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If Model S had a CVT

Discussion in 'Model S: Driving Dynamics' started by Beckler, Jul 19, 2015.

  1. Beckler

    Beckler Member

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    I wonder if anyone has done the calculations for acceleration, top speed, etc. if a 762-hp P90D were to have a CVT.
     
  2. Fezzik

    Fezzik P67429

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    I bet it would tear the belt in the cvt up. All that torque at once. I mean the p85d breaks belts on dynos
     
  3. mgboyes

    mgboyes Member

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    This.

    No way you could get anywhere near to the initial torque delivery of the current car through a CVT gearbox. And top speed is mostly a function of maximum continuous power output - no gearbox can help with that.
     
  4. Beckler

    Beckler Member

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    But let's just assume a CVT can be done. But go ahead and assume a 5 speed gearbox or whatever; who cares. Regardless, a higher gear ratio would have to give a higher speed than 155 mph given the 762 hp. I realize it couldn't sustain that power continuously and of course I never suggested that.
     
  5. mgboyes

    mgboyes Member

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    Aren't the maximum speeds quoted for vehicles the highest speeds they can sustain continuously? For the Model S I expect it's somewhere around 155mph, and no kind of gearing will change that.

    Also if you want to assume a 5 speed gearbox, why not just assume a different motor, or a bigger pack, or different aerodynamics?

    If your question is "if the only thing that mattered was a higher top speed, could Tesla deliver it?" then the answer is "yes". But that's true of any car company: Lamborghini could make the Aventador have a faster top speed if they wanted to, by sacrificing other things.
     
  6. Beckler

    Beckler Member

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    I think this is just over-complicating things. My only question was does anyone know how much a P90D would theoretically benefit in performance by not being restricted to one gear ratio. The answer is no, apparently. :)
     
  7. dpodoll

    dpodoll Member

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    I bet nobody at Tesla even considered this
     
  8. Zythryn

    Zythryn MS 70D, MX 90D

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    Theoretically performance would suffer as the CVT would break.
    You would also add to cost and maintenance, and weight, slowing it down a bit more.

    I don't understand why people are trying to apply Stone Age technology to rockets. It simply is unnecessary.

    As for increasing performance even more, wait till the Tesla built Roadster in 2019. It should embarrass the remaining super cars that haven't already been embarrassed.
     
  9. WarpedOne

    WarpedOne Supreme Premier

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    They've considered it but quickly found that it is not worth it.

    The best CVT is an electric one.
     
  10. Saghost

    Saghost Active Member

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    The available data suggested there would be virtually no benefit, only a slight advantage at higher speeds - and that assumes your notional CVT is as efficient as the current gears in transferring power.

    From 0-30 the current car is traction limited. No amount of additional power can make it move faster unless it is delivered by something besides the tires. The only way to speed it up would be sticker tires or traction compounds on the pavement - or rockets. :D

    Elon's statement said that the P90DL extends this up to close to 60 mph - meaning that no transmission will make the car faster up to that point.

    Above 60 there's a constant power range, which a CVT also won't help.

    Somewhere in the 80-100 mph range, though, the car starts losing power due to back EMF effects. This is the one place your notional perfect CVT could deliver more power - by slowing the motors down, it could reduce the back EMF issues and allow the constant power region to extend up to the maximum speed the car can reach.

    In real life, however, a CVT able to handle the rear motor's torque has never been built to my knowledge. If it did exist, it would be a lot heavier than the existing gears, and lose more power (good CVTs are 90% efficient - the current fixed gearing should be ~98%.)

    That means the car would be slower in normal speed ranges and need more energy per mile, but might have an advantage at >100 mph speeds.

    OTOH, they could get a very similar result without the extra weight by gearing the motors taller - except it would be more efficient, requiring less energy per mile.

    A car biased for high speeds might justify a two speed transmission, though that means more weight and cost and complexity, more things to fail.
    Walter
     

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