Thoughts on the new Roadster’s “over 250mph” top speed claim by Elon

[ggnykk]

You need over 1000 horsepower to reach 250 mph, which means all 3 motors are going to have to be contributing meaningfully from launch till top speed. Likewise, you're not delivering over 7000 ft lbs of torque without all 3. If there's no transmission, then they've got to have a pretty wide rpm range.

At least 1100 hp for sure. Remember that NONE of the current cars from Ferrari, Lambo, Porsche, Mclaren goes above 218 mph real world top speed. 250 mph for the new roadster is an INSANE performance for a $200k car.

 

[ggnykk]

What can the average person handle in g's? There must be a point where blackouts might occur.

according to NASA, black out would occur above 3g if special breathing technique isn't applied. Production car or even one-time dragster has a long way to go to reach 3g.

 

[oktane]

How many points on my license if cop clocks me at 250+ mph?

Ethical dilemma, would you pull over or just step on the gas until the flashing lights disappear?

And does anyone else see those signs stating “patrolled by aircraft” as an open invitation to hit max speed?

 

[mongo]

How many points on my license if cop clocks me at 250+ mph?

Ethical dilemma, would you pull over or just step on the gas until the flashing lights disappear?

Good news: radar tops out at 199 MPH usually.
Police Radar FAQ

Bad news: Radio signals travel faster than 250...

 

[TEG]

...Roadster fans know that way back in 2008 the Roadster debuted with a 2-speed Borg Warner gearbox but locked in first gear because the the gearbox kept breaking under hard acceleration...

Actually I think it was "locked" in 2nd gear... slower 0-60 but same top speed.
Those all got replaced, so it was only the very early cars that had them for a short while until Tesla did the promised replacement to 1 ratio but with more torquey motor/PEM.

 

[croman]

How many points on my license if cop clocks me at 250+ mph?

Ethical dilemma, would you pull over or just step on the gas until the flashing lights disappear?

And does anyone else see those signs stating “patrolled by aircraft” as an open invitation to hit max speed?

I'm part of the EV patrol. I'm citing you for using "gas" to refer to an EV's accelerator. Go Pedal is acceptable. Clean up your act and move along.

 

[R.S]

One thing to keep in mind is the total torque output of the three motors. At a claimed 10,000 Nm (~7376 lb-ft). This is more than an order of magnitude higher than the torque output of a high performance ICE, and allows for a very aggressive reduction ratio on the gearset. I'll have to do some calculations to figure out optimum reduction ratio, but it is entirely conceivable that a single gear will be sufficient to produce the ~1.5g of peak acceleration that this car will sustain at low speeds while still achieving a top speed around 250 mph.

This is torque at the wheel. If they have a grating ratio of, let's say 9.73, like the Model S, then motor torque is "only" 1027 Nm, which is still incredible. Other than that the real amount of torque at the motor is totally irrelevant, since you don't know up to which rpm. A super high revving motor with less torque would still be impressive.

Would be interesting to know how much power it can produce.

 

[FlatSix911]

Also, at least one battery researcher thinks the performance figures are feasable:
https://jalopnik.com/heres-what-a-battery-researcher-told-us-about-the-tesla-1820558723

...the fact that the Roadster’s pack is double the size of the one in the Tesla Model S P100D (which is no slouch, making a combined 760 horsepower) 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].

 

[Krazaak]

This is torque at the wheel. If they have a grating ratio of, let's say 9.73, like the Model S, then motor torque is "only" 1027 Nm, which is still incredible. Other than that the real amount of torque at the motor is totally irrelevant, since you don't know up to which rpm. A super high revving motor with less torque would still be impressive.

Would be interesting to know how much power it can produce.

With that ratio and tires around 315/30R20, you're looking at over 30,600 RPM to hit 250. Not outside the realm of smaller electric motors, but given how much more power they have to produce to reach 250 MPH, I can't imagine motors larger than in the Model S hitting almost twice the RPM.

Obviously a guess on the tire size.

 

[Krazaak]

...the fact that the Roadster’s pack is double the size of the one in the Tesla Model S P100D (which is no slouch, making a combined 760 horsepower) 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].

Oh, there's no question in my mind that the 200 kWh pack is there for peak power draw. The 620 mile range is purely a convenient side effect of the power needs. Twice the battery also means the potential for twice the charge rate assuming sufficient cooling.

 

[Cosmacelf]

I blacked out when I saw the price.

. Me too! I was expecting the car to cost so much more! I recovered quickly though and made my reservation.

Back to reality, the P100D acceleration makes me feel woozy. I don’t think I’ll be doing too many launches in the Roadster myself. I’m drooling over the cornering and handling and adequate accerlation.

 

[Cosmacelf]

In another thread, a poster has detailed analysis of how the top speed and acceleration can be achieved.

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

 

[R.S]

With that ratio and tires around 315/30R20, you're looking at over 30,600 RPM to hit 250. Not outside the realm of smaller electric motors, but given how much more power they have to produce to reach 250 MPH, I can't imagine motors larger than in the Model S hitting almost twice the RPM.

Obviously a guess on the tire size.

Well, you can make them rather long, compared to tall. So that the radial forces are smaller. But I still think they solved this with a second gear. If you want a high top speed you want peak power at that point. So letting it run close to the rev limit would be a waste, IMO.

 

[Krazaak]

Well, you can make them rather long, compared to tall. So that the radial forces are smaller. But I still think they solved this with a second gear. If you want a high top speed you want peak power at that point. So letting it run close to the rev limit would be a waste, IMO.

I agree, a 2 speed transmission makes sense unless they've come up with a completely redesigned motor.

 

[rajram]

Let's clarify some metrics by making a quick benchmark using known stats from the Model S P100D. As can be seen from the table below, the combined torque output of the P100D is 791 lb-ft. This is the peak torque output of the two motors. Using the peak power output of each motor, one can then determine exactly at what RPM each motor provides peak torque (shown in the table). Since they each peak at slightly different RPMs, the net torque is a bit lower than the sum of the two, but they do occur at the same vehicle speed (also shown in the table). Likewise, the combined peak power output is lower than the sum of the two individual outputs, but enough to generate 1.37g of peak acceleration (this calculation agrees well with MT's empirical data) while achieving a 155 MPH top speed.

Now, fast forward (no pun intended) to the new Roadster and we have nearly an order of magnitude leap in the combined motor torque output (7377 lb-ft vs. 791 lb-ft). This necessitates much taller gear ratios than the P100D's which allows the three motors to spin at much lower RPMs while still producing massive forces at each wheel. I'm running through some preliminary horsepower estimates and will report back shortly, but rest assured the Roadster is a game changer in every way.

 

[Krazaak]

Let's clarify some metrics by making a quick benchmark using known stats from the Model S P100D. As can be seen from the table below, the combined torque output of the P100D is 791 lb-ft. This is the peak torque output of the two motors. Using the peak power output of each motor, one can then determine exactly at what RPM each motor provides peak torque (shown in the table). Since they each peak at slightly different RPMs, the net torque is a bit lower than the sum of the two, but they do occur at the same vehicle speed (also shown in the table). Likewise, the combined peak power output is lower than the sum of the two individual outputs, but enough to generate 1.37g of peak acceleration (this calculation agrees well with MT's empirical data) while achieving a 155 MPH top speed.

View attachment 261357

Now, fast forward (no pun intended) to the new Roadster and we have nearly an order of magnitude leap in the combined motor torque output (7377 lb-ft vs. 791 lb-ft). This necessitates much taller gear ratios than the P100D's which allows the three motors to spin at much lower RPMs while still producing massive forces at each wheel. I'm running through some preliminary horsepower estimates and will report back shortly, but rest assured the Roadster is a game changer in every way.

I'm pretty sure the torque in your chart is at the motor, vs. torque at the wheels in the published Roadster stats.

 

[scaesare]

How many points on my license if cop clocks me at 250+ mph?

Ethical dilemma, would you pull over or just step on the gas until the flashing lights disappear?

And does anyone else see those signs stating “patrolled by aircraft” as an open invitation to hit max speed?

Can't outrun the ol' Motorola...

 

[R.S]

Let's clarify some metrics by making a quick benchmark using known stats from the Model S P100D. As can be seen from the table below, the combined torque output of the P100D is 791 lb-ft. This is the peak torque output of the two motors. Using the peak power output of each motor, one can then determine exactly at what RPM each motor provides peak torque (shown in the table). Since they each peak at slightly different RPMs, the net torque is a bit lower than the sum of the two, but they do occur at the same vehicle speed (also shown in the table). Likewise, the combined peak power output is lower than the sum of the two individual outputs, but enough to generate 1.37g of peak acceleration (this calculation agrees well with MT's empirical data) while achieving a 155 MPH top speed.

View attachment 261357

Now, fast forward (no pun intended) to the new Roadster and we have nearly an order of magnitude leap in the combined motor torque output (7377 lb-ft vs. 791 lb-ft). This necessitates much taller gear ratios than the P100D's which allows the three motors to spin at much lower RPMs while still producing massive forces at each wheel. I'm running through some preliminary horsepower estimates and will report back shortly, but rest assured the Roadster is a game changer in every way.

Wheel torque! Tesla quoted wheel torque of the Roadster. P100D wheel torque is about 7000 Nm.

 

[rajram]

Wheel torque! Tesla quoted wheel torque of the Roadster. P100D wheel torque is about 7000 Nm.

I'm not aware of any manufacturers quoting wheel torque (or wheel HP, for that matter). By that token, the P100D powertrain already makes a combined output around 10,000 Nm!

 

[e-FTW]

I think they focused on high speed performance, as a smaller and lighter car can probably hit 1.9 with P100D levels of available power. All of the extra power beyond that must be designed for the higher speeds. So, taller gearing than the S, different rations between front and back (like the S, but maybe not as wide of a difference) plus a giant pack that can sustain massive power output for high speeds.
This will be nuts!

Yep. About 10% more torque than P100D gets you this 1.9 seconds to 60.
Ralph on Twitter
That is “all” you need for the acceleration. Everything else (pack size) is there for high speeds.