Cassette 11-32 to 12-30. Do I need to re-size the chain?

smthompson

I'm currently running Sram Rival with a 11-32 cassette on my commuting bike but have found the gaps in the ratios a bit wide. I have ordered a Miche 12-30 cassette. Will I need to remove any chain links when I fit it?

timothyw

Nope, it'll be fine.

smthompson

Thanks for the help....

The Rookie

The difference in wrap is only 1 link (not 1 pair) so while you 'may' be able to remove one pair, its not really worth it.

drlodge

The new cassette is less extreme than the old one (smallest cog is bigger, biggest cog is smaller), so no, it'll be fine.

smthompson

Thanks All

The Rookie

Eh? Smallest cog has no effect on chain length whatsoever!

drlodge

The Rookie wrote:

Eh? Smallest cog has no effect on chain length whatsoever!

Yes it does. If the smallest cog gets smaller, then the rear derailleur may no longer take up all the slack i.e. if the chain was originally set to its longest possible length. Probably not going to be an issue e.g. changing from a 12T to 11T, but could potentially happen.

The Rookie

Read how Shimano (et al) tell you to size a chain and then try and explain how the size of the small ring effects chain length, as the answer is not at all.

drlodge

The Rookie wrote:

Read how Shimano (et al) tell you to size a chain and then try and explain how the size of the small ring effects chain length, as the answer is not at all.

Ok for your benefit I will.

Say the capacity of the rear derailleur is 34T and you have a 12-30 cassette and compact 50/34. That means the RD is at the limit of its capacity (the numbers are irrelevant, important point for this example is that the RD capacity is at the limit).
If you now fit a cassette with a 11T or smaller sprocket and keep the chain length the same, the RD will now be exceeding its capacity and when on small chainring-small sprocket the chain may well be slack. Same would apply if you fitted a cassette with a 31T or bigger sprocket - when in big-big the RD would likely get ripped off.

The Rookie

So you still haven't read and learnt how you size a chain, go start with lesson 1 and find out, all the rest is then totally irrelevant.

Here you go
http://si.shimano.com/php/download.php? ... 05-ENG.pdf

drlodge

I know perfectly well how to size a chain. What you seem to be ignoring is that rear derailleurs have a finite capacity to take up chain slack, and if you lower the size of the smallest sprocket without resizing the chain, that capacity may be exceeded.

The Rookie

Well go back to the start of the thread, the question and your comment in responce, and if you knew how to size a chain why quibble over capacity and such other irrelevances, after all if the capacity was fine with an 11-32 it was hardly going to be an issue with a 12-30, is wasn't ignoring it, it was an irrelevance in the context of the question, much like the size of the smallest sprocket really.

drlodge

My response was accurate and appropriate:

The new cassette is less extreme than the old one (smallest cog is bigger, biggest cog is smaller), so no, it'll be fine.

If the new cassette had a smaller smallest sprocket I wouldn't have said what I said and it might have been an issues, But it isn't so it isn't. :roll:

The Rookie

Nope, still wrong, you just can't or won't see it, shame as that is the best way to learn (from one's mistakes) as the smallest cog is still totally and utterly irrelevant.

Initialised

For that small a difference I wouldn't bother, just remeasure next time you replace the chain.

markhewitt1978

Depends how many miles you have on your chain? Is it's good practice to replace the chain if you're replacing your cassette.

rolf_f

The Rookie wrote:

Nope, still wrong, you just can't or won't see it, shame as that is the best way to learn (from one's mistakes) as the smallest cog is still totally and utterly irrelevant.

If your cage is at it's limits at both ends (ie near stretched on 'big-big' and the chain near running back over the sprockets on 'small - small') then putting a smaller smallest sprocket will result in the chain being too long. Mostly, it shouldn't be an issue but it isn't fair to say it can't be. If the smallest cog really wasn't relevant, we wouldn't need to ever shorten a chain!

Shimanos instructions already assume that the rear mech has been chosen in accordance with the gear range recommended. So normally small-small works by default - but that assumes that you aren't that close to the limits of the mech capacity as manufacturers recommendations there are extremely conservative to start with. If you are pushing the range of the mech, small small matters and is far from irrelevant.

drlodge

Thanks Rolf, that is what I was trying to explain.

The Rookie

He explains well why it isn't correct (if you read it properly), if you set it small small you assume the mech is the right size, if it's not it jams solid, I'd rather it went too slack in small small than jammed solid in big big!

gbsahne001

The Rookie wrote:

He explains well why it isn't correct (if you read it properly), if you set it small small you assume the mech is the right size, if it's not it jams solid, I'd rather it went too slack in small small than jammed solid in big big!

So would I, as I'd never use a small-small combination but I do occasionally use a big-big combination