Join Date: Mar 2005
Location: SF Bay Area, California
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Originally Posted by shane45
What is chain authority anyway?
Ok, it's like this:
Think of the derailleur cage as a second-class lever arm. The pivot end of the arm is the fulcrum. The tensioner spring applies resistance (chain tension) right next to the pivot.
With a long cage derailleur, you've got yourself a long lever arm.
With a short cage derailleur, you've got yourself a short lever arm.
In either case, the tensioner spring is the same, applying the same resistive force to the arm.
You can look at this two ways:
(1) In the case of the long cage, the chain needs to apply less force to the cage (lever arm) to displace the spring. Hit bump, momentum causes chain to move upward against the cage (lever arm), displacing resistance (tensioner spring), allowing chain to hit chainstay. clack clack clack
(2) Imagine playing Whack-a-Mole
with two different length sticks. Shorter stick (short cage derailleur) allows you (tensioner spring) to go nuts on the moles (chain) and put them in their place. Longer stick (long cage derailleur) is a little more unwieldy, doesn't let you bang them with as much force, and will get deflected more easily if you don't score a direct hit. About the only thing the longer stick has going for it is its longer reach, and if you have a lot of moles to whack (or a lot of chain links to manage), this extra capacity might prove adventageous compared to a more powerful short stick.
Not a perfect analogy, but I think it works.