Cassette for R8000 GS Rear Mech

bmxboy10
bmxboy10 Posts: 1,958
edited March 2019 in Road buying advice
Just got a new bike and it has the Ultra R8000 long rear mech with 11/32 cassette. Can I change this to a 11-25 or 11-28? I guess I just need to shorten the chain length or is there more to it than that?

Comments

  • N0bodyOfTheGoat
    N0bodyOfTheGoat Posts: 6,065
    The short 7000 and 8000 mech officially supports up to 11-30 iirc, you may find your long mech with 11-25 and possibly even 11-28 may not tension the chain that well in your easiest gear.

    What chain set rings does the bike have?
    What sort of gradient hills do you expect to ride on?

    You might get a few quid for selling a basically unused mech and cassette, but replacements in 8000 group would cost you ~£105, while in 7000 group ~£75.

    While a smaller range cassette will give you more chance to find a gear that works around your preferred cadence on the flat, especially if you're just starting out with a nice spec road bike, it might be better to spend that money on say a nice pair of tyres such as Continental GP4000S IIs; water bottles plus cages etc.
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  • bmxboy10
    bmxboy10 Posts: 1,958
    NitrousOxide wrote:
    The short 7000 and 8000 mech officially supports up to 11-30 iirc, you may find your long mech with 11-25 and possibly even 11-28 may not tension the chain that well in your easiest gear.

    What chain set rings does the bike have?
    What sort of gradient hills do you expect to ride on?

    You might get a few quid for selling a basically unused mech and cassette, but replacements in 8000 group would cost you ~£105, while in 7000 group ~£75.

    While a smaller range cassette will give you more chance to find a gear that works around your preferred cadence on the flat, especially if you're just starting out with a nice spec road bike, it might be better to spend that money on say a nice pair of tyres such as Continental GP4000S IIs; water bottles plus cages etc.

    Cheers - I thought it might be more technical than just changing the cassette. I hate having large increments between gears but since the bike cost quite a bit I think ill stick with what I've got for now at least.
  • bmxboy10
    bmxboy10 Posts: 1,958
    Just looked on Evans, Sigma and Merlin and they all say the GS is fine on 11-28 so looks like I'm in luck.
  • whyamihere
    whyamihere Posts: 7,716
    It will work fine. You'll probably want to tweak the B tension screw to bring the derailleur closer to the cassette when at the lower end of the cassette.
  • StillGoing
    StillGoing Posts: 5,211
    BMXboy10 wrote:
    NitrousOxide wrote:
    The short 7000 and 8000 mech officially supports up to 11-30 iirc, you may find your long mech with 11-25 and possibly even 11-28 may not tension the chain that well in your easiest gear.

    What chain set rings does the bike have?
    What sort of gradient hills do you expect to ride on?

    You might get a few quid for selling a basically unused mech and cassette, but replacements in 8000 group would cost you ~£105, while in 7000 group ~£75.

    While a smaller range cassette will give you more chance to find a gear that works around your preferred cadence on the flat, especially if you're just starting out with a nice spec road bike, it might be better to spend that money on say a nice pair of tyres such as Continental GP4000S IIs; water bottles plus cages etc.

    Cheers - I thought it might be more technical than just changing the cassette. I hate having large increments between gears but since the bike cost quite a bit I think ill stick with what I've got for now at least.

    Don't follow that advice! The GS mech is fine with smaller cassettes. I run it with 11-28 and 11-25. As long as the chain length is set correctly, you won't have any problems. Incidentally, the GS mech will take a 40 tooth sprocket too with adjustment to the B screw, so don't sell the mech.
    I ride a bike. Doesn't make me green or a tree hugger. I drive a car too.
  • keef66
    keef66 Posts: 13,123
    I had a 12-25 cassette with an older 5600 long cage rear mech and a triple chainset with a 30t inner ring. It managed to keep adequate chain tension in the small / small combo.

    I'm guessing your R8000 mech will be similarly accommodating. You don't even need to shorten the chain. If you think about it, you already use a 25t sprocket. You're just losing the 2 bigger ones.

    You could tighten things up by taking out a chain link or two and adjusting the B screw, but it will likely work well enough just as it is.

    And if you have a super hilly ride coming up, you can just whack the 11-32 cassette back on

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