thus vehicle acceleration, you’re really limited by the power draw from each cell. But the fact that the Roadster’s pack is double the size of the one in the Tesla Model S P100D means that the power pulled from each cell won’t be as crazy as we think. Viswanathan told me over the phone that, “the power draw may not be that much more than [the cells in] a ludicrous [Model S].”

My engineering partner Keith Ritter and I decided to build a computer model of the Roadster. The model is quite detailed and includes specifics like detailed motor maps, gear ratios, and even tire sizes. Also, we included published specs for Tesla’s NCA battery chemistry. These specs include maximum power draw for three seconds, 10 seconds, and continuous. If you want to see the specs, head over to Jason Hughes website for HSR motors.

In order to verify the math, we first modeled the P100D, and the model predicted Tesla’s published specs for that car.

We then modeled the Roadster using all available data. We had to calculate new gear ratios since the car can go 250 MPH. Elon has already told us the car has 200 kWh battery and 10,000 Nm of axle torque. We started with motor HP and torque for the P100D, but used two motors on the rear axle and one motor on the front. We then scaled motor torque and HP till we got to the magic 1.9-second 0-60 acceleration time.

Here are the extra tidbits:

What we found is that the Roadster with 200 kWh battery is achievable with existing Tesla NCA battery specs. No magic new chemistry involved, just like the Tesla Semi. We needed every bit of power the 200 kWh battery could put out but we were able to get the performance we needed with the specs published at HSR Motors. In addition, we had to scale up the P100D torque and power levels.

The model predicts:

  • Range= 700 miles+
  • Total axle torque=10,000 Nm
  • Total Hp=1242 HP/926 kW
  • 0-30 time=0.9 seconds
  • 0-60 time=1.8 seconds
  • 0-100 time=3.1 seconds
  • ¼ mile time =8.3 seconds
  • Top speed=250 MPH

The above horsepower falls directly in line with Electrek’s previous estimation:

I’m estimating that power will be in the megawatt range, so around 1,300 horsepower. Give or take.

*Keith Ritter contributed substantially to this analysis.

Sources: Electrek, Jalopnik

Categories: Tesla

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35 Comments on "Engineering Analysis: Tesla Roadster Performance Specs Validated"

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Sladjo

Engineering (off line) analysis is good but we are eager to see real life test results and confirmation(s).

John

8.3 in the quarter mile?? Sheesh…

*And for all you folks who wanna bring up Nurburgring, that’s an ENTIRELY different conversation. One in which the 1/4 and track discussion are completely different.

Tim Kulogo

I’m very excited to see what it can do an Nurburgring. Working backwards from other cars, the new roadster should have between 250 and 350 horsepower of electronic breaking. That would alleviate so much break fade. The roadster also doesn’t reach full power until 80 to 100 miles an hour (higher when cornering), so the battery overheating trouble should be reduced. Add all that to a super low center of gravity and what must be the stickiest of tires, and I think it’ll do just fine.

floydboy

I hope there’s no ‘breaking’ at all! Spoils the fun.

ffbj

Oh, so true. You could give him a brake though.

dinhh68

floydboy & ffbj

nicely done!

pjwood1

I get how “More KWh allows a lower C-rate, versus going with higher C-rate and less KWh”, but that leaves one question.

Weight/Inertia??

I’m convinced a 5,000lb car can still be fun on less technical tracks, but actually going for time with nearly constant brake/acceleration cycles will set a short fuse on heat. I hope Tim Kulogo is right, that 250-300HP regen rates will be possible, but that’s another heat factor where current Tesla owners have to turn regen *down* in the pits.

VW’s Pike’s Peak entry, as much as I dislike them, is most likely to meet a good BEV formula for recreational track use. The uphill is very demanding at ~10+ minute elapsed times, which should translate well for how such a BEV would last for ordinary 20-minute “driver’s ed” sessions. -Note, this could be a one-time VW exhibition because they aren’t genuinely interested in EVs.

Benz

200 kWh battery pack:

Twice as heavy in weight and also twice the volumetric dimensions as the 100 kWh battery pack of the Tesla Model S?

Enlighten me please.

(⌐■_■) Trollnonymous

They took the P100 packs and made a sandwich with it?

Doggydogworld

No way. The Roadster is too low of a car for a double-layer pack. Even their existing S/X packs are too thick.

