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Drivetrain 8/9 speed compatability

balkan_bozobalkan_bozo Posts: 3
edited May 2014 in Workshop
Hi all. The whole drivetrain on my road bike needs replacing, you can practically drive a bus through the gap between the chainring and the chain. It's a Shimano compatible setup. I'm just confused with the 8/9 speed compatibility. Is it correct that an 8 and 9 speed cassettes are interchangeable? And if changed to a 9 speed, does the shifter have to be replaced? (The shifter is a 'Shimano Sora').

The current components are an 8 speed cassette; derailleur is '9 speed' and the chainrings are '9/10 speed' (two chainrings). I didn't even look at the etchings on the components when I bought them, I just trusted the chap at Evans but I'm wondering if the mish-mash of the components is the reason why the shifting has never felt quite right.

Chainrings: how do I know if I need a 'compact' or a 'standard'?

Some pointers greatly appreciated! :-)


  • gozzygozzy Posts: 640
    You can fit 8,9 or 10 speed cassettes on the same hub, so yes they're interchangeable. However you'll need a shifter that corresponds to the number of speeds, so 8 speed cassette needs 8 speed shifter, 9 needs 9 etc. The shifters pull the mech a set distance that changes with number of speeds.

    You'll be ok switching to 9 speed with those parts. You'll need a new shifter, cassette and chain.
    Compact chainsets have 50/34 teeth, Standard generally have 53/39. Count the teeth on the rings or look for the numbers stamped on the ring somewhere.

    TBH, you probably just need a new chain and cassette, btw.

    Mish mash of components shouldn't affect the shifting too much, you probably just need to fine tune the shifting.
  • Ahh so the "compact" chainring indicates a number of teeth. Got it, thanks.

    And how often should the derailleurs be replaced? The bike has done around 11K miles since last replaced in all sorts of weather. The jockey wheels are certainly screwed, they make a whistling sound in certain gears (embarrassing, but great for unaware pedestrians about to cross the road without looking!)

  • MatthewfalleMatthewfalle Posts: 17,380
    Derailleurs, unless you are upgrading or changing speeds (ie 9 to 10 or any other variance) generally need changing once a decade or so (presuming normal use, no major crashes and not riding it through the sea). They are pretty resilient.

    The important thing is to keep them clean and make sure all the cables (inners and outers) are kept clean and lubed (I but Shimano ones from the LBS (about a tenner for gear and brake inners and outers) and will change them once a year.
    Postby team47b » Sun Jun 28, 2015 11:53 am

    De Sisti wrote:
    This is one of the silliest threads I've come across. :lol:

    Recognition at last Matthew, well done!, a justified honour :D
    smithy21 wrote:

    He's right you know.
  • gozzygozzy Posts: 640
    As above, the derailleurs should last for years.
    If you've not replaced anything for 11k then you are going to need a new chain and cassette, so while they're off you can remove both mechs and give them a good clean and lube up.
    Regular basic maintenance goes a long way.
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