I'd have to see how each was written out but in each case the R should stand for radial and the Z is a speed rating in excess of 149 mph. On both tires there should be a service description with 2 numbers and a letter. It should be right after the tire size and tells you the tires load index and speed rating. The markings should look something like this...
W supersedes or refines the Z and means 168mph rated.
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