Tesla's Musk releases datalogs for NYT test drive

Perhaps you have been following the dispute between the New York Times and Tesla Motors. In summary, on February 8 Times reporter John M. Broder recounted a sometimes slow, cold test drive of a Tesla S from Washington, D.C., to Groton, CT, and back to New York City—with one leg on the back of a flatbed truck with a depleted battery.

Publication of that article prompted a tweet from Tesla CEO Elon Musk: “NYTimes article about Tesla range in cold is fake. Vehicle logs tell true story that he didn't actually charge to max & took a long detour.”

Yesterday, Musk released the vehicle datalogs. The datalogs show vehicle speed, battery state of charge, rated range remaining, and cabin temperature setpoint, all vs. distance traveled, and they tell a story that's quite different from the one recounted in Broder's article and highlighted in an accompanying graphic.

As an example of the discrepancy, Broder writes that 68 miles after charging the car in Delaware (for a total of 182 cumulative miles from Washington), he noticed that “…estimated range was falling faster than miles were accumulating…. I began following Tesla’s range-maximization guidelines, which meant dispensing with such battery-draining amenities as warming the cabin and keeping up with traffic.” He says he turned the climate control to low and set cruise control at 54 mph. With range anxiety increasing as he neared New York, he writes, “…my feet were freezing and my knuckles were turning white.”

In contrast, the datalogs show the cabin setpoint temperature to have been increased as high as 74° and never falling much below 70° as the vehicle approached New York. Similarly, the logs show average speed during this period of 60 mph, not 54.

There are also discrepancies in charge levels reported by Broder and shown in the datalogs. Broder, for example, says he remained at a Delaware supercharging station until he got a “charge complete” display; the datalogs show the charge level reaching only 90%. At a subsequent charging station, Broder seems to acknowledge that he did not completely charge the battery, only enough to provide an estimated range of 185 miles—more than what he intended to cover before returning to the station. The datalogs show a 72% charge at that point.

Most alarmingly, Broder reports that in 10° overnight temperatures, the estimated range dropped from 90 to 25 miles while he slept. Broder says a call to a Tesla official resulted in advice to “condition” the battery by running the heater on low to recover the lost charge.

Musk's blog post doesn't directly address this issue, but he does write, “…our highest per capita sales are in Norway, where customers drive our cars during Arctic winters in permanent midnight.”

Perhaps Broder's white knuckles as he approached New York were physical manifestations to range anxiety rather than a response to cabin temperature. Or perhaps not. We will await any response from the Times to the released datalogs.

Both Broder's article and Musk's response that accompanies the datalog charts make interesting reading.

Meanwhile, I have a post here on lessons that should not be learned from this episode.