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I'm thinking about replacing my rear derailleur which is a Shimano Acera with a Shimano Deore 9 speed. Is this a good derailleur? And one of my biggest questions is will it shift under loads well? For instance shifting to a larger sprocket while climbing. Also my cheap Acera needs constant adjustment after long rides (fyi the derailleur hanger isn't bent I checked it), will the Deore require less frequent adjustment?
 

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Probably not a huge difference between the two IMHO. Shifting under load is something you should almost never be doing. High revs equal quality shifts. Low revs equal exploded drivetrains.

Bill


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Yeah!
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Acera is a component group for casual riders (per Shimano). You won't notice a lot of difference between a NEW Acera and a NEW BOTTOM TIER Deore rear derailler, but Deore is more robust, and will retain accurate with good cables. Deore will have stronger cage springs to reduce chain slap, and higher tier models will employ shadow clutches. Deore is better suited for the demands placed upon components by trail riding.

Do NOT shift under load, no system is designed for that and it will damage your derailler, chain, chainring and cassette. Might be why the Acera needs constant adjustments, you've probably worn out the pins in the housing. Shift into the gear you need BEFORE a climb, and spin up so you can release pressure for at least two crank cycles to change gear if needed during a climb. With practice, you can make silent gear changes while climbing, and will know you are not tearing up your drivetrain.
 

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Deore 9-speed is an exponential improvement, over Acera. Wears unbelievably well too. Totally WORTH it....
 

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Just Ride!
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I have never found any system to shift well under a load and that is because they are not designed to do so. If you are needing constant adjustments on your current system, it most likely just needs a new high quality cable with a smooth run. And yes, I run two bikes with Deore and they shift perfect when the cables are new and the drivetrain is clean.
 
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