Think of it like a one string guitar and the cable stops as frets. The only thing that will cause a change in the pitch of a string/cable is a change in tension or a change in vibrating length. Since the vibrating length of the cable between the two stops is unchanging, any change in pitch has to be attributed to a change in tension, and the only way to increase the tension of a string or cable is to elongate it. What happens to the cable beyond the stops or in the housing is of no consequence, unless movement somehow changes the vibrating length.
Kevin Ko Eugene, OR USA
-----Original Message----- From: Andrew R Stewart [mailto:onetenth@earthlink.net] Sent: Wednesday, January 05, 2011 12:55 PM To: KO Kevin; classicrendezvous@bikelist.org Subject: Re: [CR] Brakes and Flex
Kevin- I do very much like using non instrumented methods to test theories. But a few points about your suggestion. It might be hard to localize the cable tension increase from any lever or tube stop flex (especially lever movement or flex). Second, with the cable effectively touching the casing/stops at the entry/exit points wouldn't that tend to just dampen the cable in housing portion of the tonal changes. Third, couldn't the same be done for the housing? (Although it might not have much "ring" to it's being plucked, it's tension will definitely be different under tension). Seems to me that your experiment has too much "noise" in it (sorry but couldn't help making that pun).
> Elastic stretching of the brake cable is easy enough to verify or refute
> for those of you who have a bike with a length of exposed cable along the
> top tube. Take up the slack by moderately squeezing the brake lever.
> Then start plucking the cable like a guitar string as you increase the
> force on the brake lever. As a guitar player and builder, we know that
> you cannot increase the pitch of a string without either shortening it or
> elongating it to increase the tension. So, if the pitch of the brake
> cable increases as you squeeze the brake lever, the tension of the cable
> is increasing and the cable is stretching. If the frequency doesn't
> change, the "stretch" is in the housing, shoes, calipers, etc.
>
> Kevin Ko
> Eugene, OR USA
>
>
>
> _______________________________________________
Andrew R Stewart
Rochester, NY