Rear Derailleur advice

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John D
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Rear Derailleur advice

Post by John D » 27 Apr 2016 13:43

So in anticipation of my insurers "paying out" and fed up of still using my winter bike, I have sourced a replacement for my stolen Planet X SL carbon

It has an Ulegra 6700 10 sp groupset from what I can make out with 50/34, 12/25 and a short cage rear derailleur. With the best will in the world, there are times when I will need my 28t gearing I had on my old bike and therefore propose replacing the rear cassette with a 11-28.
Having "googled" ad infinitum, there seems to be conflicting advice (certainly from Shimanos own technical info) that I will also need to replace the rear derailleur to a longer cage version. other opinions seem to say it is doable.
I am minded to just go ahead and see what happens but am hesitant in case this puts too much strain on any of the components and I risk some sort of catastrophic failure or would it just result in poor changing?

Any advice/comments gratefully received

JD

laurence_cooley
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Post by laurence_cooley » 27 Apr 2016 13:52

According to the spec sheet, the capacity of the short-cage mech is 33t. If you're running 11-28 that's a difference of 17, plus 16 for the front difference between 50 and 34, which makes 33, so you'll be fine.

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ballintrane
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Post by ballintrane » 27 Apr 2016 14:06

John i have the same groupset and use 11-28 cassette and have even ran 12-30(kiddie killer)no problem, hope this helps.

John D
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Post by John D » 27 Apr 2016 15:35

Paul, Laurence

Just the comfort I needed

Many thanks

John

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petemarshall
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Post by petemarshall » 27 Apr 2016 15:37

The crucial thing is to ensure that the top jockey wheel doesn't end up so close to the largest cog that it is trapping the chain. The b screw on Shimano derailleurs can only be screwed in enough to usually avoid the largest cog they guarantee. On road derailleurs this was 27 on 9 speeds, 28 on 10 and now 32 with 11. However this varied greatly in reality dependent on the design of the hanger.

The work around is to either replace the b screw with a longer one (it's M4 thread ) or just reverse the screw itself which pushes the jockey further away from the cog. Shifting won't be quite as smooth but it works fine.

As far as long cages go, this is about the total difference between the length of the chain when on big to big and small to small. Usually a long cage is only really required when using a triple. But when using a 11-32 on the back, if you want to use the full gear range a medium cage Ultegra will let you. Not a good idea though to actually use big to big or small to small. This is one of the main reasons people manage to break chains !

Using these traditional bodges has allowed some of us to continue to get up hills as the legs get old. I have used a 11-32 XT 9 speed cassette with a short cage Dura Ace rear and usually run a 11-30 on a 10 speed with an Ultegra mech using longer b screws in both cases. Even bodged the Dura Ace rear mech is still as smooth as a politicians lies.

John D
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Post by John D » 27 Apr 2016 17:06

petemarshall wrote:The crucial thing is to ensure that the top jockey wheel doesn't end up so close to the largest cog that it is trapping the chain. The b screw on Shimano derailleurs can only be screwed in enough to usually avoid the largest cog they guarantee. On road derailleurs this was 27 on 9 speeds, 28 on 10 and now 32 with 11. However this varied greatly in reality dependent on the design of the hanger.

The work around is to either replace the b screw with a longer one (it's M4 thread ) or just reverse the screw itself which pushes the jockey further away from the cog. Shifting won't be quite as smooth but it works fine.

As far as long cages go, this is about the total difference between the length of the chain when on big to big and small to small. Usually a long cage is only really required when using a triple. But when using a 11-32 on the back, if you want to use the full gear range a medium cage Ultegra will let you. Not a good idea though to actually use big to big or small to small. This is one of the main reasons people manage to break chains !

Using these traditional bodges has allowed some of us to continue to get up hills as the legs get old. I have used a 11-32 XT 9 speed cassette with a short cage Dura Ace rear and usually run a 11-30 on a 10 speed with an Ultegra mech using longer b screws in both cases. Even bodged the Dura Ace rear mech is still as smooth as a politicians lies.

