question about rim size affecting speed

Ok me and my friend have been discussing this for a while. Im not sure who is right we both arent very sure to tell you the truth. When you have custom rims that are bigger than stock does this speed you up or slow you down. I say its all about the weight of the rims. But does size really play a big difference say going from 17s to 18s?

his car is slower now that he went from 15s to his custom 17s and we know its because of weight, but if they weighed the exact same do you think this would make a difference in speed?? just food for thought and im kinda curious myself.