A cyclist thinking about chain wear.

Probably one of the most quietly contentious discussions in cycling is chain wear.

(Other areas of contention, such as chain lubrication and doping in the pro peloton are more contentious, but not nearly so quiet.)

In an attempt to limit my written meanderings to those areas where I can provide more light than heat, I offer answers to some common questions about chain wear.

Q: What is "chain stretch"?

A: A very inaccurate term for a common issue.  Chains to not "stretch", at least not in the same way that Lycra does.  They do, however, elongate, or change functional dimension, as a result of wear.

In a modern bicycle chain, there are two places that wear occurs:

1. Between the side plates and the pins.
2. Between the rollers and the "shoulder" on the side plate that they ride on.  (In older chains, the roller rides on the pin.  However, in every modern chain I've seen, the roller rides on shoulders formed on the inner side plates.)

As the side plates pivot around the pin, there is wear between the side plate and the pin.  This wear enlarges the hole in the side plate, and reduces the diameter of the pin. This creates an effectively "longer" chain.

As the roller pivots around the pin, it wears on the side plates, allowing slop in the roller's position.

These two factors cause the chain to mesh with the chainrings and rear cog(s) less precisely. Less precision means that the load on the chain is borne by fewer teeth, increasing the wear on the chainrings and rear cog(s).

Chains are relatively inexpensive, chainrings and rear cassettes are relatively expensive, so it is worthwhile to replace the chain early.

Q: How do you know when a chain is worn out?

A: There are a few different tests:

• Use a good ruler. Measure 12" from the center of a pin on the chain. If the center of the pin 12" away is past the 12" mark, you have measurable chain wear. I replace chains at 1/16". If it's a 5,6,7,8 or 9 speed chain (if in doubt, count the rear cogs) you can go a little further.
• Use a chain wear gauge. Use a gauge that is intended for the number of rear cogs. (Past 9 speeds, the chains start getting significantly narrower, as do the cogs, making the wear more of an issue.) There are 2 tests on the gauge;
• the first (usually marked .05) means that you can reasonably replace the chain,
• the second (marked .75 or 1.0, depending on the type of chain it's meant for) means that the chain is done, finis, kaput. You can keep riding it, but be ready to replace the cassette along with the chain, and maybe the chainrings.
• Abbey Bike tools makes a chainwear gauge that uses a different approach, but if you are far enough into bicycle tech to buy a $45 gauge, you probably don't need this article!
  
• Shift into the big ring, grasp the chain where it wraps around the front of the chain, and see if you can pull the chain away from the ring. If you can discern movement, you are looking at replacing the chain. If you see light between the link and the chainring, look at replacing the cassette as well.

Q: What about just running the whole drivetrain until it's absolutely toast, then replace the whole thing? 

A: People do that, and some claim that it's a wash (higher cost, but less frequent). I admit, I'm picky about shifting quality, and a worn chain (and worn cassette) don't shift as well. It's also a PITA when you're on a long tour and you have to source replacement parts. (Ask me about replacing cleats in the middle of South Dakota sometime.)

Q: How do I minimize chain wear?

A: Keep the chain clean. 

• Wipe it down after a long ride, or once a week if you do a lot of short rides. 
• Periodically take the chain off the bike and give it a thorough cleaning in a solvent bath or ultrasonic cleaner. (I'm picky, I do both.  Water based degreaser in an ultrasonic bath, followed by agitation in denatured alcohol, which does double duty in getting the last remnants of gunk out and in getting the water out.)
• Use fenders. Most of the damaging crud that hits a chain from the outside is thrown onto the front chainring by the front wheel. I have fenders on my "daily driver" bike.

    Use a good (i.e. appropriate to the use) lubricant. This is a very contentious issue among cyclists, but here are the broad categories with some guidance for their use:

• Oil-Based. TriFlow, Boeshield T-9, any lubricant that is called a "wet" lubricant.
• Best choice for dealing with wet / rainy conditions. 
• Downside is that the oil will tend to hold dust and dirt, so not so good for dusty conditions. 
• The worst thing you can do here is use too much. Apply a drop to each roller, let it sit for 15 minutes, wipe off any excess with a dry rag.
  
• Dry Lubricants. Generally either described as "dry", the Rock 'n Roll brand is common. 
• These have a solvent with a wax or other dry lubricant in suspension. The solvent evaporates, leaving the lubricant behind. 
• Great and convenient for dry conditions, and often serve to clean the chain in the application process. (Read the directions.)
  
• Often require you to wait overnight between lubing and riding. 
• Can get expensive.
  
•  Wax
• Involves completely stripping any existing lubricant off the chain and immersing the chain in melted wax.
• Definitely holds the least dirt and grit, and often has the lowest friction.
• Downside is that it is a hassle, and has to be redone as often as every 200 miles. For me, that would mean doing it at least every week on-season. (I'm anal about chain wear, but not that anal.)
  

I use Boeshield T-9 on my endurance events bike and my daily driver, both of which see getting caught in the rain. I use a Dry Lubricant (Rock 'n Roll Extreme Dry) on the bike that sits on the indoor trainer. It not only never sees rain, but the dry lubricant keeps the trainer and the floor cleaner.