Cassette gearing change/chain length question

[bluekudu]

We're riding the Iron Horse in Durango this Saturday and I am thinking about swapping the 12-25 cassette on my wife's bike for an 11-28. Will I need to add a link or should the chain be close enough to work?

Thanks

[Ken Robb]

I think she would only have a problem if she cross-chained onto the big/big combo and that's not likely is it?

[bluekudu]

Thanks Ken. Likely yes, but not on most of the road to Silverton. Sounds like the ideal is to add link/s as needed.

[zmudshark]

I would think it would depend on how it was sized to begin with. Is it Campy or something else?

I size Campy so that I have tension on the RD in small/small. Everything else seems to fall in place from there.

YMMV, there has been lots of 'discussion' on this.

[bluekudu]

It's 07/08 ultegra (6600? Silver group, not SL gray) with a recently installed (<100 miles) 6701 chain. I am sitting here visualizing the difference in diameter a couple/few extra teeth can make and it seems a link or two would be necessary in a big/big chain measurement. She does a few+ rides here in our backyard up to 8500 feet-ish so probably the right thing is to put on a new chain with the new cassette and never look back at the 12-25. Not sure what bad could happen if she cross chained on flats but if it involves more than rapid wear and includes a potential hit to the pavement, I'd rather not take that chance. Thanks for helping me think this through.

[Ralph]

It's easy to figure out. Put it in big to big and see if it's got enough chain left for a slightly larger cassette cog. On my bikes, it wouldn't be a problem to add a slightly larger cog.

[Tony T]

If you already have the cassette, just install and see if the current length is ok

[cmbicycles]

Is your derailleur a short or o long cage? Long cage might do fine, short may not depending on the rest of your setup. Just try it out early enough to add a link if needed. You may run into issues with the small/small, again depending on the rest of your setup.

[dave thompson]

Is your derailleur a short or o long cage? Long cage might do fine, short may not depending on the rest of your setup. Just try it out early enough to add a link if needed. You may run into issues with the small/small, again depending on the rest of your setup.

The derailleur being a long or short cage has no bearing on the size of the cassette being used, a long cage (road) has the extra wrap capacity to to take up the chain slack if a triple crank is use. A short cage derailleur can be use with a 32t cassette in some cases. Most any Shimano rear derailleur can handle a 28t cassette, even though they're 'rated' for 27t.

I would add a complete link of chain just to ensure the same gear combos can be used safely as before the cassette swap.

[Tony T]

I would add a complete link of chain just to ensure the same gear combos can be used safely as before the cassette swap.

Wouldn't it be easier to install the cassette to see if the chain is long enough?

.

[Chance]

The derailleur being a long or short cage has no bearing on the size of the cassette being used, a long cage (road) has the extra wrap capacity to to take up the chain slack if a triple crank is use. A short cage derailleur can be use with a 32t cassette in some cases. Most any Shimano rear derailleur can handle a 28t cassette, even though they're 'rated' for 27t.


cmbicycle is probably saying that if the derailleur was a long cage (from a triple) it would likely have enough extra (chain slack) capacity so that it could handle the extra 3 teeth on the large side without having to add extra chain.

[Chance]

We're riding the Iron Horse in Durango this Saturday and I am thinking about swapping the 12-25 cassette on my wife's bike for an 11-28. Will I need to add a link or should the chain be close enough to work?

Thanks

It's 07/08 ultegra (6600? Silver group, not SL gray) with a recently installed (<100 miles) 6701 chain. I am sitting here visualizing the difference in diameter a couple/few extra teeth can make and it seems a link or two would be necessary in a big/big chain measurement. She does a few+ rides here in our backyard up to 8500 feet-ish so probably the right thing is to put on a new chain with the new cassette and never look back at the 12-25. Not sure what bad could happen if she cross chained on flats but if it involves more than rapid wear and includes a potential hit to the pavement, I'd rather not take that chance. Thanks for helping me think this through.

If your chain was cut using the small-small technique of measurement (my personal preference), then changing from a 12-25 to an 11-28 may not require additional chain at all. In fact, adding additional chain may be a bad idea because it would limit the small-small combinations. Depending on what rings you are using (compact versus 53-39 or others) you may be just fine if chain was cut with small-small measurement. As long as RD has enough capacity to handle the entire range you are not changing much provided you are only going from a 12T to 11T small cog. Best to try it first before adding more chain as others have suggested.