Tire "undulation", now that was a new one on me.
I purchased a new set of Mastercraft Courser HTR LT245/75R16 10E tires for my TV two years ago, and shortly thereafter noticed what looked like narrow indentations on the outer sidewalls (all 4 tires). I was told by my tire dealer this was normal/common and was the result of the tread bonding process..., if it was a "bulge" then that would be considered a problem.
Anyway, the tires have preformed great to-date.., but I decided to "google" the sidewall indentations for my own curiosity today (detailed the tires yesterday and got me wondering again).
Here is what I found: "Sidewall undulation is an indentation on the sidewall surface of an inflated tire. Undulation is common in almost all radial tires and is most visible on tires with larger sidewalls or tires running at a high inflation pressure.
In a radial tire, the body ply cords run parallel to each other across the tire from bead to bead. With the straight across construction, the joining of the ply material in the sidewall can cause a slight indentation or wavy appearance on the sidewall surface of the tire when it’s inflated.
Tires with sidewall undulation are safe to use on your automobile. The undulation will not affect vehicle performance and will not increase your risk of a blowout or tire failure."
I found pretty much the same information at a number of different sources.
So now I know.