posted February 07, 2003 06:19 PM
Look at the chart below:Speed Rating....Max Speed
.....S............112
.....H............130
.....V............150
.....Z...........over 150
(I hope you'll excuse the dots, but this software takes out excessive spaces and makes the chart look really funky.)
That was what the chart looked like for many years. The purpose of the Z rating was to be provide a place for specialty tires where the speed capability of the tire was matched to the speed capability of the vehicle and it was to be such that a given vehicle took a given tire size and vice versa, so there could be no mixup.
But because there was a pretty big gap between S and H, and because there were too many vehicles capable of over 150, it was recently decided to add:
.....T............118
.....U............124
.....W............169
.....Y............188
Now what to do about Z? Can't change it because you have to "grandfather" all the old specs. Solution: Leave Z right where it is - opened ended and suggest that all tire manufacturers adopt W and Y ratings and use Z only when they can't use W and Y.
This is a long way of saying Z is still the highest rating, even though it doesn't appear that way.
Another long winded explanation:
The reason Volvo put Y rated tires on the vehicle is 1) so they could qualify the vehicle in other countries that don't have top speed restrictions without having to change the type of tire and therefore redo the springs, shocks and sway bars. and 2) a higher speed rating is an increased safety margin.
Hope this helps.
[This message has been edited by CapriRacer (edited February 07, 2003).]