It is not uncommon to find creases, ripples, valleys or waves of indentations on the sidewall of your radial tires. On smaller tires, they can sometimes be very delicate and easy to miss. On larger tires, they might stand out and be quite obvious, even from a distance.
These creases are known in the tire business as sidewall undulations. Sidewall undulations are vertical, meaning they make a straight line across the sidewall, from the bead to the tread. They develop naturally because of the internal architecture of your radial tires.
Sidewall undulations will not compromise the performance of your tire. They are only a cosmetic tire characteristic. However, as always when you find something out of the ordinary on your tire, please ask a tire professional to take a look to make sure your tire does indeed have a normal tire undulation and not a dangerous bulge.
Sidewall undulation occurs naturally on radial tires because of the way they are constructed. Just inside the outer walls of your radial tire, it is wrapped with sturdy fabric cords to reinforce its strength. The more strength needed for your particular tire, the more layers there will be of the fabric cords (or ply) .
Those cords are generally wrapped directly up and down vertically over the sidewall, not across it at an angle. Because of that construction, you can sometimes see the sidewall ripples where the rubber compound presses tightly against the thin vertical spaces between the tightly wrapped ply cords.
The bigger the tire and the more ply that it has, the more likely you will notice the sidewall undulation, much like the “six-pack” of a body builder. That’s because larger tires have taller sidewalls, which means longer undulation ripples, more inflation pressure to push the rubber against the ply, and probably more weight on the tires, which also increases the pressure.