I will have to check what the tires were when I get back home, and report back. I do know the rims were 8" wide, vs the 7" wide Prius rims. The rim/tire combos are noticeably lighter when lifting. This is comparing between my wife's 15's and the 17's. I don't have a mass reading on both, so it's not a real comparison, but it is something I noticed.
Running the old tires on the back of the car would be an option, but we plan to sell off the 17" rims to someone looking to "upgrade" their ride. Anyone here looking for some 17's?
I agree, it could be a large number of factors that impacted the large change in FE. I am just glad it is up, way up
.