Ultegra chainrings: BCDs and versions

munkster
munkster Posts: 819
edited January 2019 in Workshop
Does anyone know how Ultegra 6800 and 8000 chainrings compare? Are they the same things (they look similar) or is there something whizzier about the 8000 ones?

Also, did I read that they all have the same BCD now or is that just the 8000s?

Thanks!

Comments

  • akh
    akh Posts: 206
    Both have a 110mm BCD with the same bolt positions. Aftermarket rings can be made to fit both, but shimano changed the shape of one arm of the spider for R8000, so newer rings are probably backwards compatible, but older rings designed for 6800 are unlikely to fit R8000. Go to 3:56 in the below video and you'll see what I mean.

    Basically, they extend one arm of the spider out a little bit. This will prevent an older ring without the cut out mounting, but a new ring with the cut out should probably mate to the old style.

    https://youtu.be/RmJm8nemLAs

    In terms of the actual performance, shift quality, etc, no idea.
  • munkster
    munkster Posts: 819
    Ah, that''s very useful thanks. Maybe I'll just stick to the 6800 stuff then. Finding the right 6800 chainset (right crank arm length combined with right rings) on the 'bay is proving a bit of needle in a haystack so was looking to maybe cannibalise two and make one chainset that suits me!!

    Out of interest I don't suppose you know whether 6800 chainrings are the same as 5800 (105) chainrings? For the extra money I presume there is *something* special-er about Ultegra?
  • timothyw
    timothyw Posts: 2,482
    The difference is that the ultegra chainrings are lighter and easier to clean - they have a sandwich construction so the backside of them is smooth, whereas if you find a picture of 5800 chainrings they have a bumpy back with what appear to be milled out sections, and have a reputation for collecting dirt there although that could just be speculation.

    In practice they look very similar (from the side) and will be very similar in performance.
  • munkster
    munkster Posts: 819
    Yep, I've got 105 5800 on another bike and that description is correct, I just have no experience of Ultegra but that sounds about right! Thanks again.
  • akh
    akh Posts: 206
    TimothyW wrote:
    The difference is that the ultegra chainrings are lighter and easier to clean - they have a sandwich construction so the backside of them is smooth, whereas if you find a picture of 5800 chainrings they have a bumpy back with what appear to be milled out sections, and have a reputation for collecting dirt there although that could just be speculation.

    In practice they look very similar (from the side) and will be very similar in performance.

    I have 105 on my bike. I can't say that mud or dirt has collected in the back of the chainrings, but then I don't really ride in muddy or very wet conditions, and I have full mudguards. If it did collect and crud, I can't see it causing any mechanical problems for the bike. Although the chainrings might have different construction and quality, I'm pretty sure they have exactly the same dimensions of the mating parts, as all aftermarket rings I've seen advertise as being compatible with all same generations cranks, e.g. 4700, 5800, 6800, and 9000.

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