How do I work out what size my chain should be ???

[deano69]

I would like help please on a good guide on how to size the chain lenth I need ?
I have checked out many online guides but still unsure as the one where you work out your largest front rings teeth eg 42 then largest cassette ring eg 32 then add chain stay length which is 43cm from crank centre to rear wheel axel centre then press calculate which gives me 137.16cm or 54 links....I tried this but when chain on largest front ring and largest rear sprocket derailleur cage is pointing forward under full stretch and strain but works perfect on other 2 front rings ?

I think 1 more link added will be ok but when its on smallest front ring and smallest rear the derailleur is filipped right back almost on itself .......getting frustrated now

 

[al78]

I would like help please on a good guide on how to size the chain lenth I need ?
I have checked out many online guides but still unsure as the one where you work out your largest front rings teeth eg 42 then largest cassette ring eg 32 then add chain stay length which is 43cm from crank centre to rear wheel axel centre then press calculate which gives me 137.16cm or 54 links....I tried this but when chain on largest front ring and largest rear sprocket derailleur cage is pointing forward under full stretch and strain but works perfect on other 2 front rings ?

I think 1 more link added will be ok but when its on smallest front ring and smallest rear the derailleur is filipped right back almost on itself .......getting frustrated now

The optimum length is one link more than required to wrap the chain around the largest sprocket and largest chainring (don't run the chain through the rear derailleur).

http://sheldonbrown.com/derailer-adjustment.html#chain

 

[deano69]

The optimum length is one link more than required to wrap the chain around the largest sprocket and largest chainring (don't run the chain through the rear derailleur).

http://sheldonbrown.com/derailer-adjustment.html#chain

Much appreciated,

 

[sabian92]

I found that running it over the biggest sprocket and chainring and through the deraileur when it's at a 90 degree angle to the bike (straight down) works for me. That's how I did it when I changed my chain a few months ago for the first time and I've not had a single problem.

 

[Scilly Suffolk]

Three different methods on Park Tool.

Park Tool and Sheldon Brown are two of the most generally useful sites I know.

 

[mickle]

What al78 said. Works every time.

 

[RecordAceFromNew]

I would like help please on a good guide on how to size the chain lenth I need ?
I have checked out many online guides but still unsure as the one where you work out your largest front rings teeth eg 42 then largest cassette ring eg 32 then add chain stay length which is 43cm from crank centre to rear wheel axel centre then press calculate which gives me 137.16cm or 54 links....I tried this but when chain on largest front ring and largest rear sprocket derailleur cage is pointing forward under full stretch and strain but works perfect on other 2 front rings ?

I think 1 more link added will be ok but when its on smallest front ring and smallest rear the derailleur is filipped right back almost on itself .......getting frustrated now

As they say, there is no room for debate in mathematics - the formula I figure you have used is, frankly, infallible. You can only get the chain length wrong if you get the tooth count, or link count, or stay length measurement wrong. It WILL deliver this:

The only other comment I would like to add, is if your rear mech has excess capacity,e.g. officially 43T like many Shimano SGS mechs have while you are running 42/34/24 and 32/11, then you have at least 4T spare capacity. Each 4T spare capacity will let you run a chain longer by 2 links (i.e. 1 inch or 1 pair) than calculated.