Bicycle Mechanics - 12-27 with 53-39 Short Cage?

Jut got a really nice new ride, Fuji Team RC (53-39 with 12-23). Old ride is a Fuji Team 53-39-30 with 12-27.
I am gonna have a real hard time climbing the hills around here on the new ride, so I want to go to a 12-27 on the rear, or at least a 12-25. This is DuraAce stuff, short cage der, and the chain ONLY has 106 links and looks close to the limit when I do big/big. I do not think I could ever get a 12-27 to work with this chain and der. But the question is if I lengthen the chain so a 27 works is it gonna be too sloppy on the other extreme? I have other wheels, one with a 12-25, and 12-27 on the triple so I can experiment, but do not want to ruin a brand new chain unless I have to. I can't even use this chain on the triple since its length is 108 links.

So I guess the question is, do folks run 12-27 on short cage DuraAce doubles with a 53 big ring?

Thanks for any assistance in advance!

I'm running a 50-34 crankset and a 12/27 with a short cage. Works fine, but I do avoid the big-big, small-small combos.

Have Dura Ace and 105 short cage derailleurs running 30t off 53/38 cranks, or 32t off 53/42 cranks ok (supposedly even 34t work for some with 42t front, but at some point the RD won't take up enough slack). Usually need to wrap a new chain around the big-big combo. DA is spec'd to do 27t, but will do more.

Edit: take out a small cog and try several sizes of loose mountain cogs (with shift ramps plus a spacer), taken from a cheap cassette. I run a 30t in the spring, and have a 28t bailout in the summer for our local hills.

The derailleur has a max. chain wrap capacity (listed by Shimano) of 29t. Your max. chain wrap requirement, even if you were to shift to the small ring/smallest cog combo with the 53/39 chainrings and 12 x 27 cassette, is 29t. So it should work in all combo's with the setup you describe, according to Shimano's own specs-

Chain wrap as defined on the Cycle World website:

An important part of a rear derailleur's job is keeping the chain taut as you change gears. Chain-wrap capacity is a number that tells whether or not a derailleur will be able to do this on the drivetrain you plan to use it on. Calculate chain-wrap capacity with this formula: Chain-wrap capacity = (large chainring - small chainring) + (large rear cog - small rear cog). Example: 44/29 chainrings and a 11-28 cassette: (44 - 29 = 15) + (28 - 11 = 17) = 32-tooth chain-wrap capacity.

I'm running that exact combo on my Roubaix, using 105 ders F&R, with absolutely no problems. Just avoid big-big and small-small, which is pretty much a no-no anyway. The Roubaix came originally with 50-34, and all I did was change the crankset.

Chain wrap as defined on the Cycle World website:

An important part of a rear derailleur's job is keeping the chain taut as you change gears. Chain-wrap capacity is a number that tells whether or not a derailleur will be able to do this on the drivetrain you plan to use it on. Calculate chain-wrap capacity with this formula: Chain-wrap capacity = (large chainring - small chainring) + (large rear cog - small rear cog). Example: 44/29 chainrings and a 11-28 cassette: (44 - 29 = 15) + (28 - 11 = 17) = 32-tooth chain-wrap capacity.


I don't think that's the best wording. The chainrings and cogs combo doesn't have chain wrap capacity, it has a maximum chain wrap requirement. It's the derailleur that has chain wrap capacity. As I mentioned earlier, the proposed setup by the OP falls within Shimano's published specs for this derailleur. (53-39) + (27-12)=29. The Dura Ace short cage RD has a max. chain wrap capacity of 29t. Just make sure to size the chain properly-

^ Well yes they should have used requirement for the gears, but it does a good job of explaining how to find out what capacity you need (the requirement).

When I was trying to find out if I needed a long cage with my 50/34 and 13-29 setup, someone telling me my short cage has a chainwrap capacity of 28 didn't help me at all until I looked up what chainwrap was.

So I guess the question is, do folks run 12-27 on short cage DuraAce doubles with a 53 big ring?

Yes.

Doesn't necessarily mean that your chain is the right length, though.

Thanks guys,

I KNOW the chain, as it is, is too short, so when I do it, a new chain is required with the new cassette.

This forum is just wonderful!!!!

You can extend a chain. Don't have to buy a new one. Get some leftover pieces at your LBS.

You can extend a chain. Don't have to buy a new one. Get some leftover pieces at your LBS.

Ya know, I actually have 6 new links from a previous chain change. I am reluctant to do this with the 10 speed Shimano pin deal, but I guess it would be OK? Or would I be better getting a link that I could add that you can rebreak like a Connex? What works on Shimano 10 Speeds?

The right size Connex works (there are at least three), and Superlink has a new one that they say will work.

If you add links, though, you're still going to have to use at least one pin. Why the reluctance?

The right size Connex works (there are at least three), and Superlink has a new one that they say will work.

If you add links, though, you're still going to have to use at least one pin. Why the reluctance?

Guess it is that those pins are supposed to be the weak links, and I would now have not 1 but 3 pins in the chain, two of them very close to each other. But it probably makes no difference, so I think I will try that and save the price of a new chain. And as I said, I have a 12-27 on my other Fuji to play with.

I will do nothing for a while with this brand new bike, I want to see how bad the stock stuff is for my old fat body!!!

Shimano replacement pins shouldn't be a weak area. As far as I can tell people don't like them because they aren't reusable.

Btw, be sure you don't press out and refit a replacement pin, even with a new one. (With the replacement pins it's hard to tell them from the original rivets looking from the drive side, so check the back side (where the nose snaps off) if you're unsure.) Once the replacement pin has been set it expands the hole so next pin won't stay. Replace the whole link if you have to.

Just completed the task of replacing the 12-23 with a 12-27 cassette. Had to add 1 link to the chain, and take the "B" screw way in, 3 full turns!! Now it works even with big/big in case I screw up and crosschain which I always do without thinking!!

DMF, I did just use 2 pins.

It's unlikely that you will need to add any chain but you should check to make sure the derailleur does not reach its forward limit of travel in the big to big combination, just in case you accidentally shift there.
The short cage derailleur will absolutely handle 53/39, 12-27. I've run various wheels with 12-23, 13-25, 13-26, and 12-27 cassettes on my D-A with short cage RD, no adjustments needed.

Al

I absolutely HAD to add 1 link on my Team RC. I had tried another wheel with a 12-27, and almost broke the der is was so tight. It was only 106 links, my other Fuji Team came with 108 links which is what the RC now is.

No problem. I set up a friend's ultegra with that combo and it only required a longer chain. He needed a new chain anyway.