Robann

The 2170 cell is around 50% larger by volume than the 18650, but it can deliver almost double the current (the 18650 delivers 3,000 mA, and the 2170 has been tested at 5,750-6,000 mA).

https://evannex.com/blogs/news/tesla-s-new-2170-cell-packs-more-power

Pajda

Tesla model 3 cells 21-70 are ~5000mAh, there are also another manufacturers which have 21700 cells in mass production with similar capacity. Rimac concept 2 uses 21700 cells with only 4750mAh capacity (most probably produced by Samsung). No one have 21700 cells with significantly higher capacity than 5000mAh in mass production today.

floydboy

The ridiculous instantaneous torque of cars like these(Tesla Roadster, Rimac C2) could land many a ‘would be’ racer in over their heads rather quickly. I wonder if an ‘always on’ traction control system is warranted. I believe the one in the Model S, has saved many-a-butt from the weeds.

Gasbag

“we included published specs for Tesla’s NCA battery ”

Good to hear they can do it with NCA but what are the ramifications of using NCM-811? Hasn’t Dahn’s Team been focusing on NCM?

Bill Howland
No offense but haven’t seen much analysis here. I could care less about ridiculous torques anyway, since, even with AWD the cars become difficult to drive unless a professional is at the wheel. Absolutely no mention has to been made as to the group of motors’ BASE speeds which is not even mentioned here nor basically at any time ever in INSIDE EV’s, other than my comments. The one link does IMPLY the base speed of the ‘s’ to be from around 40-50 mph, but that’s a different car, whose asynchronous motor has FAR DIFFERENT CHARACTERISTICS than the Synchronous units (Supposedly) used in the new Roadster. Quite amazing there would be so much ‘ analysis ‘ here when there is so little to go on. And of course then not mentioning any details in the article. Reminds me of Col Klink asking what is wrong with his truck this time? Newkirk responds, ‘The technical answer is, it is Broke”. Of course, that show was supposed to be a gag. I think the subject is somewhat overblown anyway. My only concern usually about torque with a Synchronous (permanent) motor is that the peak has to be watched to make sure the… Read more »
Stash

I’d like to know where this vehicle will be manufactured. Fremont? Once the already reduced demand for S, X & 3 forces production rollbacks?

Or, will it be the semi-truck plant that does not yet exist for a vehicle that is supposed to debut next year?

Where will the $$$ for plant construction come from?

Discussing the performance specs of a nonexistent Tesla vehicle at this stage is the equivalent of dreaming about what you’ll spend your future lottery winnings on.

SansIce

Oh – you mean like any of the scores of articles from VW/Audi/Porsche/ ? At least Tesla has built and produced the P100D and Roadster – the others have no proof that anything they say will ever happen.

Tom S

This axle torque number is a joke.

The more they try and push it the cringier it gets.

Aaron

Why? SpaceX and Tesla are joined at the hip. There is no reason why some expensive, high-strength materials wouldn’t be able to handle that amount of torque. Remember, even the Model S uses “space-grade bolts” (SpaceX technology) in its manufacturing process.

Even a Dodge Ram 3500 diesel has 930 ft/lbs of torque, before the transmission reduction is taken into account. A quick search for the manual transmission version shows a little over a 30:1 ratio in first gear, putting the torque numbers at over 27,000 ft/lbs.

Listen alpha 12 gtr can do a quarter mile in 8 to 9 and a half seconds depending on surface conditions and can do o-60 in under 2 seconds or more depending on track surface so all performance numbers are in question for any car. But I will say my point on any car is to be called a sports car you must be able to handle extreme driving conditions. The Porsche gt2 rs with only 700 up went around the nurburgring in 6:47 seconds!!!!
A true sports car tester for all companies to show what their car can do. Any sports car can drive fast in a straight line. I seen a video where a Nissan juke destroyed a veyron but so what, that juke couldn’t even take a corner. Any yuppie can drive fast in a straight line but a real sports car must be track proven. I know 2 civics that can go 2 seconds 0-60 and do 8 seconds quarter miles but that’s it . Performance cars are not sports cars and until proven on the track well talk is cheap.

Bul_gar

What car is bmw i8 then?

