Chain measurement the dark art

Kingsmill1

I'm looking to replace my chain on my allez sport as its stretched I'm going for a direct replacement which is a kmc x9 chain now the next bit is how can I insure I measure it correctly and not totally bugger the job up. Can I just measure off the old chain or would this cause problems as its stretched a little. I'm a total bike mechanic novice so please excuse the dumb question but want to learn how to do it myself rather than pay £8 a time to my lbs.

16mm

Just measure against your current chain. You want the same number of links, but you old one won't be so stretched that you can't measure side by side.

Mad_Malx

... so lie them down next to each other (on something clean) and kink the old one slightly so that the links stay roughly aligned.

Edit - and make sure you have the outside link at one end and end up with an inside link at the other.

sungod

before you remove the old chain, use a 12 inch ruler and measure the distance from one of the pins to the pin that will now be slightly past the 12 inch mark - see how here... http://sheldonbrown.com/chains.html

if it's less than 1/16" past the mark, chain is ok

if it's reached 1/16" but is still less than 1/8" past, it's time to change the chain

if it's 1/8" or beyond then the old chain has worn so far that it has probably damaged the cassette, in this case you'll find a new chain may slip on the old cassette or you'll get accelerated chain wear - if the chain has reached this point, you may as well run it a while longer because when you change it you'll need to change the casssette (which costs a lot more)

moral - check the chain every few weeks, otherwise the cassette may be worn out much sooner than it should be

damov2

It's as simple as counting the pitches, just count each pin (pitch) do the same for the new chain and your sorted.

Kingsmill1

Thanks for the advice I got a kmc chain checker off flee bay chain is still ok for the moment

simon_e

damov2 wrote:

It's as simple as counting the pitches, just count each pin (pitch) do the same for the new chain and your sorted.

Yes - count pins, don't measure.

As for wear, I would err on the side of caution and change it sooner rather than later.