More on Tubeless Tire Coming off the Rim in Étoile de Bessèges Stage 2 Sprint

Also, followups on thread direction, crank length, and chain waxing

Regarding last week’s post on another tubeless tire coming off the rim in a pro race:

Dear Lennard,

A couple of thoughts:

1) You make no distinction between hooked and hookless rims. I think the margin of error is much higher in this sort of situation with hooked. Whether it would have stayed on the wheel when the rim is as smashed as that one is unknown, but it seems it would have had a much higher chance of it. Personally I think the manufacturers’ move to hookless is irresponsible.

2) Something doesn’t jibe between the photo and the explanation—a rim with that big a crack would have lost air (& the tire) immediately. Maybe there was a smaller crack from the pothole, but that large crack had to be from when he hit the barriers.

John

Dear John,

Regarding your point #1, I agree that the likelihood of losing air out of a tubeless tire and then of subsequently losing the tire off the rim is greater with a hookless rim than with a hooked one. The fact that the maximum allowable pressure is less with a hookless rim than with a hooked one should make that point abundantly clear; there simply is less friction holding the tire beads and sidewalls on a hookless than with rim hooks.

However, once the tire beads have dislodged from the rim’s bead seat and have dropped down into the rim valley (as would have happened with Marc Brustenga’s rear tire when he veered in the sprint), it is equally easy for the beads to come over the rim walls since the height of the rim walls above the bead seats is the same with hooked as with hookless rims. The fact that a hooked rim has more friction against the tire sidewalls and the bead than a hookless rim is irrelevant once the tire beads have fallen into the rim valley; the amount of side force required for the beads lubricated with tire sealant to come over the rim walls will be minimally affected by hooks vs. hookless, since they are coming from the rim valley and not from against the rim walls.