Why Doesn’t the Jaguar I-Pace Go As Far As It Should on a Charge?
Last week, Jaguar finally received the EPA fuel economy rating for its I-Pace electric crossover, and it probably wasn’t what JLR was hoping for. According to the feds, the curvy ride is good for 234 miles of electric driving—a number that’s a few clicks shy of the 240-mile estimate the company had suggested would be the case.
That’s disappointing, of course, but not so far off the mark that potential owners should feel particularly cheated. On the other hand, when your main competitor is Tesla—whose closest parallel to the F-Pace is the Model X 75D, which has a smaller battery and weighs more, yet offers similar range—and you have Mercedes, Audi, and BMW nipping at your heels with their own new or forthcoming electric SUVs, every mile counts. (It didn’t help that the difference looks bigger than it is, with the drop taking it from the 240s to the 230s.)
Why that final estimate came in where it did, however, is a bit of a head-scratcher—especially because, in theory the results could have been even higher than the 240-mile projection.
As to what caused the lower-than-expected outcome, the easy answer is, well, lower than expected efficiency. But where those efficiency losses occurred is an important question for Jaguar. According to researchers at Carnegie Mellon University’s Department of Mechanical Engineering, who dug into the available data over the last week, it doesn’t actually appear to be a problem with the most likely target—the 90-kWh battery pack.
“What we’re seeing, even with the worst possible battery discharge efficiency, is that the numbers don’t check out,” said engineer Shashank Sripad, who conducted an initial investigation with colleague Venkat Viswanathan and others. “There is a chance that the motors are not efficient at all, or the way they have been incorporated into the powertrain might be causing the low efficiency.”
The CMU engineers frequently analyze new electric vehicles: comparing them against models they’ve developed detailed knowledge of, while factoring in drag coefficients, frontal area, mass, the rolling resistance of the tires, the battery discharge efficiency, and the total powertrain efficiency. With that data, Viswanathan explains, they calculate the battery pack size that would be required to achieve the rated range published by the testing agency as a result of its drive cycle—that is, the speed and distance covered in the test. (In this case, the agency being the EPA.)
“So if the battery pack we estimate matches the actual battery pack size, then the model [we created] checks out, and can be used to predict for another vehicle,” he says.
Using this methodology, the researchers anticipated that the Model 3, the smallest car in Tesla’s lineup, would get 310 miles of range from a 79-kWh pack, which was just one off from the 80-kWh pack that was eventually revealed. The model S estimate came to 315 miles from a 98-kWh pack, against the actual pack size of 100 kWh. The Model X trim level that most closely matches the I-Pace’s actual range, however, proved most telling. The researchers calculated that the Tesla would score 237 miles from a 76-kWh pack—again, just one off from the actual 75 kWh pack—and using that model, they expected the Jaguar to score 234 miles from a 74 kWh pack. But the 4,700-pound I-Pace, which has a 0.29 drag coefficient, has an actual battery pack size of 90 kWh. To put it another way, Jaguar’s car has 21 percent more battery than the 440-lb-heavier Tesla Model X (which, to be fair, has a lower Cd of 0.24), yet both vehicles offers the same range. The numbers suggest the I-Pace’s range should have been above even the 240 number Jaguar estimated—maybe as much 250 miles of range.
This could mean several things, Sripad says. One, that the I-Pace powertrain is about 22 percent less efficient than the Tesla’s; two, the battery pack is “software locked,” and only about 73-75 kWh of capacity is actually available; or three, the aerodynamics of the I-Pace aren’t as good as the manufacturer claims, which Sripad says is the least likely scenario.
“The drag coefficient would have to be close to twice, at 0.55 rather than 0.29, and it’s unlikely that the aero would get that bad,” he says.
The question, though, of why Tesla does so consistently well with its efficiency ratings points, again, less to the battery pack’s size and more to the overall package.
“Miles-per-kilowatt-hour is actually not dependent on the battery tech, but on the aerodynamics and overall energy efficiency of the powertrain per mile driven,” Viswanathan says. “[Tesla’s] drag coefficient alone is probably the best, and certainly in their class.” He notes that the Model 3, specifically, has the lowest drag coefficient of all passenger sedans, in or out of its price range.
Jaguar, for its part, hasn’t yet provided an explanation for the discrepancy between its estimates and the EPA’s. But the data seems to suggest that, had the I-Pace upped its game a hair or two at every link of the powertrain chain, it could have had Tesla on the run.