Howdy. I replaced my chain just this morning, so the topic is fresh on my brain. You cannot assume the measurement of your old chain is correct, so based on your drivetrain, there are some easy and common rules to apply. What brand is your drivetrain? SRAM is super easy, and Campy and Shimano are fairly simple as well. A general rule of thumb is to first remove the old chain, then wrap the new chain around the largest chainring up front, and the largest cog in back without feeding the chain through the derailleur. Make the chain tight, then add two, sometimes three links to this distance, and this will be a good length. Let me know if this helps or you have any other questions. I by no means am a professional mechanic, but I'm somewhat mechanically inclined and have never had chain or drivetrain issues. Good luck,

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Zach's blog

Zach's method was one way which a lot of folks use. I have a different way that i find is easier. I wrap the chain around the smallest c-ring and smallest cog. Feed it thru your deraileur pulleys and then pull the 2 chain ends together. Now comes the tricky part. What we use in our shop most of the time is a broken spoke that we have bent into a "chain holder" but you can use anything or nothing. Pull the chain so that your bottom chain line sits just off the exposed chain wrapped around the top pulley wheel. Then you cut the chain so that you can use the proper connector, i.e. sram link, shimano pin, campy links and reconnect the chain.

It's really pretty simple and isn't a big deal. The only time you may have to look into more that just the chain is if you have put an excessive amount of miles on your cassette. If in that case you might need to replace the cassette at the same time as the chain or you could "slip gears".

Hope that helps.
Brian

Yeah, and what he said too ;) That's good info, and I'll try that one next time too. Tanks mon,

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Zach's blog

Is there any risk to having the chain a link or two too long/short?

What difference in riding will I notice with a poorly fit chain?

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Proud Member of the Cervelo Mafia.

Below is the link to Park Tools site. They give 3 different methods to figure how long your chain should be.

If your chain is too long, it will sag and actually slap a little when tension is off. Your shifting will be pretty sloppy. Also, if it's long enough, it can jump right off causing more damage. A short chain will make it hard for you to pedal, and cause extra wear on your cogs and chain ring.


http://www.parktool.com/.../readhowto.asp?id=26

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Slowguy

(insert pithy phrase here...)

http://www.youtube.com/watch?v=lyn7fxHDV-M

A lot of times we purposely cut the chains to long for our mountain bike racers. It allows them to be able to run gears in their big c-ring more fluid w/o high chain tension. But on road bikes you are better off to cut it to the proper length.

If I am replacing a correctly fitting Shimano chain with another Shimano chain, can I just count the links on the old one and cut the new one to the same length?

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Proud Member of the Cervelo Mafia.