What is the difference between R and ZR tyres ?
ZR basically means the tyre is adapted for speeds above 149 mph. ZR tyres includes the speed ratings V(149mph), W(168mph) and Y(186mph).
Before 1990, the manufacturers used "ZR" to mean high performance tyres before the ratings got refined with W, Y…
Nowadays, the marking ZR is not relevant anymore but it is still used in the catalogues of manufacturers and tyre retailers.
Look for the speed ratings V,W,Y to find the modern equivalent to ZR tyres and not for the marking ZR.
What really matters is the speed rating (V,W or Y).