My partner has become a fan of my e-bike and now wants her Specialized converted to electric. What's our best bet for a motor hub and controller that would suit this bike? The bike has Shimano discs on the back, plus an 8 cog cassette and these would need to fit onto the new hub. She wants to stay road legal, so the usual 250w/15mph limits apply. Range doesn't need to be colossal - a 12Ah battery pack should do the trick.