Originally Posted by dddd

Those narrow, raised areas that run out to the rim sidewalls are the bead seat shoulders.

The shoulders are supposed to be of a very precise diameter, such as to take up any slack that might otherwise allow the tire's beads to lift up, and at some pressure climb over the top edges of the rim sidewalls.


it's very important that the tire's indicator line be at a uniform distance above the rim sidewall early in the inflation process.
If the indicator line rises up in one spot during inflation to higher pressures, then the rim's bead shoulder diameter is insufficient to control the pressure, and the inflation pressure will be limited to some pressure under the pressure where the bead starts lifting up.
Only an increased shoulder diameter or bead hook can retain the tire at higher pressures.