A non-scientific anecdote to add to the discussion:
I put 15 inch Civic rims on the back of my Miata to reduce RPM. New tire size is 185/65R15, the same width but larger diameter than the factory 185/60R14 tires.
RPM difference @ 80 km/h:
- OEM: 2587 RPM
- NEW: 2404 RPM
- 7.1% reduction in RPM
Difference in rolling resistance? Improved (I did a comparison test to the previous tires). Difference in aero drag? Unknown! (It raised the rear of the car by about 3/4 inch). Difference in rotational weight? Unknown!
So this is in NO WAY scientific, but the first full tank I had the taller tires on the car with similar driving patterns & speeds saw a ~10% improvement in fuel economy. BUT the tire change was done in addition to a number of other small efficiency modifications that were made at the same time.
I'm just guesstimating, but I think it's reasonable to say the tire diameter change on its own was good for a difference of a few percent.
View my fuel log 2015 Micra S manual: 5.0 L/100 km ... 56.5 mpg (Imp) ... 20.0 km/L ... 47.0 mpg (US) ...