I am sure Zwift got their rolling resistance mode from some reputable source.
I did a quick search and found these values. So it all depend on what Zwift used for c on the normal roads. Lets assume the used bicycle tire on asphalt road (0.004) and for the dirt section
bicycle tire on rough paved road (0.008) that is double.
And since F=c*W and weight stay the same then the force to overcome rolling resistance will double.
