I took a look at the EPA FE test data for the 2017 C-Max, Priis, Niro and Ioniq for comparative purposes. Based on the data, I constructed the following table of "expected" FE for the Priis, Niro, and Ioniq based on the differences between the road load HP coefficients for the vehicle ahieving the highest FE used in the dyno FE testing. Of course, one can always operate vehicles to achieve more / less FE that expected and the oveall efficiency of the powertrain will affect actual FE.
The interesting observation is that the Prius and Prius V numbers below are in sync with the Priis EPA ratings. Not so with the Ioniq and Niro. The Priis and C-Max data also appears to be in sync with the average FE being shown in Fuelly. For example, if you drive the C-Max and get 40 mpg in the C-Max, you might expect to get 48 mpg in the Ioniq, 44 in the Niro and so forth based on the difference between the C-Max and other vehicles RLHP. Kia does IIRC claim there ICE is 40% efficient. I don't believe the C-Max or Priis engines are that efficient. Time should tell as people report their FE to Fuelly.
This data is based on the RLHP curve data attached (sorry I can't upload in gallery as I reached my limit so I have to attach).
Test data 1.JPG 112.35KB
Test data 2.JPG 119.13KB
Edited by Plus 3 Golfer, 14 August 2017 - 06:13 AM.