Range against the machine: A tale of two Teslas

With the advent of the Tesla Model S's latest variant, the 691-hp, all-wheel-drive P85D, one big question is how all that horsepower affects the driving range, since it uses the same battery as a rear-drive 362-hp Model S 85.  So we set up a little duel, pitting our new P85D against our two-year-old Model S 85. The test consisted of a long highway cruise, from our central-Connecticut test center up to Western Massachusetts and back.

The point was to compare them using a typical consumer's approach to a long-distance trip, which means lots of time on the expressway at about 70 mph. By the finish line we found that the more powerful, all-wheel-drive P85D did indeed have a shorter range, but not by much: just 20 miles less, in fact, after a 190-mile trek.

If someone wanted to squeeze out more miles, they could tool along a country road at 45 mph. But a slow meander probably isn't what most people have in mind when they actually want to get somewhere.

In this case, we started by fully charging both our Teslas in their "trip" mode, which makes more of the batteries' capacity available than the everyday commute mode does. Then my colleague Eric Evarts and I took a jaunt from our central-Connecticut test center to Deerfield, Mass., 95 miles away. To minimize variations we kept up a nominal speed of 70 mph with the climate controls set to 68 degrees. One car led on the outbound leg, the other on the return. It was a perfect spring day with an average temperature of 58 degrees through the trip.

We started out with 254 miles of predicted range showing on the 85 and 252 miles indicated on the P85D. When we arrived at Deerfield 95 miles later, the two cars had 144 and 136 miles left, respectively. After 45-minute lunch break, without recharging, we headed back onto I-91 South. Returning to our starting point in East Haddam, CT, our standard Model S 85 (the blue car) had 48 miles of remaining range, while the red P85D showed just 27.

For the record, the P85D is 268 pounds heavier than the regular 85 and likely the wider, lower, stickier performance-oriented tires of the P85D contributed to the difference.

Tesla's latest software, which both our cars have, directs you to Tesla Supercharger sites near your route. On the ride back, the P85D's display screen urged me to visit the West Springfield, Mass. Supercharger. But since I could see I had enough range left to reach our homeport with relative ease, I passed up the chance. No disrespect to Springfield, of course.

If we had extended the trip, keeping the same pace, we estimate that the regular 85 would have gone as far as 230 miles and the P85D could have covered 210 miles before the white-knuckle "range anxiety" known to all electric-vehicle drivers began in earnest.

—Gabe Shenhar