I have not used a hub drive bike for mountain biking.---I cannot imagine that with all the weight in the rear end of a hub drive that the off-road performance would be acceptable.---Possibly it would work ok for logging roads etc, however for more extreme technical single track work, the better center of gravity offered with the new Mid-Drive format comes close to duplicating the normal Mt. bike offerings.---I think that the chances of the front end coming off the ground with a REAR hub drive at extreme uphill angles would create problems ---IMHO