ZR in a tire size

How to read it

USTMA and Bridgestone say any tire with a maximum speed above 240 km/h (149 mph) may, at its maker’s choice, have a Z in the size designation, and a tire rated above 300 km/h (186 mph) must. For those, USTMA adds, the service description must be a Y in brackets, as in (93Y). A ZR size on its own says only that the tire is rated above 240 km/h; the exact rating is in the service description, where there is one.

Also searched as: Z rated tire, ZR tire, Z speed rating.

Reading ZR with a service description

USTMA’s and Bridgestone’s examples: P275/40ZR17 alone is over 149 mph, and they refer to the tire’s maker for the figure; P275/40ZR17 93W is 270 km/h (168 mph), the same as P275/40R17 93W; P275/40ZR17 93Y is 300 km/h (186 mph); P275/40ZR17 (93Y) is over 186 mph.

Z as a speed rating

BFGoodrich says Z was once the highest rating, at 149 mph and above, until W and Y were added for the speeds of exotic sports cars. Bridgestone Australia and Pirelli still list Z on their charts as over 240 km/h (149 mph).

NHTSA’s wording

NHTSA’s booklet says tire makers sometimes use ZR on tires rated above 149 mph and must use it above 186 mph; Ford’s manual repeats it. USTMA’s chart adds the rule for the bracketed (Y).