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I have a Scott E-Genius 730 Plus and would like to replace the rear dérailleur (the probable cause of difficulties described in my last question). It's a Shimano Deore SLX Dyna-sys unit, it's for a 10-speed cassette, and has a code RD-M7000 stamped into a metal part of the body. The drive system does not have a front dérailleur.

Shimano RD-M7000 Dyna-sys dérailleur

I have found a Shimano Deore M6000 Shadow+ 10 Speed Rear Mech, which I assume would fit. It asks me whether I want a medium or long cage, and I don't know.

I was hoping I could find a Bill Of Materials ("BOM") for my bike, perhaps by looking it up on the Scott website by its frame number, or scouring through the supplied CD-ROM and manuals. None of these have provided much information, other than basic brand information that I already know. I have also looked at the Shimano website, but this does not seem to provide measurements (e.g. see this product).

The cassette is 11t to 36t, so based on this answer I have these calculations:

  • Maximum Chainring Difference = 0 (there's only one chainring)
  • Maximum Cassette Cog Difference = 25
  • Total Drivetrain Capacity = 25
  • Maximum Cassette Cog = 36

Based on the Total Drivetrain Capacity, that would point to me being able to use either Medium or Long (my Maximum Cassette Cog exceeds the 34 limitation, but that answer is nine years old, and some comments indicate that 36 is pretty normal).

Of course Medium might be good in relation to ground clearance, but I might be tempted to go for Long if that's what I have already. What cage size do I have, and is there physical measurement data available that I could have used to answer this question for myself?

  • My latest research, since I commented under abdnChap's answer, is that I am leaning towards Long cage. There's two reasons for this; firstly, if one looks at the image, my existing dérailleur has around 5" of ground clearance, which may not be considered much on an off-road MTB. If I were running a Medium, then a Long would be maybe getting another inch closer to the floor, which would be cutting it fine. – halfer Jun 3 at 19:32
  • Also, I've done a search of the Shimano site, and only RD-M7000-10-SGS (Long) appears to be available in the 10 speed. I can get a RD-M7000-11-GS (Medium) but it's an 11 speed. – halfer Jun 3 at 19:32
  • That's what used to be called a "long cage". Dunno what it's called now. – Daniel R Hicks Jun 3 at 21:33
  • @DanielRHicks: and I thought this problem was complicated enough ;-). – halfer Jun 3 at 21:38
  • Just to record something for posterity: an answer here recommended this resource on how to determine cage size from dérailleur pinion distance (centre to centre). It was deleted, I think because the information was discovered to be quite out of date. – halfer Jun 4 at 13:36
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I'm certain by the looks of it your current SLX der is an SGS, or long, cage. Referring to the Shimano Specification Chart one can see that the RD-M7000 is only available with the SGS length cage. This makes it a little more versatile, being able to handle 1, 2 or 3x drive trains. The long SGS cage is able to handle the large amount of chain wrap involved on a 3x drivetrain. It has a high total capacity in other words.

The Deore RD-M6000 is a nice derailleur too. I've seen on eBay some excellent deals on them. And brand new as well. Product endorsement is shunned here on Stack Exchange, however, one can find several objective areas to support the viewpoint that Shimano has an outstanding record of quality and value.

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  • Thanks, I appreciate the confirmation of my suspicion that the RD-M7000 is not available in a Medium. That helps. My cursory searches today indicate that I might have to import it into the UK, and although that's not a problem with eBay, it pushes up the price and I wonder if the delivery might be more complicated given the pandemic. Would you have any confidence that I could use the RD-M6000? My usual seller has this in stock (though only the Medium and not the Long). I am happy to push for a RD-M7000 if it is thought to be the best chance of fitting my bike. – halfer Jun 3 at 22:20
  • (I agree about Shimano quality - where a bike already has Shimano components, I wouldn't fit anything else.) – halfer Jun 3 at 22:22
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    @halfer The M6000 would be a drop in replacement. Technically, it would be downgrade only that SLX sits one rung above Deore. However, there is little to no difference in quality or material. The Deore line has a long history of high quality and performance and the name is also given to the second highest level of mountain components, the Deore XT line-up. The M6000 also has a choice of GS or SGS cage lengths, as you've noted. – Jeff Jun 4 at 3:26
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    @halfer Just prior to changing their model numbering system, the Deore Shadow rear der carried the model # RD-M610. Check out the value of these babies. Sometimes they'll hit $19.99 USD. – Jeff Jun 4 at 3:43
  • Great advice Jeff, thanks. That gets me out of two days of component head-scratching! – halfer Jun 4 at 11:31
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That linked answer is great, but the lengths of derailleur cages have been increasing with successive generations, so those figures are out of date now.

You need to consider the size of largest cog which the derailleur is compatible with and compare the specs of the individual units.

Counterintuitively, the longer cage is actually compatible with the 36 tooth large cog you have, even though this 36 is smaller than many around today. The medium cage M6000-GS is suitable for cassettes where the largest cog is a 42T, while the long cage M6000-SGS works with cassettes where the largest cog is in the range 32-36 teeth. If you were choosing between these two, then you would choose the SGS long cage

There's every likelihood that your bike currently has the RD-M7000-10-SGS for the same reason (also its the 10 speed one).

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  • Thanks Swifty, this is the direction I was leaning in. So much confusion would be saved if Shimano had stamped the cage size on the product! From my research it appears that the RD-M7000 is not available in a Medium cage size for the 10 speed, but is if I were running 11 speed. Phew! – halfer Jun 3 at 21:08
  • It sounds like the M6000 (Medium) might also work then, given that my largest cassette cog is the 36T. Though I wonder if I should just plump for the M7000 (Long) just to be on the safe side, I notice that my usual supplier has mediums in stock at present, and they're 30% cheaper (due possibly to a fairly random pricing strategy). – halfer Jun 3 at 21:10
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    I'd add to Swifty's contribution that the larger cog tooth capacity of the GS cages is because they are to be used in 1 or 2x drive trains where the front chainwheel tooth difference is lower, thus saving some chainwrap room for the larger number of teeth in the rear. The shorter cage has more ground clearance also which comes in handy on the terrain for which the super low gears are used. – Jeff Jun 3 at 22:15
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I found this very well articulated answer for you, which I feel lays out how to determine the right size for your drive train. https://bicycles.stackexchange.com/a/7265/47206

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    Thanks, I appreciate the help - but I referred to that answer in my question ;-). The calculations in that answer showed that the Maximum Cassette Cog for both GS and SGS is 34, but I have 36. A comment underneath from "cherouvim" notes that 36T on MTBs is pretty normal these days. So, I wonder(ed) if this is out of date. – halfer Jun 3 at 19:30
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    I've added some more notes under the question. I am leaning towards Long at the moment, though any comments on that are still welcome. – halfer Jun 3 at 19:32

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