Quote:
Originally Posted by ThaCamaroKid
Y rated tires are 'technically' a higher speed rating than z rated tires.
Reason is long and boring, but essentially if a tire is Y rated it is the highest rating, and if it is ZR in addition to being Y rated just means it is speed rated for 149+ so it is a bit redundant. W and Y rated tires are the highest ratings,
Z/ZR is actually 149+
W is 168
Y is 186+
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almost...
"Z" isn't a real rating anymore. I beleive it use to be years ago. More of a remnant now. As it says above, if it has a Z in the size description (ie; P275/40ZR20), then it is "above" 149.
There will always be a 'service description' after the size description that shows the load index "number" and the speed rating "letter":
105Y or (105Y)
V is up to 149
the following can have "Z" in size description:
W is up to 168
Y is up to 186
(Y) is 186+... the parenthesis are important...which is to say, you need to verify the actual top speed limit with the tire manufacturer.
Note that the top speed is also guided by the load and the pressure... in other words, it would not be reasonable to expect a fully loaded tire at 35psi to hold together in a top speed run