Stretching of Tubeless Tire Beads

Plus more on aging tires and cables breaking inside Shimano STI road levers

Dear Lennard,

To the best of your knowledge, do tubeless tire beads stretch over time with repeated mounting/dismounting?

I'm building a new climbing wheelset with aluminum nipples. To reduce the possibility of rounding the nipple flats while I turn the alloy nipples, I am finalizing spoke tension and wheel true with the tire mounted and pressurized to lower the spoke tension

After each round of nipple turns, I dismount the tire to get accurate spoke tension.

Am I increasing the likelihood of a tire blowing off the rim by repeatedly stretching the tire bead when I mount and dismount the tire?
―Carl

Dear Carl,

I ran your question by some tire manufacturers. Here are some answers to it from Pirelli and Challenge. They both agree that tubeless tires stretch from prolonged inflation and are not in agreement about whether they also stretch from mounting. Whether the stretch is enough to increase the likelihood of the tire blowing off is subject to debate.

― Lennard

From Pirelli:

Good question. The bead is a textile, so depending on how it is manufactured (more or less torqued, pre-stretched, resin dipped or not, number of rounds, the elongation value of the raw fiber itself… there are a few variables that come into play) can suffer more or less from being stretched over time or over multiple mounting procedures.

On average, the boundaries are from “it suffers very little” to “it suffers close to nothing”, so we are speaking of a minor factor here.

BUT, still existing, and relevant to some degree: the biggest variable is how it is mounted and stretched during the mounting procedure and the more fatigue it endures based on how much strength I need to apply to pull it over the rim shoulder (for example, if I need more than one tire lever, and I need to push hard to get it over, that is a sign that I am putting a lot of stress and fatigue into the bead itself).