Setting chain length with a mid-length rear derailleur cage

[legrandefromage]

not if your single chainring is 42 or 44 or just bleedin huge

 

[d8mok]

Re:

I think you missed my point .....


Anyway sizing a chain on a 1x system is as simple as it gets and is totally different to a retro set up.

 

[legrandefromage]

you still need to shift big big because there is no choice but the mechs have that extra reach to go to 52t rear

on a 2x or 3x chainset, good chainline gives you the choice of just about any gear you could wish for

 

[Fatal Swan]

I think the same as jimo746, you probably have it as good as you can already. Big-big and small-small shouldn't happen in practice but you don't you don't want to risk tearing your mech/hanger off the frame and into your spokes if it does... Big-big is a risk in that respect and small-small isn't, so set the chain length so that big-big is usable "just in case", albeit stretched as much as you're comfortable with. Then any rubbing on the cage/chain slackness in small-small due to the chain being too long will just be a reminder that you should be in a different chainring anyway. If that's still too much of an irritation then the options are a cassette with a closer ratio or a longer cage mech.

 

[hookooekoo]

Re: Re:

Why would you use the granny ring with smallest cogs and why on earth would you be anywhere near using the big/big ?

Cross chaining and the fact that ratios will be doubled up by using better combos

I think you are trying to solve a problem that doesn’t (shouldn’t) exist

You are absolutely right when you say that those combinations should be avoided. Although my experience of shifting from granny ring to middle ring on early 1990s Shimano chainrings is that you should try to avoid it when on a technical section of trail, because there might be quite a bit of grinding and scraping before the chain hooks onto the middle ring. That means there might be short periods of time when I want to use combinations that sub optimal. Later Shimano chainrings were, in my opinion, much better, as they had little hooks at several places, rather than just a few half height teeth as found on early 1990s chainrings.

By the way, may I ask your opinion of the modern 1 x 10, 1 x 11, and 1 x 12 setups? I'm guessing you think it's a regression in design due to the extreme chain lines.

 

[trailwright]

Re:

I have the same rear mech and have always set up my chains using the small- small method. Thus the right length allows the chain to run unimpeded but 1 extra link would result in rubbing on the underside of the rear mech. On a 46-36-26 x 12-32 set up this equates to 112 chain links.

I can technically get into the 46x32 but this is not a gear that should be getting used anyway, with a better combo served by the 36 and somewhere lower down the cassette.

 

[hookooekoo]

^ Agree.

While you are over the rated capacity limit for a GS due to the triple, in practice with sensible shifting practices it's a non-issue.

(46 - 24) + (28 - 12) = 38T

If you do not do big-big: (46 - 24) + (24 - 12) = 34T

If you do not do small-small: (46 - 24) + (28 - 13) = 37T

You are best not bothering with silly half-links. Set the chain length for small-small where the cage tension just starts
without the upper jockey wheel hitting the lower chain run and you will be fine. The mech will cope with the rest
with only a potential issue of chain-slap on the small-small combos if you are riding over bumpy ground at speed.

I routinely push Shimano mechs over the rated limits, not only capacity but also max sprocket size.

Thanks for reminding me how the calculation should be done.

I remember back in the 1990s, it wasn't that uncommon to see people on MTBs using a short cage road mech with a close ratio road cassette!

 

[hamster]

My setup is 28-12 and 46-36-24. I'm guessing that's slightly too much for the 'Total 33T' maximum difference that's stamped on the dérailleur cage, although I can't remember how to calculate the maximum difference on my setup.

I'm puzzled about this - did Shimano change cage lengths over the years?
I run an M750 XT short cage (well it's mid cage really compared to road) with 13-30 and 47/38/24 on my tourer no bother.
With a short cage version of M735 it's getting close to running out with 11-28 and 34/46.

Off to the shed to measure...

 

[d8mok]

Re: Re:

Why would you use the granny ring with smallest cogs and why on earth would you be anywhere near using the big/big ?

Cross chaining and the fact that ratios will be doubled up by using better combos

I think you are trying to solve a problem that doesn’t (shouldn’t) exist

You are absolutely right when you say that those combinations should be avoided. Although my experience of shifting from granny ring to middle ring on early 1990s Shimano chainrings is that you should try to avoid it when on a technical section of trail, because there might be quite a bit of grinding and scraping before the chain hooks onto the middle ring. That means there might be short periods of time when I want to use combinations that sub optimal. Later Shimano chainrings were, in my opinion, much better, as they had little hooks at several places, rather than just a few half height teeth as found on early 1990s chainrings.

By the way, may I ask your opinion of the modern 1 x 10, 1 x 11, and 1 x 12 setups? I'm guessing you think it's a regression in design due to the extreme chain lines.

I think the 1x systems are great. Chain lines aren’t bad at all as the front chainring is designed to be central mostly for the system. Wouldn’t use anything else on a bike I intend to ride properly

 

[hookooekoo]

My setup is 28-12 and 46-36-24. I'm guessing that's slightly too much for the 'Total 33T' maximum difference that's stamped on the dérailleur cage, although I can't remember how to calculate the maximum difference on my setup.

I'm puzzled about this - did Shimano change cage lengths over the years?
I run an M750 XT short cage (well it's mid cage really compared to road) with 13-30 and 47/38/24 on my tourer no bother.
With a short cage version of M735 it's getting close to running out with 11-28 and 34/46.

Off to the shed to measure...

My RD-M900 is 67mm measured from centre to centre of pulley bolts.
Same measurement for RD-MT62 is 86mm.