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Why do rear derailleurs have a spec for max chainring difference?


brucem76

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Do you ride up walls?

 

24/42 is just a ridiculous ratio!

 

Sorry, I am adding nothing of value to this thread, just trying to figure out what cadence is needed to stay upright moving at 0.0004kph

 

(I am being that guy today... sorry)

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I already have 11-42 with 24-38 with a Deore M610 SGS long cage, but shifting is horrible....

 

Sent from my Redmi Note 3 using Tapatalk

 

Define horrible from your point of view?

 

Have you had your LBS reset or realign your RD?

 

Is it horrible on ever gear shift or only when going from the big to little chain ring and vice versa?

 

I don't see why it should be a problem as the overall capacity is 43T as long as there is not too big a difference in the chain rings. The max difference on the M610 SGS is 22 and you are at 14! 

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I already have 11-42 with 24-38 with a Deore M610 SGS long cage, but shifting is horrible....

 

Sent from my Redmi Note 3 using Tapatalk

 

Recently I had some concerns re a 1x9 drive-train. I posted pictures of the RD in smallest and largest sprocket and the Hub, in all of its wisdom, sorted me in a jiffy. It might be worth posting some pics of your extreme shifting situations for some comments? Just a suggestion.....

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Do you ride up walls?

 

24/42 is just a ridiculous ratio!

 

Sorry, I am adding nothing of value to this thread, just trying to figure out what cadence is needed to stay upright moving at 0.0004kph

 

(I am being that guy today... sorry)

Lol - bulk yourself up to 130kg, head up anything more than 12%, and get back to me :)

 

Sent from my Redmi Note 3 using Tapatalk

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Ok so I just did some reading on the total capacity of the RD and learn't something new  :P

 

To work out whether or not the RD will work with your selected ratio's you take your smallest sprocket (11) and subtract it from the largest (42) and add it to the difference in your chain ring sizes. So in your case 42-11+38-24=45!

 

From this you can see that you are exceeding the overall capacity of any 10 speed long cage RD as they all seem to have a limit of 43!

 

This will apparently cause the chain to be too slack in some gears and tight in others causing erratic gear shifting.

 

Your solution would be to reduce the chain ring difference to like a 38-26 or 38-28 or use an 11-36 cassette  :thumbup:

 

...or to help you on those hard uphills keep the 24 chain ring and drop the larger one to a 36!

 

To be honest if you want it to work properly you should use the components for which it was designed for and go the 11-36 cassette route  ;) 

Edited by Mr lee
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Define horrible from your point of view?

 

Have you had your LBS reset or realign your RD?

 

Is it horrible on ever gear shift or only when going from the big to little chain ring and vice versa?

 

I don't see why it should be a problem as the overall capacity is 43T as long as there is not too big a difference in the chain rings. The max difference on the M610 SGS is 22 and you are at 14!

But why do Shimano's specs say: "Maximum Sprocket Low sprocket 36T /Top sprocket 11T"??

 

Can't work out why there is a spec for max sprocket, surely the capacity should be all that's needed?

 

 

Sent from my Redmi Note 3 using Tapatalk

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But why do Shimano's specs say: "Maximum Sprocket Low sprocket 36T /Top sprocket 11T"??

 

Can't work out why there is a spec for max sprocket, surely the capacity should be all that's needed?

 

 

Sent from my Redmi Note 3 using Tapatalk

 

see my reply above

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But why do Shimano's specs say: "Maximum Sprocket Low sprocket 36T /Top sprocket 11T"??

 

Can't work out why there is a spec for max sprocket, surely the capacity should be all that's needed?

 

Might be due to the length of the upper part of the derailleur and/or the length of the b limit screw that it is shipped with. Either of these might result in insufficient clearance from the cassette with a 42t cog and then you end up grinding the top jockey wheel on the casette.

Edited by Jehosefat
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Merida Big Nine 500 2018 uses a 11-42 back 26-36 front Shimano Deore Shadow.

This would work because the difference is only (42-11) + (36-26) = 41 which is within the range pointed out by Mr Lee.

This bike must also be a serias wallclimber.

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Merida Big Nine 500 2018 uses a 11-42 back 26-36 front  Shimano Deore Shadow.

 

They have the new Deore M6000 components on there with a medium cage derailleur which has a largest sprocket limit of 42. The overall capacity of the medium cage is 41 so they are on the limit!

 

The M6000 long cage derailleur still has a large sprocket limit of 36 and is meant for applications where a larger chain ring difference is required or for 3x10.

 

The newage derailleurs are being designed to accept the now popular 42T cassettes so the older medium  cage derailleurs will not work as they have a 36T sprocket limit....irrespective of overall capacity.

 

And I am refering to 10 speed here, just in case the above is confused with the new 11 speed setups  :thumbup:

Edited by Mr lee
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@brucem76 - from what we now know you have the following options:

 

Change to an 11-36 cassette (cheapest!)

 

or...

 

Change to the new Deore M6000 medium cage rear derailleur and drop the largest chain ring to a 34T!

 

When I bought my bike just over a year ago it was 10 speed 11-36 / 36-22 and had a long cage RD....this before I went 1x11  :P . At the time I was around 126kg's and hardly ever used the 22/36 cause it was like pedaling in mid-air. As time went by, and the more I rode, I got fitter and lost weight. Now down to around 115Kg's.

 

With the 1x11 I do not have the bail out gears I used to have but I am still able to make most climbs and I am still getting better....and less tired at the top of the climb!

 

What I am trying to say is that you should not harp on an easy setup for now because you are more than likely going to grow out of it in the near future  ;)    

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