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I need to change my chainring(s) and am interested to know what the things to pay attention to are. The ones that are clear to me are:

  • the number of holes for the crank
  • bolt circle diameter
  • distance between the bolts

as somebody that has never done it, I'd think this would be enough, yet I have found some in a shop where the compatibility is explicitly stated to my cranks, but also some where the measurements are the same, and my cranks are not in the list of compatible ones. Is the list just incomplete or inaccurate, or are there also different factors to pay attention to?

For now I will buy some where the compatibility is explicitly stated, but would like to know more in general.

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  • iirc BCD and distance between the bolts are directly linked to eachother so could be viewed as one paramater (BCD). – Maarten -Monica for president Feb 16 '20 at 10:07
  • here's an explanation on how to calculate one (eg BCD) when given the other (distance between bolts & number of bolts) wolftoothcomponents.com/pages/… – Maarten -Monica for president Feb 16 '20 at 10:08
  • if the distance between them is always the same, then sure. I don't know enough to know if there are cranks/chainrings with spacing that is not uniform. That's not so important, but thanks nonetheless – nomve Feb 16 '20 at 10:11
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    I've never had any issues replacing them just looking at bcd and number of bolts. some (older) chain rings are thicker which could have an impact on alignment (but if you adjust front derailleur after installing the new chaining there shouldn't be an issue generally. Other than potentially slightly different alignment i haven't personally experienced any other issues and I've replaced my fair share of chain rings (let's say 50 at least) on many different cranks. – Maarten -Monica for president Feb 16 '20 at 10:12
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    @Maarten-Monicaforpresident how about these, these, these ones and these. – Argenti Apparatus Feb 16 '20 at 12:07
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The FC-M430 Shimano Alivio crankset is very standard. The key spec's for determining chainring compatibility are:

  • BCD which you have: 104mm for outer & middle, 64mm for the small ring
  • Number of Bolts - 4

That said a few additional things which will affect shifting performance:

Ramps & Pins are designed into the chainrings so the crankset is a "system" and replacing the middle and large chainring with other brands/models may not shift quite as well.

Chainring thickness has varied slightly with the number of gears in the drivetrain and Shimano has expressed concerns in the past of the narrower 9 speed chain sliding off the middle chainring when downshifting. But lots of people have used 8 speed cranksets in 9 speed drivetrains.

And then there's the chainguard which bolts onto the outer chainring. Other brand or model chainrings may not have mounting holes for the chainguard.

Note that changing the number of teeth on the chainring can open up an additional set of issues with derailleur compatibility/adjustment and chain length.

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Unfortunately chainring compatibility can be a bit more complicated than number of bolts, BCD and pattern.

Higher end cranks such as Shimano Dura Ace or Ultegra have rings that are shaped to blend into the crank body. Those cranks are only compatible with the rings specifically made for them.

Some cranks may also require rings where the mounting points are offset laterally from the plane of the circle of teeth.

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  • Are you sure the chainrings themselves (on higher end models) are shaped to blend into the crank body? I thought that to get the 'transition' between chainring and crank body smooth they attached a piece of plastic. That's what I have on my tiagra crankset iirc. Could this also be the case for Ultegra and Dura ace? – Maarten -Monica for president Feb 16 '20 at 15:05
  • so is there a general guideline what to look for? does e.g. shimano mention it anywhere or it's basically hoping a shop will know? – nomve Feb 16 '20 at 16:11
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    @Maarten-Monicaforpresident: Ultegra and Dura-Ace are shaped in a way that they will only fit the specific cranks and there's no compatibility with lower end cranks either. – Carel Feb 17 '20 at 19:22
  • @Maarten-Monicaforpresident I believe that yes, the stock Shimano outer chainrings are shaped to blend into the crank arms. Some third party manufacturers (e.g. Specialties TA, Absolute Black) make outer chainrings for Shimano cranks but they don't blend them into the arms. Those two manufacturers do make covers that fit onto the chainring. Some pics of the covers at the link. elsewhere on the site, if you navigate to the chainrings and scroll through photos, you can see the crank without covers absoluteblack.cc/… – Weiwen Ng Feb 18 '20 at 20:56
  • Even lower-end cranks can be susceptible to non-fit despite carrying the same brand, BCD, and number of bolt holes. Especially the large outter ring. The shape and dimensions of the interior area--specifically any material inside the bolt holes can effect the fit--preventing the use of a new ring without modification. I bought from a co-op a large chainring still in package for a Shimano FC-M530 to use on my FC-M510. The new chainring had more material inside of the bolt holes and would not go on the 510's spider. – Jeff Feb 24 '20 at 14:44

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