Hi,
The Brigestones you mention are Porsche approved see:
http://p-car.com/technical/tires.htm
So far as being
Y rated, this is not a problem whatever. A
Y rated tire is designed to be driven for "extended periods of Time" at speeds up to 186MPH.
The Speed Rating of a Tire is really an indicator of the Tire's ability to manage the Heat which it generates. If the Tire cannot shed this Heat, it compounds, or builds-up, to the point where the Tire can Delaminate or a Blowout can occur.
Speed Ratings can be somewhat arbitrary, because they are not required by Law, although most Manufacturers do test the Tires and display the results, in the form of a Letter Grade on the Sidewall. Here's a little better explanation of Tire Speed Ratings: (Source: NHTSA)
Speed Rating
The speed rating denotes the speed at which a tire is designed to be driven for extended periods of time. The ratings range from 99 miles per hour (mph) to 186 mph. These ratings are listed below.
Note: You may not find this information on all tires because it is not required by law.
Q 99 mph
H 130 mph
R 106 mph
V 149 mph
S 112 mph
W 168 mph
*
T 118 mph
Y 186 mph
*
U 124 mph
*For tires with a maximum speed capability over 149 mph, tire manufacturers
sometimes use the letters
ZR. For those with a maximum speed capability over 186 mph, tire manufacturers
always use the letters
ZR.
Hope this helps...
Happy Motoring!...Jim'99
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