I am buying new tires and posted a thread in the 355 section and talked to supposed experts on the subject, but I can't get a straight answer: Which are better and why, Z-rated or Y-rated tires???
Z rating has been used for over 10 years now and was originally meant as good for over 149 mph. I guess they figured there would never be a need for anything above the 149 and above rating. Y just means tested to be fine to at least 186. I don't feel the speed rating on either Z or Y will generally make it a better tire. I have seen Z rated tires with a Y in parenthesis meaning they are z-rated but capable of over 186mph. Speed rating just means it should hold together at the recommended MPH, which is important if your running the Silver State or something like it. There are R rated compound tires that have tremendous grip but are only recommended to 150 mph or so. Any W, Z or Y tires should be fine for a street car even running a track event at Pocono with its long straightaways.
I'm no expert but in reading and conversation with people who know more than me I have learned that there is in fact a difference, and it has to do with more than just the maximum speed a tire is capable of. Just as an aside: once upon a time you could buy a Porsche 911 with a redline on the speedometer at 130 mph because it was a "comfort" version or some such rubbish, and they fitted HR rated tires to soften the ride. Late '70s IIRC. But back to your question: the higher standards a tire is built to, the better it will perform in all conditions, not just top speed. In my case I spring for the ZR rating when HR would do nicely as far as top speed goes. I hardly ever take my 1988 VW above 130 mph (go ahead and laugh, observed top speed is 132 mph) but I do tend to lean on the tires more than most people and want the best rubber I can get. To wit: Image Unavailable, Please Login
There is a good explaination of all the ratings at the Tire Rack site. Here it is: Early tires had their speed rating symbol shown "within" the tire size, such as 225/50SR16. Tires using this type of branding were not to have been produced after 1991. 225/50SR16 112 mph, 180 km/h 225/50HR16 130, 210 km/h 225/50VR16 in excess of 130 mph, 210 km/h Beginning in 1991, the speed symbol denoting a fixed maximum speed capability of new tires must be shown only in the speed rating portion of the tire's service description, such as 225/50R16 89S. The most common tire speed rating symbols, maximum speeds and typical applications are shown below: M 81 mph 130 km/h N 87 mph 140km/h Temporary Spare Tires P 93 mph 150 km/h Q 99 mph 160 km/h Studless & Studdable Winter Tires R 106 mph 170 km/h H.D. Light Truck Tires S 112 mph 180 km/h Family Sedans & Vans T 118 mph 190 km/h Family Sedans & Vans U 124 mph 200 km/h H 130 mph 210 km/h Sport Sedans & Coupes V 149 mph 240 km/h Sport Sedans, Coupes & Sports Cars When Z-speed rated tires were first introduced, they were thought to reflect the highest tire speed rating that would ever be required, in excess of 240 km/h or 149 mph. While Z-speed rated tires are capable of speeds in excess of 149 mph, how far above 149 mph was not identified. That ultimately caused the automotive industry to add W- and Y-speed ratings to identify the tires that meet the needs of new vehicles that have extremely high top-speed capabilities. W 168 mph 270 km/h Exotic Sports Cars Y 186 mph 300 km/h Exotic Sports Cars While a Z-speed rating still often appears in the tire size designation of these tires, such as 225/50ZR16 91W, the Z in the size signifies a maximum speed capability in excess of 149 mph, 240 km/h; the W in the service description indicates the tire's 168 mph, 270 km/h maximum speed. 225/50ZR16 in excess of 149 mph, 240 km/h 205/45ZR17 88W 168 mph, 270 km/h 285/35ZR19 99Y 186 mph, 300 km/h Most recently, when the Y-speed rating indicated in a service description is enclosed in parentheses, such as 285/35ZR19 (99Y), the top speed of the tire has been tested in excess of 186 mph, 300 km/h indicated by the service description as shown below: 285/35ZR19 99Y 186 mph, 300 km/h 285/35ZR19 (99Y) in excess of 186 mph, 300 km/h As vehicles have increased their top speeds into Autobahn-only ranges, the tire speed ratings have evolved to better identify the tires capability, allowing drivers to match the speed of their tires with the top speed of their vehicle.
