Chain Length Due to Gearing Change

drewesq

I recently had a mobile mechanic change out the cassette on my cross bike from an 11-28 to an 11-30 (or 11-32 I can't remember). It has a 10 speed Tiagra.

Now, because I have 4 bikes I wanted to learn for myself how to change stuff/fix stuff and because the rear mech was a short one I changed it out myself for a longer one but I didn't change the chain.

I now want to use this bike for a bit of touring so want even lower gearing so I have a 34T small ring to replace the existing 36T which will make it 46/34T which I think will be ideal.

My question is after I remove the old chain and fit the new ring how will I know what length the new chain needs to be or will it come the correct size out of the box?

Chain: KMC X10-93 Cycle Chain 10 Speed Silver Shimano/Campagnolo

arthur_scrimshaw

I use no 3 on the link below

http://www.parktool.com/blog/repair-help/chain-length-sizing#article-section-2

drlodge

I use smallest cog and smallest chain ring method...means the chain is as long as possible.

drewesq

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19726484#p19726484]drlodge[/url] wrote:

I use smallest cog and smallest chain ring method...means the chain is as long as possible.

Apologies; wouldn't it be smallest cog/largest chainring make it the longest?

arlowood

It should be largest chainring and largest rear sprocket IIRC

However I never rely on that method now - just use the calculator in the link below

http://www.machinehead-software.co.uk/bike/chain_length/chainlengthcalc.html

k-dog

All of the methods are valid - but when you're trying to get an extreme gear I find that you need to put it on and see how it works. Start long obviously as you can't really add links back in.

Just out it in and see that the big/big combo works without being too tight and the small/small works without being so slack that the derailleur rubs in the chain. Then just adjust as necessary.

I've found that using the big/big +2 method errs on the side of a bit too long so it's a good starting point.

rolf_f

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19726868#p19726868]k-dog[/url] wrote:

All of the methods are valid - but when you're trying to get an extreme gear I find that you need to put it on and see how it works. Start long obviously as you can't really add links back in.

Just out it in and see that the big/big combo works without being too tight and the small/small works without being so slack that the derailleur rubs in the chain. Then just adjust as necessary.

I've found that using the big/big +2 method errs on the side of a bit too long so it's a good starting point.

+1. Works for me. Basically do one (eg big big) and see how then that works in small small. If small small isn't working, go back to big big and pull out a bit of the slack to see if the rear mech can handle a couple more links out.