You should never set your tires below what the door says, unless aftermarket wheels and tires are used. The door plackard is always right, and manuals have been known to be wrong in all brands of cars, due to companies using the same manuals for several cars in their lineup with only different covers.
The reason is that the tires are tested at a certain speed (see below)for a period of 1 hour at the set psi at a specified load. When the tire is tested with less than optimal psi, it will not last nearly as long or the high speed. AKA crash and burn.
speed rating speed
H 130mph
v 149mph
w 168mph
y 186mph W,Y,(Y) are all under the Z rating

186mph and up:rofl:
There are several other speed ratings, but I just put down the ones related to the new GTO, I believe stock is a v rated tire.
You can set your psi higher to carry more weight, but do not set above 40 or 45, whichever is max psi. +1psi=+40lbs approximately.
Sorry for going technical again, but I hope it gives you guys better understanding
