Mark J. wrote:

I'm guessing you mean a brake /cable/ runs
under your top tube. ("Cable" is the common
term for brake and derailleur-control wires.)

If the washers are soft and rubbery, vaguely
doughnut/torus shaped, yes, these are
commonly used to keep cable from rattling.
If the length of exposed cable is long, it
doesn't take so very much bouncing of the
bike to get the cable to bounce against the
frame tubes. Brake cables aren't all
that stiff.

Great, thanks!

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