A couple of things.
First off: No question, Tesla followed the EPA rules when setting the mileage and W-hr/mile to a fare-thee-well. With a 2018 M3, a 2021 MY, and a 2023 M3 (sold the 2018), I've always gotten close to the EPA numbers. But I do live on the East Coast, where speeds tend to be somewhat slower, and I'm one of those drivers who doesn't play jackrabbit.
When the EPA decided, with good reason, to change the mechanism/procedure used to calculate the range/W-hr/mile, Tesla kicked right in and put in the new numbers based upon the new rules. Some people yelled, "Cheat!" because, well, why not. But they never broke any rules - rather, the opposite.
Next: The car's mileage estimators. In order of increasing accuracy, we have:
- The number at the top of the screen. The car takes the Best Estimate of the number of kW-hr's of charge in the battery and divides it by the W-hr/mile that's printed on the Mulrooney sticker, and displays the mileage until empty. You're driving on a cold day? With a head wind? With a tail wind? Going uphill? Going downhill? None of that is in there. Having said that, if it's the spiffy spring/summer/fall, there's nothing elevation-wise going on, and the wind's not blowing particularly, this estimate is vaguely reasonable.
- Energy Screen. Hit the triple-dot button in the middle of the bottom, pick the icon labeled "Energy", and stand back in wonder. In order:
- Right hand most tab is "Consumption". Has a plot of energy used on the Y axis and how far back it was in the X axis, where your current position is on the right. Not bad. You'll see the last hill you climbed, the last hill you drove down, any mad acceleration or deceleration, or when you moved from local roads to the interstate. It shows an average over the selected range (I think 5, 10, or 30 miles?) which, if you're going at a more-or-less constant speed, is reasonably accurate, and shows the range from this average. Nice when it shows, say, 196 miles to empty when the number at the top of the screen is showing 160. Not so much fun if those two are flipped, though.
- Left hand most tab has the strangest plot I've seen in a while, which shows estimated range vs. Official Range for the drive one is doing. Cute. But the real money is on the listing down below, where it shows a little bar chart of sorts with terms like "driving", Air conditioning, altitude, and three or so others. Each one of these items is either green (you're making it farther than "expected") or red (less far).
- The %battery at trips end. This is the number when you have your destination plugged into the NAV, and shows up in the box at the bottom of the screen which shows your distance to the destination and the %charge when you get there. THIS is the most accurate estimator. Going on local and superhighways? It's in there. Up a mountain and down the other side? It's in there. There's a windstorm heading your way and will hit in a half hour, either blowing you down the road or pushing you backwards? It's in there. It's ALL in there. One number, but it's as accurate as Tesla can make it.
And, just mentioning one other thing: The middle tab in the Energy screen has the energy usage you've been using while you've been parked. Interested in Sentry battery drain? Or running the heat/cooling while parked in Dog mode? It's in there. Handy when people are trying to figure out where their range hath gone.
Finally: A lot of the above depends upon an accurate measure of the contents of charge in the BMS (Battery Management System). Turns out, the BMS, while more accurate than a typical ICE's idea of how much gas is in the tank, isn't nailed in stone. About a year after getting our initial 2018 M3, the displayed mileage at the top had dropped from the initial 320 miles or so (dividing the displayed number by the %charge) to 299 or so. All of this was on short, local trips, 15-20 miles or so.
Then took a 900 mile trip south and back on a vacation, charging up madly at Superchargers, with the battery charge dropping down into the single digits and back up again. Lo and behold, after the first day, the displayed range number went right back up into the 320's. And stayed up there for a month or so, then started decaying back down again.
This got to be a recognizable pattern. Local driving, the estimated mileage drops 20 miles or so. Do long distance: Not right away, but after the 2nd or 3rd Supercharging session there it was, back up again. When the car was sold last year, the max number was around 309-311, about a 3% drop in displayed charge, not bad for a 5 year old car.
Deal is, being something of a reliability engineer, I can safely tell you that, over a large enough population of vehicles (or anything else), Some Of Everything Dies, sooner or later. It's not even necessarily wear; I mean, the occasional ICE car manufactured somewhere throws a rod or breaks a crankshaft. It's why there're warranties. So, does your drop in range mean that your car's got a defect? Probably not, most cars don't, and your drop in range kinda sounds like some of the above. But if it starts getting down into the 10% down range, contact Tesla. They got super-duper diagnostics for the battery system that can suss out the evil stuff. Or get you kicked out of the Service Center with a, "Really, don't be so
sensitive to these kind of things." admonition. If your decreased range gets down into 30+ miles, then bug them.
