Actually, different Model S have different rated Wh/mile. My Model S 60 was 287 Wh/mile (IIRC), the P85D is 304 from what I can tell.
What Size tires on your model xI finally was able to make a "normal" trip. Tires broken in, weather mild, elevation changes minor and urban freeway speeds 60 to 70 mph on first leg and slower return, in heavy traffic at 45 to 65 mph. Here are the charts.
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The trip B total miles are almost all higher speed (75 to 85 mph) and low temp miles. The trip A was today's 90 mile normal urban round trip. Mostly freeway but not high speeds.
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Energy chart with rated miles line displayed. This segment was rush hour freeway with lower speeds (40 to 50 mph).
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I drive pretty normal and dont worry much about trying to get better Wh/mi numbers. I just drive and don't use the brakes very much. No effort to maximize efficiency.
Mx75d : about 900 miles on the car in Connecticut (winter months) averaging 400-425wh/m ... much higher than my MS : which was about 320-330 with 34k miles lifetime.
Short trips in winter weather always give ugly results, as you're probably aware. Here's my five month old X75D:
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And even that 335 Wh/mile number is driven up by far too many miles at 75 in freezing weather on my 4k+ of road trips since late October and a lot of winter commutes.
(I've recently started turning range mode on for the commute when it isn't precipitating - my ten miles aren't enough to get the battery warm anyway, so why waste power trying? The result is a 10-15% drop in energy usage, as you see here - 46 degrees, maybe a third of the drive at 75+.)