Shall we call the police?

Yesterday when me and my friend were walking home from school,we saw a man in a silver car speeding down the road.We watched him get to the corner, and as he turned he skidded and a bit of his car wheel lifted off the road.We tried to get his number plate but he went so quick we couldnt get it. Then the next day(today) we saw the exact same man in the exact same car going really fast again and we actually got his number plate.P.S where we saw him driving was in an area where loads of children walk home from school. Should we ring the police to tell them what we saw or do you think we are wasting there time?