The EPA figure accounts for hot and cold condition testing, which the WLTP does not, and they can do it two ways. The first EPA protocol runs a five-cycle test, which finds how efficient the car would be in ideal conditions on the city and highway, alongside more testing in more extreme conditions to de-rate the car back down to what could be a more realistic estimation.
The other way to do it is to run only a two-cycle test, the city and highway cycles. But the EPA still requires a de-rating for a more conservative estimate and to avoid any chance of misleading customers. If an automaker chooses just the two-cycle test, a de-rating factor of 0.7 is applied to the estimate, cutting down the range.
Here’s a little more detail on the test procedure, from FuelEconomy.gov
Electric Vehicle - Adjustment Procedure used to Derive FE Label (Window Sticker) Estimates
EPA regulations require fuel economy, energy consumption, CO2 and driving range values listed on the FE Label (window sticker) to be adjusted to more accurately reflect the values that customers can expect to achieve in the real world.
EPA currently allows fuel economy, energy consumption, CO2 values, and range values listed on the FE Label (window sticker) for electric vehicles to be adjusted using one of the following methods:
- by multiplying city/highway fuel economy and range values by 0.7 and dividing city/highway energy consumption and CO2 values by 0.7
- using the derived 5-cycle method described in 40 CFR 600.210-12(a)(2) and EPA guidance letter CD-15- 15, June 22, 2015 (available here)
- using a method which is equivalent to the vehicle specific 5-cycle method described in 40 CFR 600.210- 12(a)(1) (with prior EPA approval) such as the method provided in Appendix B of SAE J1634 July 2017 Recommended Practice;
- using adjustment factors which are based on in-use data (with prior EPA approval). Currently, most EVs use the first or third method (the 0.7 factor)
If you do some backwards math and take the Taycan’s 201 mile de-rated EPA range estimate and divide it by the 0.7 de-rating factor, you get 287 miles. That means the Taycan must have achieved an estimated range of 287 mile on the EPA’s two-cycle test, which closely aligns with the WLTP’s 280-mile range estimate, as well as Porsche’s own third-party test resulting in 275 miles of range.
Keep in mind that this does not mean you can go back to other EVs sold in the U.S., divide by 0.7, and reasonably expect that number to be accurate. You have to know how the car was tested for certification, based on one of the methods outlined above.
Unfortunately, electric vehicle testing is complicated, both globally and locally here in the U.S., which can make it difficult for the average car shopper looking at a window sticker to understand.
But what’s actually happening is automakers are taking it upon themselves to protect their reputation by perhaps holding back their equipment a little bit to ensure reliability and consistent performance, not just the biggest number they can hit.
That, and the government is also keeping figures conservative to ensure buyers don’t blame them for unreasonable expectations on range, even if the EPA could do a little better job explaining exactly how a car can lose over 80 miles of range between driving in the U.S. versus driving it in Europe.