Speed ratings are determined on a 67" flywheel in a test lab. Tires are run in ten minute speed steps (initial speed determined by rating being attempted) with speed being increased 10 kph for each step until failure.

SPEED SYMBOL..............................SPEED CATEGORY
Q................................................. .............99 MPH
R................................................. ............106
S................................................. ............112
T................................................. ............118
U................................................. ...........124
H................................................. ...........130
V................................................. ...........149
W................................................. ..........168
Y................................................. ............186


Z Rated tires are considered "Open Ended Category" where the tire must match the speed capability of the vehicle it is to be sold with (above 149mph).

Failures are usually due to heat-buildup related issues, resulting in mechanical separation of components.

Don't confuse time on a web board with knowledge

Ferd
(Noobie with Integras, oldie with tires)