See my related post here:
https://electricbikereview.com/forums/threads/gear-upgrade-for-radrunner.33173/post-318164.
I think or maybe should say have experienced what EBJ mentions about the fit between the rear dropouts or Over-Locknut-Distance (OLD). If you have a different experience with up fitting the 750w bafang motor into your single speed rad runner frame please post. Maybe there is a better way, swap axels? It was quite a task to fit the new motor into the frame by reducing the 750w bafang axel shaft shoulder not to mention the removal of the gear. The correct way to r & r the gear is to have a special removal tool and not use a punch and hammer like me. Believe it or not, but the gear was not marked up or damaged. The steel is quite hard. If there is interest I can create a new thread and try and narrate and post photos about the "fun" of up fitting a true 750w bafang motor into a rad runner (single speed).