• 12-08-2015
    p08757
    Cassette Replacement Question
    I'm in the process of rebuilding my commuter road bike. I've basically stripped the entire thing down to the frame, which is being powder coated this week. I need to replace my cassette which is currently a 12-25 Shimano 9 speed. I would like a bit lower gearing for hill climbing, and my question is: How much bigger can I go with my cassette? Would something like an 11-32 9 Speed be too large?

    Thanks for any feedback.
  • 12-08-2015
    jeffscott
    it is very unlikely a bigger granny sprocket on the rear cassette will interfere with the frame tire or derailleurs...

    Need to do a tooth count to establish the required length of the derailleur arm...
  • 12-08-2015
    blkangel
    What derailleur are you using now? That will determine if a new derailleur is required.
  • 12-08-2015
    Volsung
    Shimano 9 speed road and mountain are compatible with each other, so find an older Deore or XT and go as big as you want.
  • 12-08-2015
    CommuterBoy
    Yeah, that's a derailleur question, not a cassette question. Cassette granny ring can be as big as your derailleur can handle.
  • 12-08-2015
    watts888
    Any idea what derailure you have, and how many chainrings do you use up front?

    Agree with above. also want to check chain length. If you're getting a new chain (which you should do if you're getting a new cassette), not a problem. If you're breaking all the rules and keeping your old chain, it might not be long enough because of the increased cog size.

    In summary, get a new chain too.
  • 12-08-2015
    p08757
    I don't have the derailleur in front of me right now, but off the top of my head its a Shimano Tiagra 9 Speed. Also note this is a road bike (old Giant OCR 2) and not a MTB.

    I will also be replacing the chain along with lots of other various parts that are all used up.
  • 12-08-2015
    watts888
    Quote:

    Originally Posted by p08757 View Post
    I don't have the derailleur in front of me right now, but off the top of my head its a Shimano Tiagra 9 Speed. Also note this is a road bike (old Giant OCR 2) and not a MTB.

    Looks like you might need a new derailleur then. Have to verify the model number, but it looks like 27T is the max cog size. Worst case, get a deore 9-speed mountain derailure and go up to 32 easily. As mentioned, same road shifter will work with a rear mountain derailure, so it's an easy swap.

    http://www.shimano.com/media/techdoc...9830607047.pdf
  • 12-08-2015
    bedwards1000
    You are interested in the cage length of the derailleur which will determine it's "capacity". If it is a short cage road derailleur then it might not work but if it is medium or long it should. Here is some info on determining the capacity.
    Understanding Rear Bike Derailleurs - Performance Bike Learning Center.

    Worst case you can try it. Break the chain so it fits over the large/large combination through the derailleur with just a little extra and then shift to small/small and make sure there is no slack (droop) in the chain. Even if there is you can avoid that gear. Or you can spend about $35 on Jenson and get a new one.
  • 12-08-2015
    CommuterBoy
    1 Attachment(s)
    Quote:

    Originally Posted by p08757 View Post
    (old Giant OCR 2)

    Memories...Attachment 1034452
  • 12-08-2015
    p08757
    Quote:

    Originally Posted by CommuterBoy View Post

    That looks like a 2001. Mine is a 2003: