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

Discussion in 'Roadster 2022' started by ecarfan, Nov 17, 2017.

  1. e-FTW

    e-FTW New electron smell

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    Right on. Although it will not prevent the headlines we've come accustomed to: “Autopilot blamed...”
     
  2. CarlK

    CarlK Active Member

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    The top speed is for bragging rights only although that is important for some. Of all those Bugatti Veyron been sold probably only a handful of them that have ever been driven even once at close to top speed.

    As for a second gear the car probably comes with a second gear only. With such enormous torque there is no need for the low gear.
     
  3. Pezpunk

    Pezpunk Active Member

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    #63 Pezpunk, Nov 27, 2017
    Last edited: Nov 27, 2017
    Correct. Sitting down abruptly can subject the body to 25+ G's ... this causes no harm whatsoever, because it's only for an instant.

    The physiological effects of G forces are extremely dependent on the length of time the forces are sustained. The effects are also strongly dependent on which direction the forces are applied in relation to the body.

    For example, a healthy human body in a seated position can sustain up to around 3 G's downwards (that is, away from the head, towards the feet) without much impact. Forces in this direction in excess of 4 G's or so will cause the blood to be pulled downwards out of the head and towards the feet. This results in blotchy vision (known as a "grey out"), but mental faculties aren't impaired, and vision returns to normal as soon as the forces stop. You can experience this on particularly forceful roller coasters, such as Intimidator 305 at Kings Dominion, which has a huge 270 degree turn at the bottom of its 305 foot first hill. Most riders experience blotchy vision towards the end of this turn (the effect is disconcerting but harmless).

    fba4e8f51bd3310dba71a4657684ab5b.jpg

    As intensity or duration increases, loss of consciousness can occur.

    Meanwhile, "negative" G forces (defined as forces upwards, towards the brain) can be very dangerous. Sustained negative G forces of more than 2 Gs result in burst blood vessels in the eyes, and at 3 G's you start to get brain aneurysms and swelling and bursting, and frankly nobody wants to clean up after that, so the tests usually stop there.

    Interestingly, and more to the point at hand, the human body is excellent at withstanding G forces that are applied perpendicular to the spine, like in an automobile moving forward. So if we are talking about Roadster Mark 2 acceleration, there is practically no limit. Studies show a healthy human body can withstand 20 G's of forward acceleration for a ten second burst, or 10 G's for 1 minute, or 6 G's for 10 minutes.

    I think it is safe to say no automobile will ever come close to eclipsing any of those numbers.

    I mean ... if you were to accelerate at 20 G's for a short ten second burst ... I hope you found a nice long straight-away, because that would put you 6 miles from your starting position in those ten seconds. By the way, you'll probably want to let off the accelerator at that point, since you'd be travelling well over 4000 mph. (anyone want to take a crack at calculating how much energy the regenerative brakes could pump into the battery by decelerating from that speed?)

    Just for funsies ... if you were to get in Tesla Roadster Mark 5, and accelerate at 6 G's for 10 minutes straight, you would eventually reach a speed of about 79,000 mph and travel 6,576 miles in that time. The good news is finding a straight length of road is no longer an issue, since at that point you'd be travelling more than three times the speed necessary to escape Earth's gravity well.

    So yeah. In conclusion ... G forces are not an issue.
     
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  4. Olle

    Olle Member

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    If you take a drag equation D=CD*A*r*V²/2 assume the Roadster has a .36Cd and is 2 m wide and 1.2 m tall you get a drag force of [​IMG]
    Multiply the force with the speed 6533N x 111 m/s=726 kW. Add rolling resistance to this
     
  5. mongo

    mongo Well-Known Member

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    May be a little high there, Original Roadster and semi have Cd of 0.36. Roaster 3.0 was 0.31. Model S is 0.24.
     
  6. deonb

    deonb Active Member

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    Funny, when I first started driving (in South Africa), 100mph was my daily commute.

    Went back a few years ago and got pulled over doing 130mph. Showed them a U.S. drivers license and talked in an American-ish accent and they just let me go: "Welcome to South Africa!". Wasn't going to tell them I was born there...
     
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  7. Olle

    Olle Member

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    High compared to these Tesla cars, but I figured we needed to add some drag for downforce, like the Chiron, which has .38.

    Or otherwise make it super streamlined and add multi directional rocket engines for lateral acceleration (including turning and braking) :)
     
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  8. mongo

    mongo Well-Known Member

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    I can dig it. Gonna need to remember that when doing the tire resistance calculation.

    Does drag due to negative lift increase by the square of speed? Only a certain amount is needed...
     
  9. shokunin

    shokunin P85 & M3

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    They just need to add some deployable grid fins like they use on Falcon 9 for re-entry.
     
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  10. ecarfan

    ecarfan Well-Known Member

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    ”Roadster 3.0”? What Roadster model/version are you referring to?
     
  11. mongo

    mongo Well-Known Member

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    Upgrade package for original Roadster
    Roadster 3.0
     
  12. TEG

    TEG Teslafanatic

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    Yeah, I thought that is what Mongo was talking about. Problem is they never released those aero mods to get it down to 0.31
     
  13. mongo

    mongo Well-Known Member

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    Well that's what I get for copying Google results....:oops:
     
  14. Cloxxki

    Cloxxki Active Member

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    Veyron does 407kph with 1001hp. Roadster could be more slick.
    McLaren F1 in 1992 or so did 387kph or so with 628hp plus some extra revs.
     
  15. Cloxxki

    Cloxxki Active Member

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    #75 Cloxxki, Nov 27, 2017
    Last edited: Nov 27, 2017
    Way too short those straights. Did you see a Model S/X approach top speed? It takes ages. Heavier cars take much longer to get there, and electric motors run out of...torque near ttheir red line.
    Do realize that F1 and LMP1 cars top around 340kph/211mph on such tracks.
     
  16. ecarfan

    ecarfan Well-Known Member

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    Okay. As @TEG noted, the aerodynamic modifications that at one point Tesla stated would be available as part of the 3.0 package were never released.

    So every version of the 2008 to 2012 Roadster had the same CD.
     
  17. Brovane

    Brovane Member

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    The Audi R8 GT has a top speed of over 300+ Km/h. Bugatti is owned by the Volkswagen group and the Veyron and Chiron both have top speeds of over 400+ Km/h. I

    The Tesla Roadster is basically offering "Hypercar" performance seen in the $1M+ cars like a Veyron or a Enzo for low end Supercar prices of $250k. I can totally see Musk telling his engineers this new Roadster has to exceed the performance figures for his old McClaren F1 which had a top speed of 240 mph.

    For those that think that these types of speed are not possible on Public Roads, here is a Bugatti Veyron Super Sport hitting 246 MPH at Sun Valley on a closed off public road. Yes it did make a sound like a low flying jet.



    This type of car like the Veyron for Volkswagen creates a "Halo" car. A vehicle that shows what the company is capable of.

    Yeah a top speed of 250+ MPH is totally excessive but these types of cars are all about being excessive.

     
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  18. HankLloydRight

    HankLloydRight No Roads

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    Thanks for such a fun-to-read post! Very interesting stats.

    I rode Millennium Force at Cedar Point about 4 or 5 times in a row one day. On the last run, at the bottom of the big hill and the top of the following hill, I almost blacked out -- really couldn't see anything for (what seemed like) several seconds. That's when I decided it was time to call it quits and go home. :)
     
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  19. J X 3

    J X 3 Member

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    I think you guys are focusing on the wrong speed, no production car hits 300mph and doing that would have the biggest marketing impact.

    Rolling resistance (including downforce) is small and you don't want downforce at peak speed to waste HP.
    So it's about drag and that energy=1/2 x air density so 1.225 x v^3 x Cd x frontal area
    v= 134,17 m/s
    Cd is gonna be better than ICE competitors, for one they don't focus much on downforce and , more importantly,, it seems that because of the huge battery, they don't need huge air intakes - this is a big problem with ICE as it adds drag and it is very problematic with EVs too but it appears that the huge battery helps a lot here- we don't know what kind of air intakes they have under the car.
    So let's say Cd=0.3 but could be even better
    Frontal area haven't tried to measure but let's say 2m
    These numbers get us to 0.8875MW and a horsepower is 745.7W so we need 1190.2 HP. Rolling resistance might add 50HP or something depending on tires and downforce and there are some losses from motor to road but if they got anything close to 1500HP it should be enough.

    Now if they have Cd=0.25 and frontal area at 1.8m, it gets much easier. They would need 893HP + rolling resistance+ losses but it's doable with under 1200HP.
    For how long they can cool those motors without bigger air intakes, I got no idea but this car can end up being the first production car to hit 300mps (483km/h).
     
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  20. oneday

    oneday Active Member

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    This post aged well. Clairvoyant, really.
     
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