What are the differences between a ZR or R tyre?

The Z in ZR corresponds to an old label used by manufacturers to indicate that the speed index is higher than V, i.e. 150 mph. Thus, a ZR tyre has a speed index of V, W, or Y.

R indicates that the structure is RADIAL.

So, VR indicates that the tyre has a RADIAL structure and a speed index equal to V.

There is therefore no difference between a ZR or an R tyre with the same speed index.