BioWheels MTB Tech: Anatomy of Shiftsuck

June 27, 2008 on 10:52 am | In Uncategorized, Mountain | No Comments

Everyone with a mountain bike has heard of chainsuck…. how about shiftsuck?

Chainsuck can potentially stop you cold in your tracks. Excessively worn chainrings develop small burrs that effectively thicken the chainring - causing the chain to stick to theses areas and not release. The accumulation of mud on the chain and rings accentuate this condition. The suck part is your chain getting “sucked” up into your chainstay, either jamming or causing you to have to backpedal to get the chainring to release the chain.

A lesser known condition, Shiftsuck is chainsuck that occurs while downshifting from middle ring to granny, and can occur on brand-new drivetrains. Without sufficient clearance between chainrings and chainstays, shiftsuck can lead to your chain jamming into your bike’s chainstay - eventually leading to chainstay failure. Below are four photos showing the progression of shiftsuck. The first two show the underneath of the chainrings: in the photo the chainrings would be rotating backwards, and the chain is transitioning from the middle ring to granny gear.

Photo A: chain attempting to release middle ring and complete shift onto granny gear

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