A paper published by SAE International has found that electric vehicles are far worse at matching EPA estimates than their gas-powered counterparts.
The paper compares EPA fuel-economy and range estimates to the results of Car and Driver‘s real-world highway tests, with the conclusion being that EVs fail to meet EPA’s range figures on average by a much greater margin than internal-combustion vehicles.
Authored by Car and Driver‘s testing director, Dave VanderWerp, and Gregory Pannone, the paper was presented last week at SAE International’s annual WCX conference.
The main finding is that ICE-powered vehicles typically meet or exceed the EPA-estimated highway fuel economy numbers, while EVs tend to fall considerably short of the range number on the window sticker. This calls for revised testing and labeling standards for EVs moving forward, according to the authors.
Based on Car and Driver‘s 75-mph highway test, more than 350 ICE vehicles averaged 4.0 percent better fuel economy than the values on the window sticker. However, the average range for an EV was 12.5 percent worse than what was stated on their labels.
Why the big disparity, though? One reason is the way the range is calculated, more specifically the fact only a combined number is presented to consumers – even though separate city and highway range figures are also calculated behind closed doors. The combined rating is then weighted 55 percent in favor of the city figure, where EVs typically perform better.
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As a result, the range estimates are inflated in favor of EVs, making the ratings harder to match in real-world highway driving. A solution proposed by the paper is to publish both city and highway range figures – as it already happens with fuel-economy estimates for ICE vehicles – so that shoppers get a more accurate picture of a vehicle’s efficiency.
Another cause for the skewed range figures is the way the EPA tests are conducted. Unlike Car and Driver‘s real-world test carried out at a constant 75 mph, the EPA’s cycle is variable, with the speed increasing and decreasing during the test.
This favors EVs, which are able to regenerate energy under braking, to the detriment of gas vehicles, which tend to be most efficient at a steady rpm. Obviously, it leads to higher range results for EVs.
Furthermore, the EPA’s highway cycle is conducted at significantly lower speeds than Car and Driver‘s 75-mph test, with the initial EPA results then multiplied by a reduction factor to simulate the effect of higher speeds.
The reduction factor is another issue highlighted in the paper. Automakers can choose between running a two-cycle test – where the data is multiplied by a standard 0.7 adjustment factor – or a five-cycle test in an attempt to earn a smaller reduction factor, resulting in a higher label figure.
A consequence of that is the range figures aren’t perfectly comparable across different vehicles. The authors of the paper propose that the EPA shift the reduction factor closer to 0.6 and run the same test procedure for all cars.
