Life With Tesla Model S: Pushing the Range Limits In 60-kWh CarLife With Tesla Model S: Pushing the Range Limits In 60-kWh Car

2013 Tesla Model S electric sport sedan [photo by owner David Noland]
In the eight months I’ve owned my 60-kWh Tesla Model S, I’ve never had occasion to drive it more than 120 miles, comfortably within the car’s  EPA-rated 208-mile range. The phrase “range anxiety” was not in my lexicon.
But last week, I got an invitation from Don Sherman, Technical Director of Car & Driver magazine, to meet him in Danville, Pennsylvania. It’s 168 miles from my home in New York’s Hudson Valley.
Sherman was making a dry run for an upcoming article about a 700-mile cross-country race in a Model S–and Danville, just off Interstate-80, was going to be a charging stop.  We’d e-mailed back and forth about Model S driving and charging strategies, and this would be a chance to meet and compare notes.
The journey seemed short enough to be eminently doable–yet long enough to engender, if not range anxiety, then at least acute range awareness.
Fast and hilly
Although I supposedly had a 40-mile cushion in the 208-mile EPA range, I knew very well that my mileage may vary. 
2013 Tesla Model S [photo: David Noland]
I was planning to drive fast, from 70 to 75 mph along the Interstates that made up most of the route. The terrain was hilly. There would be a prevailing headwind. And the advancing fall season promised cooler temperatures.
All of these factors would eat into range.
100-percent charge
In preparation for the trip,  I set the battery charge level at 100 percent, the first time I’d done so.
Previously, I’d always used the  “standard” setting, 90 percent of capacity. To get a full 100 percent, you set the charger to “range” mode, which Tesla recommends only when maximum range is necessary.
(The reason:  Lithium-ion batteries degrade more quickly when charged to 100 percent of capacity.)
A couple of months ago, a software update from Tesla allowed the charge limit to be set at any level. Tesla recommends 50 to 90 percent for everyday driving. I had settled on 75 percent, which was plenty for my normal driving routine.
But for this trip, I set the charger to 90 percent the night before, then topped off the battery to 100 percent before departure the next day. The topping-off process took longer than I anticipated; charge rate dropped from the usual 10 kW to about 3 kW for the last few kilowatt-hours. 
As I rolled out of my driveway, on an unseasonably warm Indian Summer day, the range meter read 199 miles.
David and Adam Metcalf beat 400 miles on a charge in a 2012 Tesla Model S (Image: David Metcalf)
Vanishing regen
The first thing I noticed was that the regenerative braking virtually disappeared with the 100-percent charge.  Charge rates in max regen can approach 40 kW,  way too much for a nearly full battery.
Going down a long, steep hill near my house, I actually had to use the brakes. Damn! Wasting precious energy already!
Fortunately, full regeneration came back quickly, within 10 miles.
Efficiency readouts
I don’t have a lot of faith in the Model S range meter. Its number is a projection based on rule-of-thumb efficiency assumptions, battery temperature, and a safety fudge factor.  (New York Times reporter Jonathan Broder famously fell victim to wildly fluctuating range numbers.) I call it the guess-o-meter.
Instead, I monitor the  dashboard readout of trip efficiency, measured in Watt-hours per mile. During my earlier shorter stints of highway driving, in warm weather, I’d averaged  290 to 300 Wh/mi.
I figured if I could maintain that level of efficiency, I’d make it to Danville with about 30 miles to spare. The Wh/mi reading thus became my prime focus for the trip.
Initial anxiety
For the open stretches of Interstate, I set the cruise control on 74 mph. (I figured no self-respecting cop would stop me for breaking the speed limit by single digits.
Forty miles out, along I-84, the e-meter settled in at around 310 Wh/mi. With the usual minor ups and downs for hills, the number crept steadily upward as I crossed into Pennsylvania.  By the time I reached Wilkes-Barre–about halfway–it was reading 330.
Not good.

2013 Tesla Model S electric sport sedan [photo by owner David Noland]
At this rate I’d be totally out of energy at 182 miles. Way too close for comfort.
Elevation changes
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 location
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.
Tesla talk
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 Connector
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.
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