I decided to do a bit of a reseaarch on that one too:
My tire is Bridgestone Turanza EL400; P215/60 R16
According to this web site:

http://www.tirerack.com/tires/Spec.j...=Turanza+EL400

this tire is 640 A/B (640 for treadware).
It seams like a better one for winter conditions.