Difference between Long and short Cage for Rear Derailleur

[GoLefty!!]

Yo Johan, I still owe you a Yellow Saddles coffee.

 

Hairy, yip, the 1 and only

[Hairy]

His advice might be OK but his opinions need work.

 

You could tag a vast majority of posters with that comment.

 

In this particular thread TNT's "take it or leave it" comment would be a prime example.

[awesme]

Hi guys

 

Ok I accept that what I'm trying to do will work, got enough brainy people having told me, thanks brainy people...

 

now, from what I can see my min and max teeth counts also match the Shimano site, as per my earlier post.

 

JB: where does your math fit in, can't find the numbers, teeth range/capability number you mentioned on the Shimano site?

 

Big wheel - smallest wheel = dif

Big Cassette gear - smallest gear = dif

Add the two difs together, this number, where on the Shimano doc's do I get it, just so that I learn out of this, know where to look.

 

My rations will be

 

42/32/24 = 18

34/11 = 23

Magic number = 41

 

G

[Johan Bornman]

Hi guys

 

Ok I accept that what I'm trying to do will work, got enough brainy people having told me, thanks brainy people...

 

now, from what I can see my min and max teeth counts also match the Shimano site, as per my earlier post.

 

JB: where does your math fit in, can't find the numbers, teeth range/capability number you mentioned on the Shimano site?

 

Big wheel - smallest wheel = dif

Big Cassette gear - smallest gear = dif

Add the two difs together, this number, where on the Shimano doc's do I get it, just so that I learn out of this, know where to look.

 

My rations will be

 

42/32/24 = 18

34/11 = 23

Magic number = 41

 

G

Splat gave you some real life examples on Page 1 of this Fred.

 

You can get the derailer consumer instructions from techdocs.shimano.com.

 

I have a brochure in my hand for the RD-M972.

 

According to that, the capacity for the RD-M972/RD-M772 is 45T (where T=teef) for the long cage and 33T for the medium cage

 

etc etc. As long as your combo is equal to or smaller than the number the derailer will work. Like Lefty says, it may be excessive in some cases, but it will work.

[GoLefty!!]

The you require an SGS or LOng Cage rear deraileur.

For optimum performance on a GS (Medium Cage your range should be 35T

 

so mine drivetrain

 

44/29 = 15

11/32 = 21

=36T

A GS will be just at its absolute limit. and that holds true in practice. But bare in mind that at that extremes you will do other damage to the drivetrain.

You can mamange the effective range yourself by preventing yourself from using extreme gears.

 

PS: Above examl is for M980 XTR.

Always checks the technical data sheet for a derailleur to find its gear capacity.

Edited October 18, 2012 by GoLefty!!

[GoLefty!!]

The derailleurs you are looking at ate pretty much stock standard with some flexibility in mounting arrangement for the front derailleur.

 

maybe you posted earlier but what frame is this all going to fit on?

 

I ask because will the frame, BB and Cahinset allow for a 50mm chainline or a 48mm chainline.

 

Its important to check because if you fit a FDdesigned for 48mm chainline, you may get annoying chain rub in the lower gears which you won;tbe able to dial out without bending the derailleur cage plate.

Vice a versa, if you use a 48mm chainline FD on a 50mm chainline bike you may never get the chain onto the big ring.

[awesme]

Thanks JB/GoLefty:

 

Just trying to get that doc, and find that reference/number on it.

 

Found the number in the docs. so I have a 45 T capability, and need 41, so I'm just prob in a sweet spot for the long cage then.

 

G

 

 

Splat gave you some real life examples on Page 1 of this Fred.

 

You can get the derailer consumer instructions from techdocs.shimano.com.

 

I have a brochure in my hand for the RD-M972.

 

According to that, the capacity for the RD-M972/RD-M772 is 45T (where T=teef) for the long cage and 33T for the medium cage

 

etc etc. As long as your combo is equal to or smaller than the number the derailer will work. Like Lefty says, it may be excessive in some cases, but it will work.

[awesme]

GoLefty, nope I haven't mentioned that little fact.

 

will PM you, small little project for next couple of months...

 

G

 

The derailleurs you are looking at ate pretty much stock standard with some flexibility in mounting arrangement for the front derailleur.

 

maybe you posted earlier but what frame is this all going to fit on?

 

I ask because will the frame, BB and Cahinset allow for a 50mm chainline or a 48mm chainline.

 

Its important to check because if you fit a FDdesigned for 48mm chainline, you may get annoying chain rub in the lower gears which you won;tbe able to dial out without bending the derailleur cage plate.

Vice a versa, if you use a 48mm chainline FD on a 50mm chainline bike you may never get the chain onto the big ring.

[olram_df]

@splat how does the formula work for a 1x9?

[Johan Bornman]

@splat how does the formula work for a 1x9?

The derailer doesn't care whether you have ten chainrings and 20 sprockets. All it cares about is the total difference.

 

I your case, add zero to the difference between your largest and smallest sprockets.

[kosmonooit]

Don't know if its been mentioned, but the net effect of using too short a cage will be difficulty / sticky gears when it comes to shifting down on te RD when on the big ring up front. At least, that is what I have found to tbe the diffs with medium cage and 11-32 on the rear (9-speed)

[GoLefty!!]

The derailer doesn't care whether you have ten chainrings and 20 sprockets. All it cares about is the total difference.

 

I your case, add zero to the difference between your largest and smallest sprockets.

 

 

+1

chain length governs the functioning here.

[GoLefty!!]

Don't know if its been mentioned, but the net effect of using too short a cage will be difficulty / sticky gears when it comes to shifting down on te RD when on the big ring up front. At least, that is what I have found to tbe the diffs with medium cage and 11-32 on the rear (9-speed)

 

You have another problem going on there. Did you shorten the chain too much when you had the mdeium cage by anychance?

[kosmonooit]

You have another problem going on there. Did you shorten the chain too much when you had the mdeium cage by anychance?

 

Nope but what I figure is that the less reach of the RD means more tension on the chain when its on the bigger rings. This became a problem due to neglect of regular cleaning (its my pavement warrior commuter) and after a good clean and lube, it was okay again. Maybe I should say its a hypothesis.

[GoLefty!!]

sounds more like binding within the chain itself. the tension is not significantly greater across the range of movement of the lower cage. Its pretensioned during assembly at the factory to ensure that the spring force is fairly constant across the range of motion. This is one of the many design features of modern derailleurs that makes them so much more precise and quieter than those from 20yrs ago.