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Tesla Semi gunning it from a standstill

Discussion in 'Semi' started by e-FTW, Nov 25, 2017.

  1. e-FTW

    e-FTW New electron smell

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    Cab only. Traction limited of course, very impressive to see it go like that though.
     
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  2. EVSteve

    EVSteve 110% Solar Powered

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    As a trucker yes that is absolutely traction limited. Bobtail in a Class 8 there's very little grip. Looks like they mounted super singles on the drive axles too which only makes the traction problem worse. I'd like to see these accelerations with a pup trailer weighed down at the nose with maybe 10,000 lbs in the box
     
  3. jkn

    jkn Member

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    EV has enough torque so acceleration is limited by traction! For example accelerating 80 000 lbs with 700 kW at 14 mph gives 0.31 g
    P=F*v=m*a*v <=> a = P/m/v
    700 kW / 80000 lbs / 14 mph = 3.0822502 m / s^2 = 0.31 g

    Does it have traction for more? I guess no. So acceleration is traction limited to 14 mph (2.03 s).

    Acceleration continues with constant 700 kW:
    Energy needed is 0.5*80000 lbs *(60^2 - 14^2) mph^2 = 12.34 MJ
    12.34 MJ / 700 kW = 17.63 s -> Total acceleration time 19.66 s

    700 kW is very close to correct power.
     
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  4. ahaer

    ahaer Member

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    don't forget 800-1000kWh of battery weight (8000lbs???) over the rear wheels to help with traction...
     
  5. EVSteve

    EVSteve 110% Solar Powered

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    Tesla said the difference in powertrain specs puts the semi in the same weight range when compared to a conventional ICE tractor. On those tires with no weight over the rear there is zero grip. Most of the weight on semi truck cabs is over the front tires to make weight capacity available for what's in the trailer. Government DOT regulations limit the max poundage on the drive tires to be 34,000 lbs loaded. The weight is up front by design on purpose.
     
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  6. Brando

    Brando Active Member

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    ",,, wide single tires (wide single tires replace the double tire on each end of a drive or trailer axle, in effect turning an 18-wheeler into a 10-wheeler)."

    "Our fuel-efficient truck tires offer low rolling resistance and can be used with lower-weight aluminum wheels to further improve fuel savings. Expect decreased emissions, improved fuel savings and a brighter future for our planet."

    Smartway Tires | Michelin Truck

    PS- Tesla SEMI truck has traction control and doesn't depend on weight for traction.
    New Roadster seems to generate almost 1.2 Gs up to ~70 mph before traction controls stop limiting wheel spin.
     
  7. EVSteve

    EVSteve 110% Solar Powered

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    Ok? Traction control only makes more efficient use of available traction. The amount of traction available doesn’t change just because a computer is actively managing slip.

    If weight had no effect on traction why do oversized load haulers add weights to the drive wheels of multi tractor configurations? Why if I have no trailer do I have less grip in rain or snow? Weight matters.

    The roadster still has an even weight distribution across the four tires and all wheel drive. Completely different setup.
     
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