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For the health of your bicycle it is very important that the chain-rings, chain and cogs are serviced or replaced regularly. The chain is really the main topic of discussion here as it wears more quickly than the larger and more durable chain-rings on the crank-set, or the cogs in the rear cassette. As the chain wears, the rollers or unions between the links gradually lose their cylindrical shape and take on the appearance of an hourglass, with a narrow waist where they engage the cogs and chain-rings. If you look at a very well-worn chain, it can be millimeters longer over its entire length than a new one. Either condition leads to accelerated cog and chain-ring wear, as well as hindering shifting and efficiency. This is what you want to avoid.
How often should you replace your chain? Some recommendations call for mileage intervals, i.e. every 2,000 miles, but this can be misleading. Chains will wear more quickly for riders who often encounter large hills or heavy weather, while identical mileage over flat terrain in pleasant weather will cause little apparent chain wear. Similarly, 2,000 miles for a 105lb woman will wear a drive-train much more slowly than the same parts under a 195lb gentleman. Put simply, we suggest you judiciously keep on eye on your chain, or seek the advice of a good mechanic.
Chain wear can be measured. With an ordinary 12’ ruler, measure from one link pin, down to the 12” mark. Since each link pin is 1/2” from the next, a new chain’s 24th link pin should fall exactly at 12”. When the 24th pin does not line up exactly with your ruler’s 12” mark, it’s time to replace your chain. There are"chain checker” devices sold at bike shops as well that help you evaluate chain wear more easily. This way you have a more definitive way of determining the mileage you can expect from your chain in your area, with your stature, the quality of your bicycle and its parts.
Chain wear is often referred to a “stretch”. Technically, what’s really going on is that the chain’s pins have worn slightly at each link. Each worn pin allows the chain’s rollers to displace slightly, like the cardboard tube inside a roll of toilet paper. The resulting slop allows each link to offset forward of where it should be, especially under the tension of hard pedaling, where a “stretched” can cause a violent and disturbing skip or clunk, when the roller is so poorly aligned with your cog that it cannot drop between your cog’s teeth. This causes the next chain roller to drop into the intended slot, and the teeth in your mouth, having been rather jarred by the experience, will ask you to please take your bike to the shop for a new chain, and possibly a new cassette if you’ve let it get to this point!
Chain-ring and cog wear is much more difficult to diagnose than chain wear, especially with the positionally-specific shaped cog and chain-ring teeth that are integral with all modern derailleur drive-train systems. Keeping a good chain on your bike, and making sure it is clean and well-lubricated will ensure that you get the maximum life from your chain-rings and cogs. Your cogs and chain-rings should last through three to five chain replacements, perhaps more. If you notice excessive friction or reduced shifting performance after a chain replacement, it is probably time to replace your chain-rings and/or cogs. When replacing these items, we strongly recommended that you stick with original manufacturer replacement parts whenever possible.