Max power at high speeds

[SSedan]

The Tesla should always be slower given the HP to weight ratio. So why be surprised the ICE finally gets it's act together and accelerates faster? At the strip a higher trap speed with equal time means you have a better hp to weight ratio and you need to work on the launch.

BTW I can verify the P100D is not "soft up top".

My point was how little time an ICE actually spends at peak tq/hp compared to electrics, and that with a P85 after 73mph it is constantly making less power where an ICE can get to the next gear and get back up to peak power again. A P100D is just such a big hammer you don't notice it.

 

[AmpedRealtor]

If we had another gear or two, the highway performance would be amazing . My guess is the roadster will have two or more gears .

I hope that thought isn't giving Tesla engineers shivers given the gearing issues they had with the original Roadster.

 

[Krash]

Interesting that with multiple induction motors you could freewheel one while you change gears, unlike ICE models where there is one engine and one transmission and a gap while anything other than a CVT changes gears.

I know we have different gear ratios on the two AWD motors today. I wonder if you could temporarily load increase one drive while the other changes gears to prevent a lurch as drives come off and online.

 

[The Duke]

Interesting that with multiple induction motors you could freewheel one while you change gears, unlike ICE models where there is one engine and one transmission and a gap while anything other than a CVT changes gears.

I know we have different gear ratios on the two AWD motors today. I wonder if you could temporarily load increase one drive while the other changes gears to prevent a lurch as drives come off and online.

I am sure you could, but why? Added complexity, weight and decrease efficiency for performance over 80 MPH with smaller battery packs and motors?

 

[n2mb_racing]

I am sure you could, but why? Added complexity, weight and decrease efficiency for performance over 80 MPH with smaller battery packs and motors?

I just don't know how else they would reach 250 mph, while delivering 0-60 times of 1.9 seconds without adding at least one more gear. The two specs are pretty incompatible without changing gearing at least once.

 

[mongo]

I just don't know how else they would reach 250 mph, while delivering 0-60 times of 1.9 seconds without adding at least one more gear. The two specs are pretty incompatible without changing gearing at least once.

Not incompatible
Low speed acceleration is based on torque which is based on current limit
High end speed is limited by:

• Max motor RPM
• Motor Back EMF
• Pack Voltage
• Force needed

To hold a speed, the car needs to put out as much power as there is drag+friction+drivetrain loss.
The output power is (Pack voltage - BackEMF)/MotorReistance * PackVoltage (for 100% duty, add in your own motor factor for accuracy).
Factoring in max motor RPM, if the gearing needs to double for the 250 MPH number, then that divides the motor to road torque by 2 and the backEMF vs road speed by half.

With a 200kWh pack, the pack can likely do at least 2x the current of the present top dog top dog. This then goes to twice as many rear motors. Each motor only has half the available load (one loaded tire vs two). So each motor can only put out half the power/ torque of the 100DL before wheel spin kicks in. With the modified gearing, that puts the motor right back where it started. So, each motor produces the same shaft torque at the same current level as a P100DL yielding the same total rear wheel torque.

At the high end, there is double the power available due to dual motors. By reducing frontal cross section and coefficient of drag, that gets most of the way to the needed 4x power for 2x speed increase. Plus there is the gain of PM vs AC induction motor.
They could also use a higher voltage pack to increase top end (less likely due to part reuse)
Last knob to turn is trading torque per Amp (low end) for V/RPM (high end) by using a different motor winding.