Quick post-

First W is Z rated... Its a sub rating beyond Z.

Z rating is for 149+mph. This is an old rating system that is currently out dated. Since some vehicles are capable of well over 149.. Tire manufactures have come out with the sub set.. W, Y, etc. The tire is still Z rated because Z is open ended; it is any tire capable of over 149. The W and Y designations simply specify at what speed its max capability is. So therefore a W is not better or worse than Z; it is Z.

Next- See my posts (more than one):
https://www.crossfireforum.org/forum...?p=17236#17236

Has more info on why you should maintain the correct tire- Beyond reasoning in court if a lawyer got hold of you