Comments on: Chain Suck: Causes and Fixes

By: Grant

Grant — Thu, 29 May 2008 23:10:02 +0000

“Does that answer your question?”

It does indeed. Thanks!

By: JoelGuelph

JoelGuelph — Thu, 29 May 2008 21:13:49 +0000

@Grant: As a chain wears out, it stretches so the pitch of the chain changes. So instead of being 1/2″ between links, it stretches to be slightly more than 1/2″. That slightly more than 1/2″ doesn’t match the 1/2″ spacing of the teeth on the rings and cogs, so the teeth wear down to match the new, slightly stretched pitch.
If you replace your chain before that stretch is too much, the teeth don’t wear down to match the chain. If you leave a stretched chain on, the teeth wear down so that when you put a new chain on with a 1/2″ pitch, the teeth no longer match the pitch. A new chain on worn rings and cogs will cause skipping and possibly chain suck.
The key is to replace the chain before the stretch becomes too much, and the general industry recommendation is 1/16″ of stretch over 12″. Since chains are 1/2″ pitch when they are new, you should get exactly 12″ when you measure 24 links. After time, when you measure 24 links, you will get a slightly longer measurement. I find it helps to have tension on the chain when measuring it to ensure you are measuring the full stretch. You can get tension by getting a friend to hold the rear brake and apply some pressure to the cranks while you take the measurement.

Does that answer your question?

By: Grant

Grant — Thu, 29 May 2008 17:35:44 +0000

I don’t understand why frequent old chain/new chain replacement cycles wouldn’t result in a prematurely worn out set of rings and cogs.

By: steve

steve — Wed, 28 May 2008 13:07:08 +0000

This may sound obvious, but don’t overlook a gummed up freehub body, too. Slow freewheeling will sag that chain bigtime, especially at higher speeds.

By: JoelGuelph

JoelGuelph — Tue, 27 May 2008 21:33:54 +0000

@198: I find it essential to know the technical information before diagnosing a problem, otherwise it is pure guess and check. I think the difference between frame designs is pretty much all down to the chainstay design around the BB and the length of the BB spindle. Chainsuck is unrelated to the frame, but whether or not the chain jams into the frame after sucking depends on the geometry of the chainstay where the rings are and how far the rings are from the frame.

@ALON: I think it really depends on the economics of your drivetrain and if you are getting chainsuck with a relatively new drivetrain or mostly when it is worn out.

You can find a tonne of “experts” that will tell you to replace your chain once it develops a 1/16″ of stretch over 12″, but I think it really depends on the quality and price of your components. Why replace a $30 chain 4 times to save a $30 casette and $20 chainring. You are better off letting the whole thing wear out and replace everything at once ($90 to save $50). If, however, you are replacing a $40 chain on a regular basis to save a $200 cassette and $80 cahinrings, that makes a lot of sense ($120 to save $280).

If chainsuck is a constant or common problem for you, it might be wiser to go with a) to reduce chainsuck. If you find that chainsuck happens primarily when your drivetrain is wearing out, it might be better to go with b) to save some cash. So, a) is the best “mechaincal” advice, but not necessarily the most cost effective.

By: ALON

ALON — Tue, 27 May 2008 19:13:28 +0000

So what is the best (mechanical) advise to prevent this problem?

Is it:

a) Replace the chain often, so the chain’s wear and stretch does not overly affect the chainrings

b) Replace the offending chainrings along with the chain (most likely not all the rings, maybe only #2)

This would be in addition to changing gears without too much load, not riding in crossover combinations and giving regular TLC to the chain and drivetrain in general (clean, lube, etc.)

By: 198

198 — Tue, 27 May 2008 11:47:32 +0000

Great article. It really helps to know the technical information behind the problem when you are trying to troubleshoot for solutions.

I have also found that certain frame designs are more prone to this problem then others.