Using VOX on a bike is probably never a great solution. Beyond the technical issue of getting it to transmit when you want and not due to wind noise is one thing, but from my experience, there are a lot of other things one says and noises one makes while riding that would trigger it... sounds and words you may not want to be transmitting!
Think about it... Just saying.
Get a boom mic with something to cut the wind noise and a PTT button.. or get a small hand mic.