You're severely underestimating wheel torque. We know the car produces well over 1G. See post #34.
*just convert horizontal force (g) to rotational force (ft/lbs). Simple.
No I'm not, read *all* of what I wrote. I clearly stated "This represents the *average* torque, the peak torque would be much higher." I did not state a value for "much higher" because I thought that it should be quite obvious that achieving 1.14G of acceleration in a 5,000 pound vehicle with 1.12 foot radius tires would require a peak torque of 5,600 pound-feet, and it does not need to sustain that value for very long since the average is "only" 3,340 pound-feet. I also wanted to point out that the 920 pound-feet torque value was computed (with gearing ratio and gearing loss assumptions) and not measured since the wheel torque and RPM were the only things being measured on the dyno.
And since I am here, we could estimate the motor torque in the following way.
A recent ARS Technica article (
Tesla’s P100D: I got 99 problems, but not being able to go really fast ain’t one) claims: "That's 259hp (193kW) at the front, 503hp (375kW) at the rear—although the maximum combined power output is 680hp (507kW)."
Taking the ratios of the motor HP values (the motor torque ratios would be better, but we don't have those numbers) we get that the rear motor provides about 2/3rds of the total power (the front motor is rated at 51% of the rear motor, HP wise). Since the rear motor gearbox has a 9.73 ratio and it provides about 2/3rds of the torque, while the front motor gearbox has a 9.34 ratio and provides about 1/3rd of the torque, we can estimate that the equivalent single motor and gear box has about a 9.61 ratio and the resulting lossless motor peak torque would be 583 pound-feet. Straight cut involute gears can have a typical loss of 2% per meshing pair, but Tesla uses helical gearing for quieter operation and greater strength. If we assume a 5% loss for the single helical gearing reduction (and it is likely not that high since helical gears can generally approach straight cut gearing losses), that results in 612 pound-feet of torque, or right at 2/3rds of the claimed 920 pound-feet.
Lets approach this from another direction, using the same equivalent gearbox ratio and estimated gearing loss, but starting with the claimed 920 pound-feet of motor torque. That torque though a 95% efficiency 9.61 ratio gearbox results in a total peak of 8,400 pound-feet at the wheels. If that amount of torque was transmitted to the dyno the peak acceleration would be 1.5Gs. I am unaware of any published measured P100D accelerations reaching above 1.2Gs. Also note that the torque plot shows signs of obvious wheel slippage from about 40 to 48 MPH, and as a result the available peak torque was never actually reached on that dyno.
From the above it is apparent that the claimed 920 pound-feet of peak Tesla P100D electric motor torque based on the provided dyno measurements is completely bogus. The dyno people obviously blew the computations for equivalent motor torque. The HP number should be more accurate, depending on what they assumed for the gearbox losses. Measuring the torque and RPM at the wheels does allow for an accurate wheel HP computation.
