So, what I'm familiar with when it comes to tire sizes is apparently quite different than you folks. For example, my M3 has 18" wheels - 225/45R18 in the front and 255/40R18 in the rear. Now, I look at the wheels/tires on what you folks are driving and you're talking about 31s, 33s, 35s, etc. Obviously this isn't the rim size, which is what I'm used to. I assume this is the radius of the tire?