If you’re shopping for a new electric car, there are a few different facts and figures that you might want to consider before making the battery-powered plunge. The big figure is the range of your EV, as that shows how far you can travel on a full battery, while the MPGe rating tries to offer an easy way to compare efficiency in electric cars and gas-powered models. However, a new study has found that ratings for many EVs are far less reliable than for their gas-powered counterparts.
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The study, published by industry body SAE International, compared the range ratings for 365 gas-powered cars and 44 battery electric vehicles. To do this, Gregory Pannone, the former head of fuel economy at Chrysler, and Dave VanderWerp, director of vehicle testing at Car and Driver, ran the cars through a variety of tests.
Through the test drives carried out with internal combustion engine-powered cars, the researchers found that cars performed four percent better in terms of fuel economy than the figure they were rated for. In fact, the team found that 66 percent of gas-powered cars tested achieved an MPG figure higher than their labeled value.
However, the results weren’t so positive for the battery-powered models that the team tested. The paper reported:
“Most BEVs tested to date fall short of both their electric consumption and range label values. For BEVs, the difference between the label and on-road consumption and range is further exacerbated by other factors, such as extreme temperatures and suggestions by automakers to charge to less than 100 percent to extend battery life.”
Across its testing, the team found that EVs performed 12.5 percent worse than their rated range on average. In fact, just ten of the models included in testing managed to surpass their range estimates, accounting for only 17 percent of the 44 cars in the study. The researchers said that these results would “not be expected if the labeling process for BEVs was equally robust in capturing the on-road adjustments.”
The disparity between an electric car’s real-world range and the one its manufacturers predict is all down to the way it’s calculated. According to the paper, EVs are allowed an adjustment factor of 0.7 or higher, which means that the calculated range is multiplied by 0.7 to give a range estimation. In practice, this means the estimating is 30 percent lower than the calculated range.
In contrast, gas-powered cars must have an adjustment factor of 0.7 or lower, which means that the MPG rating is more conservative. This adjustment factor, coupled with things like temperature and battery health, all mean that real-world range for BEVs is more likely to be lower than advertised. The paper added:
“Consequently, these results support the need to re-evaluate the labeling procedures for this emerging technology as it continues to become increasingly prominent in the marketplace.”
This conclusion is clearly something regulators have also come to, as the U.S. government recently announced that it was overhauling mileage ratings for EVs that are sold stateside. Earlier this month, regulators announced they were cracking down on MPGe estimates for EVs, which would slash some ratings by as much as a third if they went into effect.