Range speculation

[malcolm]

It seems like a good time for a new one of these: Range Speculation

Now that we have this:



Do we have any thoughts on how the contributing elements will shift for Model S? E.g doubling the Tire value to 100 Wh/mile???

Can the Excel worksheet be modified to help with this?

[graham]

I am betting the Model S pays more attention to aerodynamics than the Roadster.

It will definitely be much heavier. Would that make the tire value go up, as you are speculating malcolm?

And I assume the drivetrain will be roughly the same.

[WarpedOne]

Model S is a bigger car with bigger frontal area than Roadster. This is a major factor in wind resistance. A car with 10sqft frontal area having 0.4 (very high) drag coeficient has lower overall drag than a car with 20sqft frontal area and 0.25 (very low) drag coeficient. Aerodynamics has its limitations.

It is also heavier (I'd guess around 4000 pounds) meaning it's tyres will have higer rolling resistance (25%?). Acceleration will eat up more energy than it does with the Roadster.

There is one upside though. Model S doesn't need to go as fast. If it was limited to say 105 mph, the motor would have higher average rpm and thus higher average efficiency.

There are still many oportunities to decrease ancillary loads like that little water pump, 100W headlights, combining heater with ESS cooler, etc but all this together cannot improve EPA range by more than 10%.

Model S will need to have higher capacity ESS just to match roadster's EPA range.
This should be doable by using somewhat higher capacity cells. No need to go for top of the line, 2Ah to 2,5Ah (52kWh to 65kWh) is already a 25% improvment that might be enough for 250 miles EPA range.

[malcolm]

Would that make the tire value go up, as you are speculating malcolm?

Yes, but the value of 100 is a complete guess.

[raymond]

There is one upside though. Model S doesn't need to go as fast. If it was limited to say 105 mph, the motor would have higher average rpm and thus higher average efficiency.

I thought I was quite up to speed with the theory side of things, and I wouldn't expect higher average rpm to translate to higher efficiency.

I'd think higher rpm gives higher friction and such.

In general, electric motors work at higher average efficiency as they work nearer their peak power. But since the EPA highway cycle typically runs at perhaps 15-20kW this doesn't seem important for the roadster or the model-S.

WarpedOne, can you please expand on the higher rpm -> higher efficiency?

[WarpedOne]

Higher rpm of an AC motor means higher frequency and lower amperage for given constant power. Lower amperage means lower heat losses. Lower heat losses mean better efficiency.

Of course there are diminishing returns, but as long as average speed is less than half the top speed, the increase in average rpm means increase in average efficiency.