Doggydogworld
I disagree completely with this analysis. First, you don’t need 1300 hp to meet these specs. Certainly not for acceleration – The much larger Model S P100D is only 20% slower, so that same 100 kWh/680 hp pack is clearly sufficient to break 2 sesconds in the smaller Roadster. Furthermore, there’s simply no way to get 1300 hp to the pavement in a 0-60 run – you’re limited by traction. 250 mph requires more power, but still not 1300. Lucid Air is much larger and did 235 mph on 1000 hp. Roadster2 road load shouldn’t be more than ~15 kW at 100 kph (62 mph). If that’s 10 kW aero and 5 kW rolling resistance/accessories, scaling to 400 kph (249 mph) gets you about 650 hp. But the real reasons I say Roadster2 does NOT use NCA are common sense: 1. Schedule. They could sell a NCA-based Roadster2 this year. 2021 ship date is driven by availability of the new battery chemistry. 2. Cost. Semi pricing shows Tesla expects NCA/NMC to be < $100/kWh by 2021. The $250k Founder's Series pricing indicates a $500/kWh chemistry. 3. Space. This is a small car, with a low roof. Space is at a… Read more »
Benz

“availability of the new battery chemistry”

How else will Tesla be able to fit a 200 kWh battery pack in the Tesla Roadster?

But they don’t want to reveal anything yet.

Hi there,
you are right, you are traction límited at first but after 120,the car is power limited.
I had done those analysis for a small thesis https://goo.gl/2pnRQt and I can tell, the car would need that power to reach over 400km/h

MicMac

How can you validate something without access to the car?

Bul_gar

For $200k with such battery and power I don’t expect carbon fiber. What will be the specs with lower weight a lot carbon fiber, carbon ceramic breaks and carbon wheels

Mister G

GO TESLA GO DESTROY DIRTY GAS GUZZLERS

Pushmi-Pullyu

“…the Roadster with 200 kWh battery is achievable with existing Tesla NCA battery specs. No magic new chemistry involved, just like the Tesla Semi.”

That’s what I’ve been saying! It’s nice to have some real engineers back up my merely semi-informed guess. (See what I did there? 😉 )

I don’t think Tesla would be investing billions of dollars in current battery tech, at Gigafactory One, if they had access to significantly better battery tech which is going to be available in a year or two.

Pushmi-Pullyu

Trollnonymous asked:

“They took the P100 packs and made a sandwich with it?”

Very probably not. Look at the placement of the battery pack in the Roadster Mk I: It was all in a box behind the seats.

If the floor of the Roadster Mk II (my term, not Tesla’s) is as low as people say, this strongly suggests that Tesla put the batteries elsewhere. I’m guessing two packs, one behind the (rear) seats and a second, possibly smaller pack, under the hood. Not a “skateboard” design at all.

If I’m right, this means the Roadster Mk II will have its own special battery pack(s), not standard Model S/X packs.

Pushmi-Pullyu

Stash said:

“Discussing the performance specs of a nonexistent Tesla vehicle at this stage is the equivalent of dreaming about what you’ll spend your future lottery winnings on.”

It’s not nonexistent. Tesla has already shown the prototype and has given rides in it to quite a few people.

Perhaps you have confused Tesla’s promises with Volkswagen’s vaporware. When Tesla shows a prototype and says they are going to put the vehicle into production, then they do so. Probably later than they originally claimed, but by and by.

Pushmi-Pullyu

Doggydogworld said:

“3. Space. This is a small car, with a low roof. Space is at a premium. 200 kWh of NCA won’t fit.”

Well, a lot of people over on the Tesla Motors Club forum disagree with you.

But from discussion there, it looks like I gave too much credit to misinformed comments about the placement of the battery pack. There seems to be agreement in that discussion that indeed Tesla has double-stacked two 100 kWh battery packs underneath the floorboards of the Roadster Mk II, and that the seats are that high.

https://teslamotorsclub.com/tmc/threads/200-kwh-roadster-pack-how-is-tesla-pulling-this-off.102274/

Doggydogworld

Pushmi – that thread has a lot of silliness.

I have an Elise. A double stack battery would raise the floor higher than my minivan. You’d have to recline >45 degrees to fit under the roof. The whole idea is a joke.

Even a single stack is too high. My guess is a 2″ high pack of solid state or other next gen prismatic cells. Plus another pack on back.

Do not be counted among goats who do wrong things to others. Car manufacturers have to make good and economy cars to satisfy their customers.

jjj

What drag coefficient, frontal area and weight did you guys use? Around 0.25 . 1.8m and 2000kg?

James

Most important question is still unanswered
But how do you fit a 200kWh pack in a sports car?