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Long cage MTB derailleur with road (11-25) cassette?

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Long cage MTB derailleur with road (11-25) cassette?

Old 11-09-12, 09:45 AM
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Long cage MTB derailleur with road (11-25) cassette?

I'm installing a long cage MTB derailleur on my road bike with a 11-36 cassette to try out on some mountain time trials next year.

Will I still be able to use the long cage derailleur with the old 11-25 cassette? In other words - can I feel swap the 11-36 and 11-25 cassette without having to install the old derailleur again? Or will everything be off?
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Old 11-09-12, 10:08 AM
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What speed is your setup, and in a why, what the point?

Reason for what's the point question, is, your going to need to have a separate chain if using a 11-36 cassette, as it will be far to long for use on a 11-25 cassette as well, you already have a RD which works with your current 11-25, if your swapping cassette & chain, swapping the RD back as well isn't a big deal.
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Old 11-09-12, 10:10 AM
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the distance between 'speeds' is the same ? both 10,or 9?

guess: it will be adequate , But the chain wear, wore the old cassette.

and you will need a new chain, to fit around the 36t..
so thereafter, if you put the old 25t cassette on there would ,
potentially be a wear mismatch.
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Old 11-09-12, 10:12 AM
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Originally Posted by aaronechang
I'm installing a long cage MTB derailleur on my road bike with a 11-36 cassette to try out on some mountain time trials next year.

Will I still be able to use the long cage derailleur with the old 11-25 cassette? In other words - can I feel swap the 11-36 and 11-25 cassette without having to install the old derailleur again? Or will everything be off?
The issue isn't the cassette size, but the compatibility of the levers and derailleur. As long as they have the same cable response ratio, you're fine using the long cage RD. The only significant drawback is lower ground clearance on the right side, so watch yourself when sneaking through a gap between two rocks.
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Old 11-09-12, 10:22 AM
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Originally Posted by jimc101
your going to need to have a separate chain if using a 11-36 cassette, as it will be far to long for use on a 11-25 cassette as well,
I don't understand this argument. I'm thinking that a "too long" chain would be defined by the little/little gear combination. That's going to be the same whether you're using an 11-25 cassette or a 11-36 cassette.
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Old 11-09-12, 10:46 AM
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Thanks for the responses. I'm ok with changing the chain every time I swap cassettes - I just didn't want to go through the hassle of uninstalling / reinstalling a new derailleur.

About the 9 / 10 speed compatibility - I'm using Ultegra 6700 10-speed shifters, and according to my research (and according to a few older threads here on BF) any Shimano 9-speed MTB derailleur will work with the 10-speed road group. I plan on using an XT-M772 long-cage derailleur with an XT 10-speed 11-36 cassette. Apparently Shimano's new XTR 10-speed MTB derailleurs will not work with the 10-speed road shifters.

About the why / what's the point - I ride at a pretty high cadence (100+) and am most comfortable climbing at around 90 rpm. I've been practicing on some 7% grades (parking garages - there are no hills in Houston) on my 34 / 30 road setup and it's acceptable but I would prefer something a bit lower. At 34 / 30 on a 7% grade I'm around 75-80 rpm. I'm planning on swapping out my 34t for a 38t for a better usable gear range for daily riding, and I calculated that a 38 / 36 would give me something a step lower than the 34 / 30 I've been working with. Yes - I could just put on a triple front crankset but that would require getting a new fit / crankset + power meter / rearrange cleats, etc. etc.

