I'm sure things are different under Brazilian law than US law, but in the US it's "treadwear" and the number is how long the tire lasts before it wears out compared to the "index" tire with a rating of 100. A typical all-season tire sold in the US will have a rating of 400-450, whereas a performance tire will often have a rating of 200 or less. That means the all-season tire would last twice as long as the performance tire and four times as long as the "reference" tire.
I don't know what the reference tire is rated at in Brazil, but generally you can expect your Goodyears to last a few thousand km less than your old Continentals would have, but not really a whole lot less.
