Get Your Chain Checked for Stretch.

In the good old days, the better 8-speed chains would, with good maintenance, occasionally last 7000 miles or more. The narrower 9 speed chains do well to last over 1500 miles. It is not uncommon for the newest 10 speed chains to stretch to their maximum useful life in as little as 800 miles. A stretched chain is not going up in flames if you continue to use it, but, because there is now a greater distance from chain pin to chain pin, the chain will wear an elongated and—when matched with a new chain—unusable pattern into the cogs and chainrings (see picture below).

On mountain bikes with the new ultra wide range of gears on the rear wheel, many riders stay in the middle chainring nearly all of the time. Luke! Use the little ring! Running one ring most of the time means that it wears out much sooner than the unused ones!

The three rings have overlapping gear ratios, so, if you are on the middle ring and one of the innermost cogs, shift down to the small ring and one or two cogs smaller in the rear. The result is that you will have the same gear ratio, meaning the same effort and cadence, but in a kinder and gentler combination. Again, if the cogs or chainrings are worn, you won‟t find out until you have to install that new chain with the original length from pin to pin. The new crisp chain will “skip” on a set of teeth that have had the notch between them elongated by a stretched chain. Rear cogs that are worn will give the rider little „popcorn‟ pops or skips as the chain releases, but catches on again quickly. Chainrings that are worn will result in chain skips that feel like the bottom dropping out of your pedaling world.

Below are two videos of the chain being measured. You will notice that the new chain still has some swing to the measuring too. The stretched chain will allow the tool to swing the full distance. The second chain is at the right time to replace. If the chain tool makes its full swing easily, or if the tool still has some room after the full swing, then the new chain is likely to skip on the current cogs.

New Chain

Worn Chain

On mountain bikes with the new ultra wide range of gears on the rear, many riders stay in the middle chainring nearly all of the time. Luke! Use the little ring! Running one ring most of the time means that it wears out much more rapidly than the unused ones. The three rings have overlapping gear ratios, so, if you are on the middle ring and one of the innermost cogs, shift down to the small ring and one or two cogs smaller in the rear. The result is that you will have the same gear ratio, meaning the same effort and cadence, but in a kinder and gentler combination. There actually is a perceptible reduction of effort due to the reduced friction of the chain bending less from chainring to rear cog. Again, if the cogs or chainrings are worn, you won‟t find out until you have to install that new chain with the original length from roller to roller. The new crisp chain will “skip” on a set of teeth that have had the channel between them elongated by a stretched chain. Rear cogs that are worn will give the rider little „popcorn‟ pops or skips as the chain releases, but catches on again quickly. Chainrings that are worn will result in chain skips that feel like the bottom dropping out of your pedaling world. The bottom line is, chains are cheap compared to cogsets and chainrings. Measure often and replace if in doubt. The new Shimano Dura-Ace 10-speed cassette is around $200. You can get three or more chain lives for one cogset.

The worn chainrings are also the reason that “chain-suck” happens. Notice in the picture below the flaring at the leading edge of the teeth. When the front derailleur shifts to a smaller chain ring there typically is a bounce to the lower chain path and the bouncing chain can snag on the flared tooth and get pulled up into the frame's chainstay. The only reliable solution is to replace the chainring.