[metroschultz]

?"Your Guess is as Good as Mine"?

I would believe that rolling resistance plays a part in the reduction factor,
BUT,
Don't discount the aerodynamics of the two tire styles.
OEM = taller, wider, more contact patch
Donut = shorter [slightly], narrower, less contact patch, and they present a round face to the wind.
OEM tires present a large flat face to the wind.
many variables in one component.
changing all those variables at once = big difference.
I have found a source fro 145 80R 13 tires.
when my current tires are worn out I will replace them with the 13's
Your video just pushed me over my decision hump. I was waffling because this change requires the purchase of new rims also.
But I haven't been to the bone yard in a while, they probly miss me.
Schultz