Subject: how does kinetic friction relate to velocity of movement

I am trying to work out the origin of possible "frictional"losses when a 
wheel spins freely.I determined the average velocity and kinetic energy 
during the wheel run down period from this power was determined.I 
determined the "frictional torque" by regressing power and velocity. The 
answer always gives a constant "frictional torque". I was told that 
dynamic friction should depend on velocity of movement, this does not seem 
to hold true any ideas?

Re: how does kinetic friction relate to velocity of movement