Shimano mtb chainrings

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  • I tried posting in the current projects thread (­72) but figured this is quite a specific issue. Does anyone know which (larger) chainring I can use to increase the tooth count of a 44t Shimano Deore LX? I'm confused, to say the least. I'm guessing a Shimano FC-M530 (48t, 9 speed, 104BCD) but then there is FC-M590, FC-M510, FC-M660, and that's not including other manufacturers like Blackspire, Truvativ or the Specialites TA versions. I found a 48t Chinook with the right BCD but don't know if I will need to make any changes to the chain, or derailleur, cassette or bottom bracket? I read that it may only be possible if I change all three chainrings to keep the differences equal (22/32/44 to 26/36/48) but that sounds prohibitively expensive. I feel I may be opening a can of worms here...

    Anyone able to assist/put me out of my misery?

  • Anyone?

  • You’ll need to look into the capacity of the front mech to know how much larger than the little ring you can go.

    As for the chain, stick the bike in the big cog at both ends and see what position the rear mech cage is in. You might need to add a link or two but might get away with it if it’s only a couple of teeth and the chain isn’t too short at the moment.

  • Thanks for that, I'm not sure about the rear mech, looks pretty stretched as is. Not sure about the front mech either, I'm guessing it can be moved to accommodate a bigger ring but it may be a lot of effort for minimal impact. What do you reckon?

    So hot here today! 🥵

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  • Is that your current setup? That rear mech already looks far too stretched as it is let alone with a bigger chainring. Did it come like that it did you set it up? The front mech actually looks too high above the large chainring (gap between large chainring and bottom edge of front mech cage should be about 1-2mm).

    Anyway, look up the specs of your derailleurs and see what the max tooth capacity is. If the extra teeth you want to put on the front chainring is still
    within their capacity then you can just change the big ring and leave everything else as it is, apart from the chain which needs more links.

    (Any 4 hole chainring with the right BCD will work)

  • Would agree with that.

    Chain is too short already and mech too high.

  • I had it setup by the guys from Pinarello, but only the fitting of the chain (a new KMC one I bought when I picked up the bike) and they told me they had indexed the gears too. I thought it looked a bit off with the mech in that position. I'll take it back in the week and see what they say. If the front mech won't allow it, I guess I can swap it for one that can accommodate 48 teeth?

  • I think the image shows the front mech specs.
    And from stack exchange (rear derailleur):
    "Looks like it only came in an SGS (long) cage version.

    Total cap: 43
    Max front diff: 22
    Large sprocket max: 34
    Small sprocket min: 11"

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  • Mmmmmm, really want that gold groupset!

  • @yoav @M_V I've been back to Pinarello this afternoon, the mechanic had a look and explained that I cannot add length to the chain as if I do, it'll be far too slack when in the granny gears (photos to illustrate). He was concerned about moving the front mech as, in his words, "if it works, it works". It's as if the spread of gears are far too wide: I never use the smallest chainring (22t), and hardly use the medium (32t). In the big ring (44t) I'm shifting between 2 or 3 of the top gears and that's it, depending on the speed/terrain. On recent rides, I'm averaging about 35kph and that's on gravel, without really hammering it. I'm at a loss to understand.

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  • What the range of your rear mech (from the specs sheet) and what is the range of your cassette?

  • The specs below are for the rear mech (RD-M570) and the cassette is 11-32 ( CS HG50). Looks like total capacity 43t, largest sprocket 34t, smallest 11t, front chainwheel tooth difference 22t.

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  • In that case you are right on the limit. For a bigger front ring you’ll have to sacrifice something, either your little front ring or your largest rear cog.

  • What size is the cassette?

    If it’s an 11-32 or some wide range like that then yeah, combined with the 22-44t range up front the gear range could be too much for the rear mech to handle.

    You’re already at the 22t difference that is the most the front mech can handle so to get a bigger gear you’re either going to have to ditch the granny ring or get a new front mech that can handle a wider range (if that exists).

    I’d probably:

    Fit a cassette with a smaller large cog. That’ll stop the mech being so stretched out and give you more gears in the range you’re using.

    Ditch the granny ring.

    Fit a larger outer chainring.

    Set up the front mech and shifter as if it was a road double and just not use the third click.

    If you ditch the granny of course you’ll have the issue that you’ll be cross chaining a bit more so you might want to think about a new, shorter bb or moving some spacers around if it’s ht2.

    Oh but first I’d find a new mechanic, one that’ll set a mech up in the right place, not just leave it where it is “because it works”.

  • @M_V and @yoav thank you very much for your replies. Yes, I need a new mechanic - I only use these guys infrequently as I prefer to try and do as much work as I can on my bikes, to help me learn, but there are some jobs that are beyond me due to a lack of tools.

    I'll buy an 11-28 cassette (Shimano CS-HG80) and try that first. If I find I need to make more changes, I'll look at removing the smallest ring and increasing the size of the largest, but for now I think the cassette swap is the best option, especially as I don't know how old this one is. Thank you both again!

  • ...Or give up and sell me the groupset, always good to have options 😜

  • Don't tempt me! I must admit the thought of simply running this as a single speed is becoming more pleasing with every passing minute (albeit, there is no fun in taking the easy way out).

  • This looks like the perfect frame for the headset the forks and headset on that Pace @jambon

  • Very true! I passed on the Pace, wheels couldn't be destickered so passed.

  • You want to add extra colour to this?!

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  • That's a lot of logo on the seatpost.

    Got a pic of the brakes?

  • @psg1ben haha, it's new too. Just haven't been bothered to try and remove it.

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Shimano mtb chainrings

Posted by Avatar for MrMister @MrMister