unime

I don't think you appreciate the steepness of the road our friend in Chiapas has described. Its slope is the same as an intermediate ski slope and although I have ridden straight down such ski slopes (with the MTB director of the resort in the 1980s), and let me assure you they are freakin' steep! According to this bicycle calculator, a strong rider would manage only 1.7 mph up a slope like that. Probably closer to 1 mph on the steeper sections. Even with 500 watts of combined power the speed would only be around 4mph, far too slow for a hub motor to work effectively.

Maybe another comparison will help. Trail guidelines in the US suggest a 10% maximum grade and 5% overall grade. There are exceptions, to be sure, but we are talking about 30+% slopes here. I don't believe that bike trails often have slopes this steep, certainly not for sustained distances.

Last, consider this: There is a dirt road that goes almost straight up (with one dip across a pass) to some radio towers that I like to ride. It has an average slope of 10% and a maximum slope probably in excess of 20% (just a guess - I haven't measured). With modest effort, I can maintain a 5-6 mph pace up the steep sections on my Optibike with 800 watts of power driving the bike's low gear. Anything slower and the motor really bogs down - enough that riding any slower makes me worry. A comparable hub motor (geared or otherwise) would be running with abyssmal efficiency, providing little assistance and likely overheating.