sorry, overlooked.   Non paratheticals are up to 186 mph.  In parantheticals, over that (sometimes by a huge amount).  Y itself is for "exotic sports car tires" as opposed to Z, for example, "high-performance vehicles" defined as 149+ MPH.  Personally, I've always felt the alphabetical tire speed listings got all F-ed up once you hit the V classification, after that, it's just BS.  Check the stats for each specific tire, or surf at your own risk.