I've noticed that the range calculator is back, now imbedded in the specs page on Tesla website. The odd thing is that as one changes outside temp with "heat on" all versions increase range as outside temp increases until it reaches 70ºF, when the "D" version ranges continue to rise but 85 drops slightly. Same thing occurs at 90ºF outside temp. At 110ºF outside temp all versions' ranges decrease.
I've not yet heard back from Tesla via "contact" form, so I will ask here. Odd quirk of the single motor version, or website design error?
My thoughts:
Side Info:
First, just as important as the air temperature is the cloud coverage, because you're driving around a big greenhouse. With a 90 degree cloudy day, you'll use much less air conditioning on a typical drive than a 70 degree sunny day...but I digress. (Point is, Tesla ought to have a setting for cloud coverage in the calcualtor).
Let's look at what the effects are of increasing air temperature:
1. Air density decreases. At higher speeds, drag is the largest factor in energy loss, so this component contributes to an increase in range in all models. It's unaffected by RWD vs. AWD.
2. WRT climate control, heat uses more energy than air conditioning. At colder temperatures, this results in a significant loss in range. Around 70 degrees, it's minimal. At higher temperatures, it rises again, but not as significantly as the loss of range due to heat. This effect is technically not dependent on RWD vs. AWD, however you'll notice that with climate control off, the 85 range increases continuously as well.
3. Because of (1), the ability of the air to cool the heat exchanger is reduced. Moreover, the temperature of that air is higher. Since the amount of heat extracted by airflow over the heat exchangers is dependent on the difference in temperature between the air and the warm heat exchanger, this reduces heat extraction even more.
The answer lies with (2) and (3). When cruising on the highway at a given speed--whether it be a RWD or AWD vehicle, you're consuming a continuous amount of power. But it's slightly less with the Ds due to the improved gearing with the dual motor system. An S85 might consume 40 kW at a given speed, and a D might consume 36 kW. The waste heat is roughly proportional to the amount of power produced. With the D models, this power consumption is distributed between the front and rear drive units, whereas with the RWDs it's concentrated in the rear motor.
So suppose just for the sake of argument that 1 kW of waste heat is produced while developing 40 kW of "cruise power" in an RWD S85. Perhaps 800W of waste heat is produced while developing 36kW to cruise in a D. After a short time, this waste heat needs to be eliminated by the cooling system.
With an S85 (RWD), the heat is concentrated in the rear drive unit--and it has slightly more waste heat. Therefore, more cooling is needed. With A/C on, this means some of the cooling air must be diverted to run over the heat exchanger. As a result the compressor/fans must run at a higher level to keep the cabin temperature constant.
With the Ds (AWD), the 800W of waste heat is spread across two drive units. Because there's slightly less waste heat, and because that heat is spread across both motors, less cooling air is needed. Therefore, less air is diverted from the cabin cooling, so the compressor/fans don't need to work as hard to cool the cabin.
There's probably also some effect in that the louvers that take in outside air for the heat exchanger don't need to open as much, therefore body drag is reduced as well.
That's my take on it--seems like a reasonable explanation.
