12-27 more noisy than 12-25

Triathlon Forum
1

I have a P2C that came with a 12-25 ultegra. Had it for only one summer and did not do mad distances on it. Probably only somewhere between 1000-2000km

I had it switched to a 12-27 ultegra and it seems to me that it’s a lot noisier in all gears. Maybe it’s just an impression because I was without the bike for over a week while on vacation. Maybe it just needs a small adjustment to the derailleur. Maybe it’s normal for a 12-27. I don’t know.

2

Not normal. Swapping a 12-25 to a 12-27 will require some minor rear derailleur adjustment.

Could be from a stretched chain on a new cassette as well.

3

Could also be from a too-short chain.

4

My naive impression is that there maybe one of a few problems here.

  1. The problem could be that your derailleur is now too close to the cassette. This could lead to some contact between the two parts and producing some noise. in this case you just need to adjust the B-tension of your derailleur. It’s listed as step 4 in the service instruction manual (link below).
    http://techdocs.shimano.com/media/techdocs/content/cycle/SI/Ultegra/RD6500/SI-53Z0C_En_v1_m56577569830611842.pdf

But there should only be a problem here on the largest (27) ring getting too close to the derailleur (because that is the only gear that has changed). So this might not be the solution.

  1. Alternatively… has it been a while since you’ve changed your chain? Do you have a tool to measure chain stretch? I ask because putting on a new cassette with a worn chain could easily lead to noise and shifting problems. You would not have noticed this with your old cassette because both chain and cassette would have been worn to the same degree.
5

Assuming it’s Shimano 10sp on a non-Shimano 10 speed specific wheelset…did you include the little spacer ring on the freehub in back of the cassette? Chain length also a possibility. Also try cranking the B-screw a turn & see what happens.

6

My very first thought was the chain wear too.

Next I thought of the B screw adjustment but that would only adjust issues with the 27 as you said.

jaretj

7

I think MarcK is on the money here. If the builder cuts a chain for good performance on a 12-21 or 12-23, it’ll likely be fine on a 12-25. But maybe not on a 12-27. Does the noise happen on all cogs, or just the bigger ones?

It’s possible that the “B” screw needs a small adjustment to pivot the derailleur a little more toward the back of the bike. If the noise is big sprocket only, that could be it.