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Ultegra 52/36 to 46/36

Hi folks, I'm looking to replace a big 52t chainring with a more compact 46t, going for a 46/36 or potentially even 46/34 setup.

The 46t ring I found here https://www.mantel.com/uk/shimano-ultegra-r8000-chainring looks a bit different to the 52t ring currently on the bike.

Will I also need to buy a set of bolts to fit it, like here https://www.mantel.com/uk/shimano-r8000?

Any other potential issues re compatibility?

Many thanks for your insights.

Posts

  • super_davosuper_davo Posts: 510
    What's the current crankset?

    Assuming Shimano 4 bolt R9100/8000/7000 gen should be OK. Outer rings have ramping pins so if you don't use them with the right inner shifting can be off.

    But both 46 and 52 are designed to be paired with 36 (46 being a CX ratio) so in this instance, should be fine.

    For this reason a 34 wouldn't work as well but even that might still be passable (not a huge diameter difference between 34 and 36).

    If you're using an older gen crankset, get a 46 from that generation (width spacing will be off otherwise). Bolts should be reusable either way.

    If non Shimano, then none of the above applies, get a Stronglight or similar from SKS, will be much cheaper.
  • What's the current crankset?

    Assuming Shimano 4 bolt R9100/8000/7000 gen should be OK. Outer rings have ramping pins so if you don't use them with the right inner shifting can be off.

    But both 46 and 52 are designed to be paired with 36 (46 being a CX ratio) so in this instance, should be fine.

    For this reason a 34 wouldn't work as well but even that might still be passable (not a huge diameter difference between 34 and 36).

    If you're using an older gen crankset, get a 46 from that generation (width spacing will be off otherwise). Bolts should be reusable either way.

    If non Shimano, then none of the above applies, get a Stronglight or similar from SKS, will be much cheaper.

    Hi, thanks for your response.

    Current crankset is Ultegra R8000 52/36.

    I know that R8000 is also available in the compact 46/36 version (positioned as a CX setup), so, logically, I don't see a reason why it shouldn't be working when assembled from separate chainrings.

    I would have just bought a complete 46/36 crankset and put mine for sale, but I can't find it with the 165mm cranks, hence have to replace the chainrings individually on the existing crankset.

    My only hesitation is whether I'll need to buy a set of bolts separately (as per link below), as the front side of 46t looks different to 52t and it seems that it needs these extra bolts.

    As far as changing the 36t inner ring for 34t, this seems like a minor change intuitively... I found some old forum posts when folks swapped the 52/36 setup for 52/34 and reported no issues at all. The only thing I wonder is whether I'll need to shorten the chain after moving from 52/36 to 46/34 - any thoughts here?
  • You're losing 6 teeth going from 52 to 46. But 36 to 34 is only 2 links so I'd suggest taking 4 links out and seeing where the derailleur cage goes when on the cassette limits (46/big cog 36/small cog - which you shouldn't use anyway*) You can simulate that by lifting a few links off the chain ring and watching the derailleur cage move. Once you're happy then shorten the chain.
    I like to have my chain at a length where the cage is almost at its limit on small chain ring and maybe 3rd sprocket at the back. As long as it isn't so short to seize up if (accidentally) going big/big!
    *Work out your gear inches and you'll see the overlap that can be avoided by only using part of the cassette for either chain ring.
    And you may well have to lower the front mech 1/2" or so, which might not shift quite as well because the 46T c/ring is a different radius and the mech will be matched to the 52T one.
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