bike is on main road, you are not.
whether he is speeding or not, doesn't really matter that much
since you are the one making the U-turn, the bike has the right to
move forward on his side of the road.
you will win this if it was a traffic light and you had the
right of way to turn (right turn arrow) but since it is just a
sign, you have to watch out for anything.
if he hit you when you were not moving then you might have a
case and you need eyewitnesses at least to prove that you were a
stationary vehicle and the guy bumped into you instead of you
hitting him while turning.
but that's what i think, maybe someone else has a different
view