New Cassette

[Sluicehoops]

Hi,

I currently have a 12-25 casstte. If I were to change it to 11-28 would i need to increase the chain length (i plan to replace the chain at the same time)?
Is there a way of working out the required chain length or is it just trial & error?

Thanks.

 

[PpPete]

There are various on-line calculators in which you input size of cogs and chainstay length, but my favorite is simply to wrap the chain round largest chainring and largest sprocket (not through derailleur) - then add an inch (i.e. one outer and one inner link). Obviously you need to finish on inner links on both ends (assuming you are using a quick link) so it might be adding slightly more length than just an inch.

 

[RecordAceFromNew]

This is my preferred tool.

 

[Svendo]

BUT, if you never use the big ring/big sprocket combination you can probably get away without lengthening the chain. If you're confident you won't use the big ring/second biggest sprocket combination you'll definitely get away with it. Especially useful to know if using a different cassette temporarily, for a big sportive for instance.

 

[HLaB]

BUT, if you never use the big ring/big sprocket combination you can probably get away without lengthening the chain. If you're confident you won't use the big ring/second biggest sprocket combination you'll definitely get away with it. Especially useful to know if using a different cassette temporarily, for a big sportive for instance.

Yeah I'd just fitted a new chain on an old (11-25) cassette but as expected it slipped so I ordered a new cassette but I got a cheapish SRAM (11-26). I thought I'd get away with it avoiding the lowest gear a worked for a few weeks until I encountered a steep hill and forgot, split the jockey cage in half the hanger which is supposed to go first stayed true

 

[Cubist]

Wrap the chain around the biggest chainring and biggest sprocket, then add TWO full links.

 

[Sluicehoops]

Thanks for the replies.
Yes the whole point is to have a lower gear than i've got now. I'll give the various methods a go.
Thanks.

 

[Milo]

I went from a 30 t to a 32 t without changing chain length and it seems to have been OK and I did check with the bad combos. Of course that's because I am a lazy arse.

 

[chillyuk]

I have read this thread with interest as I have to fit a new chain later on today. I have always used the wrap the biggest ring/biggest sprocket plus a full link. I usually slot the joining link onto the chain and this forms part of the extra link. Being pedantic, just how critical is the chain length. One post in this thread says chainwheel/sprocket plus TWO extra links. Would you then add the joining link. In reality does a link one way or the other make a lot of difference, especially with long caged mechs. All I will be doing today is measuring the old chain and matching the new, so my questions are really just for interest.

 

[Scilly Suffolk]

I wouldn't like to say for certain, but bearing in mind a derailleur's range of movement it seems likely that a link either way is not going to junk the mech.

However, bearing in mind the possible consequences and that it is so simple to do, I take the time to get it right.

Personally I always check each time I change the chain, rather than just matching new to old, in case I made a mistake last time.

Three different methods from Park Tools here.

 

[RecordAceFromNew]

I have read this thread with interest as I have to fit a new chain later on today. I have always used the wrap the biggest ring/biggest sprocket plus a full link. I usually slot the joining link onto the chain and this forms part of the extra link. Being pedantic, just how critical is the chain length. One post in this thread says chainwheel/sprocket plus TWO extra links. Would you then add the joining link. In reality does a link one way or the other make a lot of difference, especially with long caged mechs. All I will be doing today is measuring the old chain and matching the new, so my questions are really just for interest.

Being pedantic, it is a deal breaker, because for normal chain one always has to add or subtract TWO links, since consecutive links can't/won't be identical...

For roadside mental calculation, it might be useful to remember that 4 teeth equates to two links, and best to err on the long side for obvious reason.

Whether mech is long cage or otherwise, they all have wrap limits, so adding/subtracting two links can matter. If however one knows the wrap limit is nowhere near being breached, and if one doesn't mind carrying a little extra weight, there is no reason why one couldn't keep the chain longer than necessary (determined by calculator with sprocket sizes up to wrap limit) for future flexibility e.g.

 

[Scilly Suffolk]

Being pedantic, it is a deal breaker, because for normal chain one always has to add or subtract TWO links, since consecutive links can't/won't be identical...

Good point: I stand corrected.

 

[andrew_s]

Being pedantic, just how critical is the chain length. One post in this thread says chainwheel/sprocket plus TWO extra links. Would you then add the joining link. In reality does a link one way or the other make a lot of difference, especially with long caged mechs.

There's always a little uncertainty when talking about chain links. Sometimes one link is the distance between adjacent pins (0.5"), and sometimes it's the distance between a pin and the corresponding pin on the next outer plate (1"). The normal recommendation is to take the shortest chain that you could join up round the big/big combination, then add one inch extra of chain. This would include the joining link (since the recommendation predates the existence of joining links).

The point of the exercise is to make sure that the chain is long enough that you can change into big/big without anything jamming up or breaking. You should always check this on the workstand before going out on the road.
If you've cut the chain too short you will have to add another joining link and an inner link from the offcut. There's no problem with this, other than the cost of the extra joining link.
If the chain is too long or the mech cage isn't long enough for the gears you are using, it will hang slack in the small/small. This is less of a problem - it's just a bit noisy and the chain may derail more easily.