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Unless the rules have changed in the last ten years the Feds limited motor power output to 750 watts and a maximum flat land speed of 24 mph to be considered a bicycle in the U.S.
I built a kit version in 2006 with a 750 W hub motor that would go 30 mph pretty easily. Just rarely ran it that hard. Powered it off two 36 V Dewalt battery packs connected in series for a 72 volt system. Still runs but I don't use it much any more. The good thing about the hub motor is that is has minimum maintenance. Bad thing, fairly heavy. I hear they are much lighter now for the same power output.
My total original cost was under $1000 including the motor, controller, batteries, and bike. Bought a used Gary Fisher mountain bike because I figured I would need a heavy duty frame to handle the power. I was right.
I'd probably try an inline motor if I were to build a new one because they are lighter weight for the same power output. But then there is more maintenance, alignment concerns and mounting issues. Nothing major, just things that need to be considered.
JJ
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