Pete

Thanks, there have been times I'd have happily sold my children for a 30t or even a 32t, and I wouldn't rule it out in the future, however for most of my riding, a 28t will suffice.

I assume no alteration to chain length required?
Also, there doesn't seem to be an obvious "quick link" for removal for a good clean. Is there anything I should be looking for in particular or can I remove any link to replace with a reusable KMC quick link?

Cheers

John

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petemarshall
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Post by petemarshall » 27 Apr 2016 17:56

Chain length should be set at big ring to big ring plus a link, without going through the derailleur. Any change in the sizes of rings will require you to change chain length. To short and it won't shift smoothly to long and you will drop the chain when changing down at the front.
If your cadence ever drops below 70 on a hill, you need a bigger gear or a bigger heart and lungs. I find the bigger gear is the better solution as EPO is too expensive😊
KMC quick links are reusable. It's SRAM one's that aren't. 10 speed KMC quick links are difficult to remove without a tool.
No need to remove a chain to clean it if you look after it properly. I don't remove mine .
By the way you shouldn't use a KMC quick link on a 10 speed Shimano branded chain, even though KMC make Shimano chain. It works with 9 speed, but 10 speed Shimano chains are "directional" a gimmick but one that means the split link will be slightly different than the rest of the chain and that's not good. Once the Shimano chain wears out (usually very quickly) replace with the best quality KMC chain you can afford and look after it, they last for 10-15000kms if looked after.

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Post by martin mc » 27 Apr 2016 18:47

I've run 28 tooth rear cassette with short cage shimano 10 speed rear derailleur & compact chainset without problems, I didn't need to replace chain as length was fine. I have also run shimano 10 speed chain with kmc removable link without problems, didn't know there was an issue until Pete mentioned it here.

John D
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Post by John D » 27 Apr 2016 19:51

petemarshall wrote:Chain length should be set at big ring to big ring plus a link, without going through the derailleur. Any change in the sizes of rings will require you to change chain length. To short and it won't shift smoothly to long and you will drop the chain when changing down at the front.
If your cadence ever drops below 70 on a hill, you need a bigger gear or a bigger heart and lungs. I find the bigger gear is the better solution as EPO is too expensive😊
KMC quick links are reusable. It's SRAM one's that aren't. 10 speed KMC quick links are difficult to remove without a tool.
No need to remove a chain to clean it if you look after it properly. I don't remove mine .
By the way you shouldn't use a KMC quick link on a 10 speed Shimano branded chain, even though KMC make Shimano chain. It works with 9 speed, but 10 speed Shimano chains are "directional" a gimmick but one that means the split link will be slightly different than the rest of the chain and that's not good. Once the Shimano chain wears out (usually very quickly) replace with the best quality KMC chain you can afford and look after it, they last for 10-15000kms if looked after.
Pete
Chain is shimano 6701. I'll see how I get on with a kmc link (had a sram chain with kmc link on a 105 10sp groupset on my old bike without issue). I suppose I should invest in a chain checker and in fairness if it's having a replacement cassette, good time to replace the chain as well. Have struggled to remove a quick link previously but bought a removal tool which has saved time, knuckles and patience.

As regards chain length, never really gave it much thought previously but will check and probably order the longer length option to cover all bases

My Henry just made me smile as I'm tweaking the bike to fit, he said to make sure I do a m check before going out!!! Pleased to report he was paying attention last night.

Martin, guess proof of the pudding is in the eating. I'm keeping fingers crossed

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petemarshall
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Post by petemarshall » 27 Apr 2016 20:48

Never ever use a worn chain on a new cassette. If you look after the chain a cassette will see you through two chains. If you put an old chain on a new cassette it won't see you through one chain.
Chains usually come in standard sizes which are big enough to fit a 53 x 27 so big enough for anything you throw at a compact. You remove links to make them fit your set up.

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