I talked to some guys at the local LBS and they hinted that I might have problems with the long cage derailleur and the 11-25 - that it would "work ok but not work well". That's why I was wondering if there were any shifting issues with the long cage RD and road cassette. If the only thing I need to worry about is lower ground clearance, that's fine - I'll be riding on the road and not off-road.
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Old 11-09-12, 10:51 AM
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You may want to "tweek" the "B" screw adjustment when switching between cassettes to optimize shifting.
It probably won't be "correct" with the "road" cassette, but since the jumps between cogs is less, you shouldn't have any shifting problems.
I'm using a Tourney & Acera on my two 9 speeds (12-21 & 12-23) and they shift fine.
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Old 11-09-12, 11:48 AM
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Originally Posted by Retro Grouch
I don't understand this argument. I'm thinking that a "too long" chain would be defined by the little/little gear combination. That's going to be the same whether you're using an 11-25 cassette or a 11-36 cassette.
Exactly, RG. You can bet that one of the cogs in the 11-36 cassette is a 24 or 25... and if it works for that, it should be just fine.
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Old 11-09-12, 12:43 PM
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aaronechang, You won't have any problems. A new, longer chain most likely will required to account for the extra links within the longer cage and to avoid the possibility of pulling the RD into the spokes using the big/big combo.

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Old 11-09-12, 02:57 PM
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Your long-cage derailleur should work fine with the smaller cassette although shifting may be slightly less snappy but still acceptable. You should readjust the B-screw when you switch cassettes. You don't absolutely need a shorter chain with the smaller cassette although keeping a chain with its respective cassette will minimize wear caused by a single chain "wearing-in" to different cassettes and a shorter chain may slightly improve shifting of the smaller cassette.

You won't need a longer chain with the long-cage derailleur. Consider that when you size a chain using the "big-big" chain sizing method the derailleur is not even a part of the length determination and this method results in the shortest chain length of the common methods. So any method will result in a "long enough" chain. If the derailleur will work with the small cog of the 11-36 cassette it will work with the same size cog of the 11-25.
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Old 11-09-12, 04:08 PM
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Originally Posted by bradtx
A new, longer chain most likely will required to account for the extra links within the longer cage and to avoid the possibility of pulling the RD into the spokes using the big/big combo.

Surely having the chain too short won't pull the derailleur into the spokes? I'd have thought it'd just rip the bloody thing off if you went into a combination where you didn't have enough chain? Admittedly, that's just as bad for the derailleur, the hanger and potentially the frame, but at least the wheel tends to survive...

Edit:

Originally Posted by dsbrantjr

You won't need a longer chain with the long-cage derailleur.
No, but running a larger rear sprocket will normally necessitate a longer chain, and this whole thing is being done in order to get larger cogs on the rear....

Last edited by Airburst; 11-09-12 at 04:11 PM. Reason: typo
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Old 11-09-12, 04:16 PM
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A standard mtb / touring cassette is 11-34... 36 tooth cogs come with cassettes designed for 29r bikes and have a specific hub that is stronger to withstand the extra torque and running these on a standard hub may cause failure.

The chain used for the 11-34 / 36 will work with the 11-25 but not vice versa... if you set this up I would run two chains and pair them with their respective cassettes to get the optimal length for each cassette and to prevent mismatches in wear between the chain and cassette. The wider range block and longer chain will work with the 11-25 road cassette if you are running the long cage rear d but shifting performance will be degraded slightly.

Have run bikes like this where I wanted to switch from a closely stepped road block to a wider range Alpine block to suit the riding conditions and the swap does not take much time at all.
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Old 11-09-12, 04:29 PM
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Originally Posted by Sixty Fiver
A standard mtb / touring cassette is 11-34... 36 tooth cogs come with cassettes designed for 29r bikes and have a specific hub that is stronger to withstand the extra torque and running these on a standard hub may cause failure.
As in ratchet failure, or freehub spline failure? I'd assume ratchet?
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Old 11-09-12, 05:02 PM
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"No, but running a larger rear sprocket will normally necessitate a longer chain, and this whole thing is being done in order to get larger cogs on the rear.... "

Correct, but my point is that chain length is dictated by the large chainwheel/large sprocket size not the derailleur cage length. The derailleur cage configuration determines the chain wrap capability.
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Old 11-10-12, 09:59 AM
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Personally, I wouldn't be concerned about the increased stress on the freehub as I'm an average strength 165 lb roadie. For a strong 200+ lb rider, it might be more of a concern. SRAM markets their "WiFli" 32 tooth road groups with no weight restrictions that I'm aware of.
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