Swapping standard to compact cranks and chain length

[bcroslin]

I swapped out my Shimano standard 53/39 chain rings for 50/34 rings today and I noticed that when I'm in my small front ring and my 11 and 12 cassette cogs my chain goes slack enough to slap the chain stay. I don't ever remember this being an issue with my SRAM groups in the past. The chain is new as well as the rest of the drive train. I'm using an Ultegra short cage derailleur. The chain is obviously too long but shouldn't the same length chain be able to accommodate a standard or compact chain ring?

Bob

[RacerJRP]

As you have found out, the answer is no. You will need to take a couple links out before this causes issues such as a dropped chain/ mangled BB shell.

[kramnnim]

It can depend on what method was used to determine the chain length the first time. Your newly shortened chain might still work with your standard rings if you have a close ratio cassette...

[Louis]

I'll ask the obvious question: Why are you cross-chained 34-11 or 12? I'd avoid that if I could. (after shortening the chain to the correct length using your favorite method - since there a tons of ways to figure out THE best length)

As for the cause of the problem, the new r-der may not have as much range as the old one. A change from 39 to 34 is a significant reduction, so clearly the chain length that worked for 39-11 will be longer than for the compact.

[rustychisel]

drop front derailleur 3 ~ 4 mm

take 2 links out of chain

avoid 34 x smallest cog, and possibly 2 x smallest cogs [whereby the smaller inner chainring might cause an issue with shorter chainstay length, if it's under about 40.5 cm there are possible crosschaining issues. Over 41cm and with careful adjustment you're probably okay]

[bcroslin]

I'm using the same 11-25 cassette so the only thing different is the chain rings. I'm looking at the bike in work stand and scratching my head and not worried about cross chaining on the road. I'll knock the links out and buy another chain for the 53/39.

[oldpotatoe]

I'm using the same 11-25 cassette so the only thing different is the chain rings. I'm looking at the bike in work stand and scratching my head and not worried about cross chaining on the road. I'll knock the links out and buy another chain for the 53/39.

IF the chain was of a proper length to begin with, 1 link out, not 2, IME.

A outer plate section+ an inner plate section=1 link, BTW.

[tv_vt]

What RustyChisel said.

And don't think you can take one link out of a chain. Has to be even-numbered. Otherwise links don't line up - you need to match up an inner to an outer! (OP, to me, one link is what's between two chain pins... Guess we're saying the same thing, though.)

[oldpotatoe]

What RustyChisel said.

And don't think you can take one link out of a chain. Has to be even-numbered. Otherwise links don't line up - you need to match up an inner to an outer! (OP, to me, one link is what's between two chain pins... Guess we're saying the same thing, though.)

One link of chain

[bcroslin]

One link of chain

yep. done and done. thanks.

[tv_vt]

One link of chain

Just for my edification then, OP, when I buy a chain that has 116 links to it, are there 232 pins in it? Guessing from your diagram there would be.

[oldpotatoe]

Just for my edification then, OP, when I buy a chain that has 116 links to it, are there 232 pins in it? Guessing from your diagram there would be.

ahhh, no, each 'link' is held together by one pin, between the inner and outer plates...then one pin connecting to the next so 3 links, in a circle, have 7 pins...

my head hurts, gonna go lie down.