Getting Rid of 2-Ring Suck
Copyright © Jonathan Levy, 2000. All rights reserved.
For 2-ring suck, one or more of the following eight options may be needed to resolve any mismatch in tooth/chain pitch across adjacent chain-rings. Obviously, you must first check that there is no damage to the rings, teeth or chain, and remedy these if necessary.
The following simple option is often successful :
Replace any aluminium (or die-pressed powder-alloy) granny-ring with a strong, hard, and tough steel. This is the primary solution for 1-ring suck. Often it will also resolve 2-ring suck, probably because the different rotational alignment of teeth and tooth shape on the new ring fixes these problems without it being explicitly apparent.
The next four options can be used individually or in combination to adjust the rotational alignment of teeth on adjacent rings ; this will improve matters if the change is in the right direction, but may worsen matters if it is not.
Install a different granny ring and/or middle ring, with different tooth shape and/or with different alignment of teeth along its circumference
Install a ring with a different number of teeth, to change the tooth-ratio of adjacent rings, and hence the relative alignment of teeth
Rotate the fastening position of the chain-ring by one or more bolt-holes, which will change the relative alignment of teeth.
Adjust the adjacent granny/middle rings so that the small amount of play which exists in their bolt-holes is used to fasten the rings at that extreme of play which reduces problems
Sometimes this measure can help :
If the problem is seen to occur regularly on the same teeth, there may be a
dimple or indentation
in the trailing face of one or more receiving teeth ; getting rid of this will help temporarily, but for a longer term solution, the fundamental problem of pitch mismatch across rings must also be resolved. Similarly, there may be dimples/indentations in the pressure-faces of dispatching teeth. File affected tooth faces to eliminate the dimples in a manner similar to that described in Filing Tooth Profiles.
For a set of new chain-rings or where the the problem just cannot be resolved by any of the above measures :
It may be necessary to get a different make/design for the complete set of chain-rings ; as a consequence, this, in turn, may require a different set of cranks ; it is advisable to get a well matched set, with tooth ratios and tooth shaping/ramping generally known not to suffer this problem, and from a single manufacturer.
In all cases, it is worth developing the following habit :
Reduce pressure on the pedals whenever changing gear, to reduce the driving forces of, and hence the opportunity for, this type of chain-suck. Only once the chain has changed fully to the receiving chain-ring, should pressure be re-applied to the pedals.