On Aug 22, 9:55*pm, DougC wrote:
On 8/22/2011 3:32 PM, thirty-six wrote:



On Aug 22, 9:28 pm, *wrote:
On 8/22/2011 1:18 PM, thirty-six wrote:

The wire stiffens the connection with the rim so that the tyre stays
in place. *The wire's strength is of no particular importance, it's
the resistance to bending which is key. *...

I don't know if I believe that.

It would mean that you could take a clincher tire and cut both beads
completely through--and then mount& *inflate it and still have it stay
on the rim, with just as much pressure as with the beads uncut.

You would be breaking the beam and so the hold of the tyre is
compromised around the cut. * Test it statically. *Do not ride it at
speed.

Obviously the beads are placed under great tension in use, since for
~100 years steel was the only material used and in the last several
decades the only other material used has been kevlar (which is also a
high tensile strength material).

The steel wire is used as a beam for the tyre's unfortunate edge. *The
tubular tyre does not of course suffer from this liability as the
edges are joined together making the tyre essentially edgeless.

You need to sort the terminology you're using.

Stiffness = resistance to bending.
Tensile strength = resistance to a longitudinal pulling force.

Bicycle tire beads do not need to be stiff at all, steel is stiff but
[foldable] kevlar is not, and both obviously work.

I've explained why.