I'm unsure what the "treadwear" number refers to, other than it appears that the higher the number the better the tread life. But I'm unsure that is correct.
Treadwear rating is supposedly a percentage life compared to the 100-rating. So a 400 would last twice as long as a 200. But I can't remember is that is actually the basis, just how I remember it. And I'm sure it's more of a guideline than a hard fact but I believe it is a government standard.
That's correct, and its inclusion and the procedure for calculating it are indeed government standards. However, each tire manufacturer uses one of its tires as a "baseline" tire from which the calculations are made, so the numbers can vary from one make to another. Also, it's really not precise at all; as they say, YMMV (your mileage may vary). I know one manufacturer that changed the rating on one of its tires without any changes whatsoever to the tire itself. As a general rule, though, you'll find that R-compound track tires (typically with treadwear ratings of 100 or less, or none at all) give you fewer miles than extreme performance summer tires (typically 140-200), which give you fewer miles than maximum performance summer tires and ultra-high performance summer tires (both typically 250-350), which give you fewer miles than all-season tires (typically 400-600 or more).
Oh, I'm also unsure on Class. What does XPS mean? I figured out that UHPAS means Ultra High Performance All Season. But does that mean that UHPS means Ultra High Performance Season? And if so, which season, winter or summer?
These are the performance categories as determined by the Tire Rack; you can see the list of categories, along with brief descriptions, on their website
here.
Incidentally, I would not recommend any all-season or winter tire on an NSX unless it is regularly driven in snow or below-freezing temperatures. Those types of tires are designed for colder temperatures and performance is compromised in warmer temperatures, compared to summer tires.
Also, I don't know how to interpret the "section width" column.
It's the spec that tells how wide the tire is at its widest (at the "bulge"), when mounted on a specified width of wheel (the "approved rim width"). You can ignore it for purposes of selecting tires. Just go with the nominal tire size (e.g. 215/40-17), in which the width is the width of the tread, not the section width.
Again, for an NSX with stock 2002-2005 wheels, if you're looking for a bit better treadlife than the "extreme performance" tires, I'd get the Kumho Ecsta LE Sport, in the stock sizes 215/40-17 and 255/40-17.
