davei1980

What's the relationship between an RD's cage length and max cog tooth capacity?

Example: I was running an Ultegra 10 sp (5600 or close to it) set up, long cage version of the RD with a 12-27 rear cassette. I think about 30 tooth max maybe with my 1x setup but couldn't shift my 11-36 cassette because it couldn't reach the largest cog.

Ordered a new shifter and now running my Shimano Zee (dyna sys family) ULTRA short cage RD with my 11-36 rear cassette and it shifts fine. Ok, I know the paperwork says 32T max but I am running a 1x setup (which I am told allows you to fudge a little more) AND I have been told Shimano is conservative with their estimates. Bottom line: the ULTRA short cage RD I have can reach a larger cog than my long cage Ultegra.

Is there a relationship between cage length and the max cog size?

I am guessing there IS, but because of some OTHER sciency-differences between the two RDs, the Zee dyna sys RD has more range despite the shorter cage, not because of it but you guys tell me?

I have pics if you need them, but you will have to just trust me that the Ultegra long cage would not work on the 36T cog but the Zee will.

Bill Kapaun

There's also chain wrap capacity which would be needed if you had multiple rings up front.

Also keep in mind that large cogs & "road" anything did not coexist back then. Now they are designing "road" RDER's to handle bigger cogs than previously.

HillRider

Cage length doesn't control the maximum cog size the derailleur will shift too, only how much chain the derailleur will "wrap up". Maximum cog is determined by the geometry of the parallelogram and location of the jockey wheel.

AnkleWork

Search "ceteris paribus."

davei1980

Brilliant! Makes sense and also why the articulation ratio is different.

So a 1x drive train may not need a very long cage even with 50t low gear if you’re running a relatively small chainring? But all such drivetrains seem to have RDs with super long cages??

Andrew R Stewart 

To repeat cage length is about chain wrap capacity. So a 11-50 cassette has a 39T wrap need. A 30-39-53 and 11-25 cassette has a 37 tooth wrap. So ring count isn't toe sole factor for wrap capacity.

Cage design has a lot of contribution to max cog capacity and shifting "quickness". With a cage pivot that is also the guide pully pivot controlling the gap between the guide pulley and the cog's undersides is up to the slant of the parallelogram and balancing cage/B pivot springs tensions. If the B pivot is also fixed then it's the slant that keeps this critical gap consistent. Tracking the slope of a 11-50 cassette is a tough ask for the der.

If the cage has it's pivot off set from the guide pulley's then as the cage rotates , about it's pivot, the guide pulley can also raise or lower WRT the cogs' undersides. This is what Shimano took to the bank for decades, along with that spring loaded B pivot and it's tension adjustment.

For a better understanding of der development and design I suggest The Dancing Chain by Frank Berto. Andy

davei1980

Brilliant! this explains a lot! Btw I love having the tension adjustment on the shifter.

Retro Grouch 

With a 1x drivetrain the size of the chainring does not affect chain wrap requirements. It's all about your cassette.

An 11/36 cassette only needs 25 teeth of chain wrap. Most any derailleur will do that. 11/50 needs 39 teeth. You'll want to check your derailleur's specs with that one.

redlude97

I dunno, all of the sram CX1 cages are pretty short and have limited capacity while being able to clear a larger max cog. For example the medium cage goes to a 36T but only allows for a 25t capacity.

davei1980

You guys are the best. Thanks for de mystifying this for me.

tomtomtom123

The specs don't say 32T max cog for the Shimano Zee. The RD comes in 2 versions, Freeride is 36T max, Downhill is 28T max. You probably have the Freeride version, which is maybe why it works fine on your 36T cog.

JohnDThompson 

Correct, provided the gear spread on the cluster is within the derailleur's wrap capacity, and the derailleur hanger can position the pulley cage low enough to clear a 50T cog.

Because the clusters have a wide spread of tooth counts that require a lot of chain wrap capacity.