Originally Posted by WRXVT
Interesting... i wonder what Luke from tirerack says about this. What you say makes sense, however It seems weird that an S rated 70 series tire may have similar performance to a Z rated. It just seems that the combination of a lower profile and higher speed rating tire would probably improve performance.
Well, yeah, lower profile is going to improve steering response and be a little more resistant to sidewall rollover, but you are only talking about 12mm less sidewall here. Most tires of a particular model come in a narrow band of sizes so you aren't going to be comparing a 70 series to a 45 series.
Speed rating itself is not indictative of any performance enhancements. Really, there isn't much functional difference between Z and V rating anyways. Both are 149mph, it's just that Z doesn't have a defined upper limit because it's an older rating (149+mph).
I find it odd actually that the tire has a Z rating, that implies that it was tested awhile ago since Z ratings are depricated now and replaced by V, W, and Y.