2-Ring Suck : Chain-Bridge Mechanism

A more extreme mechanism unique to 2-ring suck can also occur if the mismatch in cross-over distance is greater (say 3.15" distance for 3.00" of chain length). The chain now not only loads the pressure-face of the dispatching tooth, but it also loads the trailing-face on the receiving tooth - sometimes called a "Chain-Bridge".

So the chain becomes "locked" between the dispatching tooth from which it won't disengage, and the receiving ring upon the trailing tooth-face of which it is "wedged" down by the full tension loading in the chain. This can occur even if there is little pedalling load on the chain, and has probably happened to most cyclists at some time, especially if the chain was a bit dry ; its often called a "mis-shift" - being actually 2-ring suck - and occurring when the chain is transferred at an unfavourable position for relative tooth alignment and crank cycle loading.

If the chain-ring material is not tough enough, small failure indentations (dimples) can occur in the metal of the dispatching tooth's pressure face and the receiving tooth's trailing face ; this will increase the future incidence of the problem.

Copyright Jonathan Levy, 2000. All rights reserved.