Sheik,
Will your motor drive the rear wheel directly or are you planning to use some sort of a transmission to give you a clutch and gears? What about reverse gear?
No transmission. There's a lot of argument about the merit of a transmission in the world of electric vehicles, so I'll try to give you a greatest hits.
Electric motors, although they have all the available torque right off the line, still have a peak efficiency at a certain RPM. Going directly to the back wheel means you have to pick a certain ratio, so you have to pick between really fast off the line or top speed. A transmission can get keep you in peak efficiency and give you both top speed and off the line-performance, but it adds weight and complexity. And 6 speeds aren't really needed, two speeds would even be a big improvement, but nobody has a small enough, light enough, or robust enough two speed for a motorcycle. You're better off getting a more powerful motor and going higher voltage with more batteries (until somebody markets the right kind of transmission).
Some people have been experimenting with series and parallel switching for multiple motors, meaning you can have the motors see full current (amperage) at half voltage (LOTS of torque) and switch to full voltage half current (higher speed).
Jozzbikes Electric Ducati.There's a Ducati with this switching.
Reverse gear is handled entirely by the controller. If I wanted to I could have the bike go as fast backwards as forwards (but I don't want that....)