That fatbike version of the SON has the same electrical design and interieur as the standard SON28 (both versions have the same StVZO certification: ~K834), it's just heavier due to a wider body And that means 6 W (mechanical) energy required (with light/ 12 Ohm load) at 15 mph for an (electrical) output between 3 and 3.5 W. And the additional energy energy (compared to a good front hub) required at those speeds with the light off/load disconnected is only 0.5 W - 1 W. Your fatbike tires cost you significantly more energy