Yeah, my friend had 2 of those bulges on one tire next to each other, and one on the other. She hit a lot of curbs. Needed new tires because of it, but she had a $hitty car. Needless to say she had a blowout in a busy part of Saginaw...

 

when they pull it off the rim, check it for patches. Bet it has one.

 

I'm just looking at a picture, but yes, that looks like where the tire hit a hard edge-- a pothole, curb, or other. The symptom, as I see it, is that the impact bent the metal bead of the tire inward at the impact point, thus causing the area around it to bend out. Since that bead is metal, it doesn't like to bend, and definitely doesn't bend back. And because the belts are tied to that bead on most tires, they're following the new non-round path, thus causing the bulge.

Chalk it up to "the cost of owning a car" and buy a new set of tires.. you can get away with swapping the front pair with another brand, but don't just swap in one unless you're going with a matching OEM, and even then, not if you've got a lot of miles on the other tire.

 

Well, I am getting a new set of tires. The shop said it definitely looked like an impact spot; I still am not sure that I hit anything that would warrant that damage but what are ya gonna do. Got a very good deal on General Exclaim tires through discount tire (they price matched treadepot.com, who was $10/tire less than tire rack) and I even got a few bucks credited for the two rear tires that are about 1/2 worn. The tires should be in in a day or two, and installed Saturday.

 

A defective tire will have a knot/bulge on the inside AND outside.....i.e., the cords have failed......knot/bulge on either the outer sidewall or the inner sidewall indicates impact damage.....the tear....it's a cut/tear that occurred when the rubber bottomed onto the rim edge....... beats me how the rim wasn't damaged...... hopefully the tire guys gave it a real good eye ballin'!