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Discussion Starter · #1 · (Edited)
Not sure if this is already out there, I had previously never been able to confirm that it would work, and had actually heard that it wouldn't, but it does. I installed a RD-M9000 11 speed rear derailleur on my bike, directly replacing my RD-M985 10 speed, and it shifts fine. Spacing is the same with a 10 speed XTR shifter. I have a 1x10 setup with a 42t Wolftooth cog, and I was running a OneUp RAD cage on my M985. The M9000 has the offset pulley position of the RAD cage built in, so it shifts to the 42t perfectly and still works well on the small cogs.

So this is another option for putting together a sweet shifting wide range 10 speed drivetrain, I don't think it is worth upgrading if you are running a stock 10 speed cassette. And the RAD cage is still cheaper unless you were going to buy a new derailleur anyway. This also bodes well for when current XTR tech trickles down to XT and SLX, getting a nice shifting wide range Shimano drivetrain will be simpler and cheaper than ever for those of us that find 11 speed to be overkill. Now if they would just make a 10 speed 11-42 XT cassette.
 

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This is more news for the fact that you could potentially just replace a shifter, cassette and chain and go 11-spd. w/o getting a new RD.
I've suspected this for some time, there's a chap on here called Ikomar who makes a 42t sprocket to add an extra speed to a 10 speed cassette making it 11 speed. He also mods a zee shifter to shift 11 speed. He also says that the shift distance is the same sprocket to sprocket.

If using an 10 speed rear mech why use an 11 speed chain?
 

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Discussion Starter · #6 ·
I was recently emphatically told in the XTR thread that 10-speed RD will not work with 11-speed cassettes. In my mind there is some truth to the argument "then why did they re-design the existing RDs?"
Well, I have a feeling that the old XTR derailleur would work, but just in a piss-poor manner. I think there is enough range of adjustment to hit the 11th cog. But the offset pulley is the biggest difference between old and new, and you would have to modify your old derailleur with a RAD cage to get decent shifting out of it. Stock 10 speed derailleurs just don't have the correct geometry to track a wide range cassette.
 

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Discussion Starter · #7 ·
Never going to happen. They won't go back and tweak a prior generation of parts. I doubt they'll even come out with 11-42 11spd. They're really set on the whole "rhythm stepping" thing and 35 or 36 to 42 is too big of a jump in their eyes.
Sure, but a fool can dream. I have gotten the stink eye from both SRAM and Shimano reps when bugging them about this very issue, it is painfully obvious that they have no interest in giving us what we want. But fine, they can piss off, at this point I would rather my money go to Wolftooth anyway, if only I didn't also have to buy the damn Shimano 11-36 too.
 

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Well, I have a feeling that the old XTR derailleur would work, but just in a piss-poor manner. I think there is enough range of adjustment to hit the 11th cog. But the offset pulley is the biggest difference between old and new, and you would have to modify your old derailleur with a RAD cage to get decent shifting out of it. Stock 10 speed derailleurs just don't have the correct geometry to track a wide range cassette.
I wonder if anyone has tried this? Ikomar says there are no issues shifting using a 10-speed SLX/XT rear derailleur with his 11th-speed 42t cog using XT cassette - especially so with RADr cage. The folks in the other thread I referenced did imply that a sprocket-to-sprocket shift distance in the new 11-speed XTR cassette is the culprit for why the new RD is required, but that may not be accurate information if no one has actually measured it...who knows?

At this point, the RD is the second-most expensive part of an 11-speed Shimano upgrade (after the cassette), and double the cost of an XTR shifter. I already have a RADr cage - buying a 11-speed XTR cassette + shifter would be a lot cheaper for now.

Of course, I still wouldn't get 42t. So there's that. Do I need to ask about 10-speed Shimano RD + RADr working with SRAM cassette? Oh boy.... :D
 

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dadamamabooboo
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I've suspected this for some time, there's a chap on here called Ikomar who makes a 42t sprocket to add an extra speed to a 10 speed cassette making it 11 speed. He also mods a zee shifter to shift 11 speed. He also says that the shift distance is the same sprocket to sprocket.

If using an 10 speed rear mech why use an 11 speed chain?
i've never played with an 11-speed drivetrain in person, so with my own eyes i don't know, but i'm sure plenty others here do. at any rate, there is a difference in shimano spacing between 10 and 11-speed cassettes, as small as it seems. but i'd guess it's the sole reason for the 11-sp chain:

the sprocket widths for both 10 and 11-sp are 1.6mm, but the built-in spacer widths are 2.35mm for 10-sp and 2.15 for 11-sp. caveat emptor keeping that in mind.
 

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Thanks for that info - sounds like the 0.2mm difference is within tolerance for the 11-speed XTR rear derailleur/shifter - at least in the short term. Now to confirm that using the 10-speed derailleur+RADr instead will also work.....possibly with SRAM cassette.......haha!
 

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Its not a matter of tolerance its a matter of how far the shifter cable pulls the derailleur for each click. BTW I also hooked up an 11 spd xtr der last night on a 10 speed cassette with a 40t (and a 10 spd shifter) and it works fine as expected, and much better than the non-RADR'ed 10 spd der I have been using. Just waiting for my 11 spd shifter in the mail now.
 

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dadamamabooboo
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without looking at the detailed shimano pdf, there must be a slight difference between the 10 and the 11-sp indexing to account for the difference in spacing between 10 and 11-speed cogs, as slight as it is (2.35 vs 2.15). on the other hand, it may just be that the difference is indeed negligible enough for the 11-sp rd here to work on the 10-sp cassette. obviously some of you have gotten it to work.
 

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Discussion Starter · #17 ·
without looking at the detailed shimano pdf, there must be a slight difference between the 10 and the 11-sp indexing to account for the difference in spacing between 10 and 11-speed cogs, as slight as it is (2.35 vs 2.15). on the other hand, it may just be that the difference is indeed negligible enough for the 11-sp rd here to work on the 10-sp cassette. obviously some of you have gotten it to work.
I think you are mixing up what makes a shifter, derailleur and cassette compatible. The derailleur doesn't know or care about spacing, it only goes where the shifter tells it. The shifter is indexed to match the cassette spacing. If any two derailleurs move the same amount for a given amount of cable pull, they are interchangeable on a basic level. The difference in cassette spacing matters not a bit in this application, it all comes down to the derailleurs pull ratio matching up. If there was any pull ratio difference at all the M9000 would not work for crap with the 10 speed shifter.
 

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dadamamabooboo
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I think you are mixing up what makes a shifter, derailleur and cassette compatible. The derailleur doesn't know or care about spacing, it only goes where the shifter tells it. The shifter is indexed to match the cassette spacing. If any two derailleurs move the same amount for a given amount of cable pull, they are interchangeable on a basic level. The difference in cassette spacing matters not a bit in this application, it all comes down to the derailleurs pull ratio matching up. If there was any pull ratio difference at all the M9000 would not work for crap with the 10 speed shifter.
you're right, i sure did..got it turned badly around earlier. was sick and didn't work today so must be working with just half my brain. back for more tylenol..
 
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