2013 Tesla Model S electric sport sedan [photo by owner David Noland]Enlarge Photo
At this rate I'd be totally out of energy at 182 miles. Way too close for comfort.
But I was pretty sure that the culprit was elevation. From previous trips, I'd learned that elevation changes have a huge effect on the range of the Model S.
For example, when I make the 60-mile drive from my house (elevation: 423 feet) to New York City (sea level), I typically average 270 Wh/mi in warm weather. The return trip, slightly uphill, averages about 310. A mere 400-foot elevation change over 60 miles alters efficiency by almost 15 percent.
I'd checked the elevation of Danville (578 feet) before I left, but hadn't paid attention to the intervening terrain. Hopefully, I'd soon begin descending.
Tesla Road Trip from MD to CT, Feb 2013 - Tesla Model S cars at Delaware SuperCharger locationEnlarge Photo
Sure enough, as I passed Wilkes Barre, the e-meter began to come back down toward 320 kWh/mi, then 310. I breathed a sigh of relief; I had it in the bag.
(I later determined that I'd reached a peak elevation of about 1800 feet along I-84 just east of Wilkes-Barre.)
By the time I got to Danville, my energy usage had dropped to 295 wH/mi--right in the middle of my target zone.
The range meter read 24 miles when I finally arrived at a funky farmhouse. It was home to an affable banjo-picker named Mark Doncheski, two Corvettes, and a Tesla Roadster. Mark had agreed to make his Tesla charger available to Sherman and me.
Range meter quirks
As I'd anticipated, the guess-o-meter didn't quite square with reality. I'd started with 199 indicated miles and driven an actual 168. That's a 31-mile difference. Seven miles got lost somewhere.
The old-reliable e-meter told me I'd used 49.4 kWh of juice for the trip. That left 10.6 kWh--enough to drive an additional 36 miles at my trip average of 295 wH/mi. (More, at slower speeds.)
Theoretically, I had 12 more miles remaining than the guess-o-meter indicated.
This squares with an unofficial on-line Model S owner's manual compiled by Tesla fanatic Nick J. Howe. According to Howe, the 85-kWh Model S actually has 17 miles "in the tank" after the range meter reaches zero.
Prorating for my 60-kWh battery, that's pretty close to my theoretical 12-mile buffer.
Bottom line: I can still probably limp to some sort of electrical outlet or charger even after the range meter hits zero. Frankly, I never want to have to confirm that.
Sherman arrived five hours later in a brown P85, accompanied by owner Fred Glomb and a support truck towing a trailer. Cruising at a steady 62 mph, they'd covered the 251-mile leg from Ohio with 20 miles to spare.
Over a late dinner in Mark's kitchen, we talked Tesla and the upcoming race till well past midnight.
2012 Tesla Model S Charging ConnectorEnlarge Photo
Out of the pizza-fueled discussion came a startling conclusion about Model S driving strategy for the race: Cruising speed is basically irrelevant. Any time gained by going faster between charging stops is almost exactly negated by the increased charging time.
(This conclusion assumes an 85-kWh car equipped with Twin Chargers that is charged from a 20-kW Tesla High Power Wall Connector--the fastest possible charging scenario along the race route, which had no Superchargers anywhere near.)
The breakdown: Over a typical 240-mile leg, driving 70 mph would save 56 minutes over a 55-mph speed. Based on the speed-vs-range graph on the Tesla website, the faster car would use about 18 kWh more energy. Charging time to replace that extra 18 kWh: 54 minutes.
Of course the eventual arrival of more Superchargers will eliminate such fascinating threads of discussion.
Next morning, Sherman's car was loaded onto the trailer for the trip back to Michigan. I topped off my car and retraced my route home, logging virtually identical numbers for the return leg.
My personal takeaway from this exercise was a practical range limit for my car: 180 miles in warm weather, 150 miles in the cold.
Bring on the East Coast Superchargers. Please.