Originally Posted by
sunburst
I know this is an old thread, but it popped up when I was searching for something else (does search ever work right at BF?).
Anyway, my son just bought some Hed wheels with the C2 Plus rims: 25mm ext, 21mm internal width.
He mounted 23mm on these wheels which are way out of the recommended range of these charts. But I talked to Hed first. They said these rims were designed around 23mm tires - surprise, surprise. And when I mount tires on these rims, they seem to "pop" on somewhere north of 70+ psi, with a very positive connection. My guess is Hed has a different hook design for the bead to latch onto, to accommodate tubeless tires. I do not think these narrow tires are going to blow off these wide rims.
No real reason to post all this, but it is interesting to me.
In the days before tubeless-ready rims, bead seat diameters were more of a suggestion than a requirement -- rim diameters might be slightly "big" to try to prevent blowoffs at high pressure, or slightly "small" to make tire mounting easier (and that's assuming rims didn't vary in either direction due to poor QC.) With tubeless rims, manufacturers are finally making rims with consistent bead seats that support the tires where they mount, which goes a long way toward preventing blowoff. (In fact, some carbon clinchers don't even have or need hooked sidewalls!) And with a consistent BSD, there is less need to use a large major diameter, so excessively-tight combinations should be rare, too.
