Re: Fine Tuning Shifting

On Thu, 25 Jul 2024 19:58:53 GMT, Tom Kunich <cyclintom@yahoo.com>
wrote:

I have a continuing problem with the shifting goin out of adustment. In one case the right shifter wire partially broke from my over-tightening it but in the other three cases I've had to mark it down to cable stretch which Andrew says doesn't exist. But the wires did not move and the shifting moved towards shifting into a faster gear. I can only assume that wire layup tightened up a little and showing those symptom.>

1.2mm galvanized cable (shifter cable):
120 kg  (265 lbs) min breaking load.

1.6mm galvanized cable (brake cable):
220kg (485 lbs ) min breaking load.

<https://en.wikipedia.org/wiki/Working_load_limit>
I don't know the safety factor, but my guess(tm) is about 5 for the
brakes.  That puts the maximum load for the brake cable at:
   485 lb / 5 = 97 lbs

I don't know what you're using for a shifter or brake level.  The
mechanical advantage can't be much.  This covers brake lever
mechanical advantage, but not shifter:
<https://www.toolonpyora.fi/post/mysteries-of-the-cantilever-brake-what-about-the-brake-levers>
For brakes, my guess is no more than 37 lbs with a mechanical
advantage of about 6.  Therefore, with a strong grip, you might be
able to tension the cable to:
  6 * 37 lbs = 222 lbs

We lose grip strenth as we get older.  For 65+, the typical RH grip
strength is more like 21 lbs
<https://godsofgrip.com/pages/average-hand-grip-strength>
  6 * 21 lbs = 126 lbs

The shifters will be very different numbers, but I don't have enough
info handy to work those out.

Pulling on the brake cable with 126 - 222 lbs is more than the 97 lbs
required for the minimum breaking load.

<https://testbook.com/physics/stress-strain-curve>
--
Jeff Liebermann                 jeffl@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann      AE6KS    831-336-2558