How do you know the wheel barring are bad?

A grinding or abnormal noise at the wheel is a good sign the bearing is bad. Unload the bearing by moving the vehicle left or right while moving. If the noise comes and goes when doing this, the bearing is bad. The only positive way to verify this is to remove the bearing and look at it. Pitting, scouring, and any other signs of wear indicate the bearing needs replacing. Be sure and replace the race if it is not perfect.