I am not sure the decreasing acceleration isn't just a function of increasing aerodynamic drag. Power available to accelerate the vehicle decreases with velocity in a non-linear, polynomialistic fashion. That's right, I just made that term up! I am also curious when the motor torque starts to fall off, I just don't know if we can conclude it yet...
Yes and no.
This is where the link between torque and power get confusing.
that graph is somewhat misleading because it's mixing units, if you re-label the bottom axes with motor RPM, then you would have a classic power/torque graph, although it should look more like this:
Not the lack of 'step' on the falling torque curve after base speed.
(this graph is a typical perm mag motor without any software torque shaping)
Now, back to first principles, torque is a factor of voltage applied to the motor, the higher the voltage, the more torque.
as you go up the rev range, the current (amps) to the inverter needs to rise as the frequency rises - voltage to the motor remains the same.
Once you get to the current limit of the inverter (or motor) then you are at the point in the graph labeled "base speed".
After this, assuming you maintain the current level, the voltage to the motor will start to drop and thus the motors torque, the power curve will basically go flat at this point as you have reached the maximum power for the system (in reality, at higher revs, the power will drop off marginally as the changes in motor/inverter efficiency take effect, but assuming a well designed system, this is not that significant).
Back to the 3, from what we have seen (if the numbers are to be believed), the base speed for the 3 is either ~3,832Rpm (Max power 165KW or ~4,700Rpm (202KW) - all assuming the torque figure given (3,700Nm / 9 = 411.11Nm = 303.22Lbft) are correct.
Then we get to acceleration - F=MA
combined with aero drag -
and finally, rolling resistance -
Fr = c W
The first we can work with, the second & third requires the Aero/coefficient of rolling friction figures for the 3 (anybody got figures for the 3?)