Cassette change, new chain length?

pete54

My chain is worn and I want to change my cassette from a 12-23 to a 12-25 at the same time. I'm not too confident in sizing chains, so would I be correct in assuming that making the new chain one (or two) links longer than the old one would be ok?

Thanks,

Pete

alfablue

Just set the chain to the correct length (it is unwise to assume it was correct in the first place). Do this by threading through front and rear mechs (i.e. installed as normal) and set the length so that whilst on big chain ring and small rear sprocket, the jockey wheels on the rear mech are vertically aligned. (This is the method recommended by Shimano, there are other approaches but this works fine on road bikes).

domhopson

Have a look at this "how to"

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

That should have all the info you need

pete54

Thanks, I guess it's best to do the job properly. I'll have a look at the Park website. It's not a road bike (Specialized Sirrus), but has a Sora rear mech and a Sugino triple chainset, so I guess that the same principles apply.

Pete

sungod

as alfablue says, for sora the shimano instructions are that with the chain on largest chain ring and smallest sprocket, the chain length should be adjusted so that the axles of the jockey wheels are verticaly in line

see http://techdocs.shimano.com for full details