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Using two different cassettes on road bike w/ mtb rear derailleur

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Using two different cassettes on road bike w/ mtb rear derailleur

Old 10-21-13, 03:22 PM
  #1  
jetter
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Using two different cassettes on road bike w/ mtb rear derailleur

I recently replaced the 12-27 cassette on my road bike, with an 11-34 mtb cassette. I also had to swap out my rear derailleur with a 10speed Deore MTB rear derailleur w/ long cage to fit the larger cogs. 90% of my rides involve extended climbs and I rarely only bike on flat, so this why I made the change.

I just purchased a bike trainer, and I don't really want to use my nice tires on it due to wear, so I'm going to use an older wheel w/ a tire i don't care about.

Here's my question:

If I use my original 12-27 as the cassette on my old wheel for training, will my 10speed MTB rear derailleur and chain work without any problems? I don't see why it wouldn't work since I'm already using almost all the same cogs on the 11-34 cassette. I just wanted to be sure this wasn't going to mess anything up.

Thanks!
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Old 10-21-13, 03:32 PM
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Originally Posted by jetter View Post
I recently replaced the 12-27 cassette on my road bike, with an 11-34 mtb cassette. I also had to swap out my rear derailleur with a 10speed Deore MTB rear derailleur w/ long cage to fit the larger cogs. 90% of my rides involve extended climbs and I rarely only bike on flat, so this why I made the change.

I just purchased a bike trainer, and I don't really want to use my nice tires on it due to wear, so I'm going to use an older wheel w/ a tire i don't care about.

Here's my question:

If I use my original 12-27 as the cassette on my old wheel for training, will my 10speed MTB rear derailleur and chain work without any problems? I don't see why it wouldn't work since I'm already using almost all the same cogs on the 11-34 cassette. I just wanted to be sure this wasn't going to mess anything up.

Thanks!
If the Deore derailer is a Dynasys, it won't work with shifters other than Dynasys. A 9 speed Deore (or any mountain derailer in 9 speed) will work with 6,7,8,9,10 road shifters.
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Old 10-21-13, 03:39 PM
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You're just asking about throwing a 12-27 cassette on your wheel and using your bike as it otherwise is? Should work fine.
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Old 10-21-13, 03:40 PM
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Originally Posted by cyccommute View Post
If the Deore derailer is a Dynasys, it won't work with shifters other than Dynasys. A 9 speed Deore (or any mountain derailer in 9 speed) will work with 6,7,8,9,10 road shifters.
Ok, you're right. I do have a 9 speed derailleur. I remember that being an issue.
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Old 10-21-13, 03:41 PM
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Originally Posted by ThermionicScott View Post
You're just asking about throwing a 12-27 cassette on your wheel and using your bike as it otherwise is? Should work fine.
Ok, thanks! It seemed like an obvious answer, but just wanted to make sure I wasn't overlooking anything.
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Old 10-23-13, 07:42 PM
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Since (a) you're going down in cassette range, and (b) the smallest cog in the 12-27 is larger than the 11-34, there shouldn't be an issue. You might need to tweak the B screw to move the rear derailleur vertically away from the cassette if it was set up particularly close.
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Old 10-23-13, 09:10 PM
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There are sometimes a need to slightly change the der limit screws when changing wheels (or cassettes). Andy.
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Old 10-24-13, 05:23 AM
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Since you are using this on a trainer, I wouldn't worry too much about perfect shifting either. Just make sure the upper limit screw doesn't go past the large cog. That shouldn't be a problem, but check it. Just put the wheel on, put the bike on the trainer, and try it out. Nothing terrible will happen.
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Old 10-24-13, 07:49 AM
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There may be too much chain slack in your small-small combo when you swap back to the 12-27 cassette from the 11-34 without also swapping out to a shorter chain. Or, if you did not swap chains when you went up with the cassette, you may want to stay away from your big-big combo with the 11-34 installed.

Were I in your situation and swapping cassettes more than it appears you intend to, I'd use a chain cut for the 12-27 cass, add in 2-4 links with quick connectors to get it right for 11-34, and adjust the chain as cassette swap demands.
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Old 10-24-13, 08:44 AM
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Originally Posted by mconlonx View Post
There may be too much chain slack in your small-small combo when you swap back to the 12-27 cassette from the 11-34 without also swapping out to a shorter chain.
There will be slightly less slack in small-small with the 12-27 than in small-small with the 11-34.
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Old 10-24-13, 09:50 AM
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Chain wears in , so pull off the chain and bag it with the cassette,

and get a new chain with your alternate cassette.

& when you change back, change both..
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Old 10-24-13, 10:21 AM
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Originally Posted by CACycling View Post
There will be slightly less slack in small-small with the 12-27 than in small-small with the 11-34.
No, there won't.

Not if the chain was properly replaced or links added in when the 11-34 cassette was installed.

If the original chain was used, you are correct, but then there's a good chance the derailleur will bind up in the big-big combo.
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Old 10-24-13, 12:29 PM
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Originally Posted by mconlonx View Post
No, there won't.

Not if the chain was properly replaced or links added in when the 11-34 cassette was installed.

If the original chain was used, you are correct, but then there's a good chance the derailleur will bind up in the big-big combo.
Having the chain on an 11 tooth rear cog will result in a slightly slacker chain than it being on a 12 tooth cog.
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