i noticed this a while ago. all of the tires in the tire walls at vir are brand new. not old used race tires, but brand new tires. they drilled holes in them and bolted them together too. there must be thousands of them.
At NHIS the tire walls are made of used Indy Car tires. The last Indy race there was kind of a long time ago (i think), so the tires are a little stiff these days. I don't recommend testing them; just take my word for it.