New rear derailleur advice



Goshawk

New Member
Apr 26, 2011
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yesterday my old shimano RD M330 failed very badly at high speed :( im looking for an upgrade and replacement part for it, its from an old carrera virtuoso road bike, ive got about £50 to spend on an 8 speed replacement any suggestions as to what i could get
 
The derailleur you mentioned (RD-M330) is listed by Shimano as an Acera derailleur. Compatibility in RDs has two components:
  1. The width of chain you can use (also determines the number of speeds) and
  2. the size range of the sprockets themselves.

In terms of point 1, a 2200 or a Sora derailleur should do as a replacement. 8 to 9 speed is no big difference in compatibility or actuation ratio.

As far as point 2 goes, you haven't really said what kind of gearing you're running. The Acera is actually an MTB derailleur and has a pretty long cage capable of accommodating a broad range of sprocket and chainring sizes.

To be completely accurate every RD has a rated "capacity" (available on shimano's tech info). To calculate the required capacity:
  1. Find the difference between biggest and smallest chainrings (for a 39/53 this is 14)
  2. Find the difference between the biggest and smallest sprocket (for a 11-27 this is 16)
  3. Add these together (in this case it is 30, and this set-up will math with a SS type derailleur which has a capacity of about 30)

As a rough estimate: The Sora and 2200 should come in short cage (SS) or long cage (GS) versions. Both versions can accommodate a cassette with a small sprocket of 11T and a maximum of 27T. The SS will suit double front chainrings and the GS will suit a triple.

If you have bigger sprockets you may have to go to another MTB derailleur.
 
hey thanks for the reply and sorry for the really late reply on my behalf looking at the actual cassette its an SRAM 40Nm im reallly new to all this so im sure ive more than likely found the wrong info :( looking at the actual derailleur it looks to be fairly long compaired to ones ive found browsing around, my biggest problem seems to be that all road ones ive found dont go to 8speed that all seem to be 10+ more than likely because my bikes hitting about 3 years old now, the front gears are 2 chainring along the front although at closer inspection they seem to have gone from round to rugby ball style shape :S so i might have to replace that as well
 
Goshawk said:
hey thanks for the reply and sorry for the really late reply on my behalf looking at the actual cassette its an SRAM 40Nm im reallly new to all this so im sure ive more than likely found the wrong info :( looking at the actual derailleur it looks to be fairly long compaired to ones ive found browsing around, my biggest problem seems to be that all road ones ive found dont go to 8speed that all seem to be 10+ more than likely because my bikes hitting about 3 years old now, the front gears are 2 chainring along the front although at closer inspection they seem to have gone from round to rugby ball style shape :S so i might have to replace that as well
The 40Nm isn't a model number - it's how tight you need to torque the lockring. The other set of numbers on there will likely be the model number.
 

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