Which size is better as well??

215/45/17
215/50/17
Thanks in advance

PS3 thread wear is actually 320, while F1 is 300. Advan DB I think is even higher. Advan Sport though is very low at only 180/240 depending on size. T1S is also only 180.

True that it's not 100% accurate but still a useful indicator.
It's like engine specifications as well, for example both the Lancer Evo & Impreza STI are rated at say 280HP but one is a bit faster than the other and yet still you can get a good indication of how much performance both of them capable of, which is surely way faster than an average 100-200hp sedan, but still much slower than a 500HP GTR.

actually no, for UTQG, which is printed/certified by the american DOT, they are tested by a uniform standard.
refer:
http://www.safercar.gov/Vehicle+Shoppers/Tires/Tires+Rating
http://www.tirerack.com/tires/tiretech/tec...e.jsp?techid=48

Unfortunately, the rating that is of the most interest to consumers is the one that appears to be the least consistent. While the Treadwear Grade was originally intended to be assigned purely scientifically, it has also become a marketing tool used by manufacturers to help position and promote their tires.

The problem with UTQG Treadwear Grades is that they are open to some interpretation on the part of the tire manufacturer because they are assigned after the tire has only experienced a little treadwear as it runs the 7,200 miles. This means that the tire manufacturers need to extrapolate their raw wear data when they are assigning Treadwear Grades, and that their grades can to some extent reflect how conservative or optimistic their marketing department is. Typically, comparing the Treadwear Grades of tire lines within a single brand is somewhat helpful, while attempting to compare the grades between different brands is not as helpful.

Unfortunately for all of the money spent to test, brand and label the tires sold in the United States, the Uniform Tire Quality Grade Standards have not fully met their original goal of clearly informing consumers about the capabilities of their tires. Maybe it's because tires are so complex and their uses can be so varied, that the grades don't always reflect their actual performance in real world use.

if course i read em, from the US gov site:
and from tire rack:

i too can quote selectively!

sure it can be inconsistent however it still can be used as a decent guideline which is what me/ 6UE5T is trying to find out.
unless of course tire makers are totally fine about getting fines. (pun totally not intentional)

that is of course provided consumers are fully aware of what they are getting into, such as good performance + good nvh = damn shit treadwear (due to very soft tires) and anything above 300 or so is very unrealistic figures that should not be trusted.

like i said, it's a mere guideline and consumers should also be self-informed by doing their own asking in forums/threads such as this, read up reviews from websites such as tirerack.

that's usually the norm before you buy something especially when they are not cheap such as good tires, no?