5

I have search the internet but to no avail to try and find a 74mm bcd 28t or 26t inner chainring with 4 bolts.

Does such a thing exist?

The nearest I can find it this but I want less than 30t:

http://picclick.co.uk/SHIMANO-FC4703-TIAGRA-10-SPEED-74mm-BCD-4-262545355186.html enter image description here

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  • 1
    A 74 mm bcd constrains you to a minimum of 24 teeth, so it should be theoretically possible (but maybe not financially feasible -- the audience is essentially just new Shimano triple owners). The other option is to switch the crank to a 5 bolt where such rings are easy to find. – Batman Aug 27 '16 at 14:56
  • Ok where do I find the 4 bolt 74mm chainring? – Jim77 Aug 27 '16 at 19:04
4

I've scoured some distributors and I don't think this exists. There's really only a couple 4-bolt asymmetrical triples out there period, and they haven't been out very long. I don't think you're going to see this anytime soon either, because it would blow past the RD max capacity specs of the applicable groups, which is a non-starter from a manufacturer's perspective. Sadly, these are not the cranks to own if you want freedom to customize your gearing, which is pretty ironic since conventional 110/74 are some of the best of all time for it.

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  • Thanks for confirming Nathan. So looks like I need get a 5 bolt triple for the front. Would it be best to go down the tiagra 5 arm route? Would previous models be compatible with my tiagra front mech etc? – Jim77 Aug 28 '16 at 6:58
  • It depends on what gearing you want, but if the 39 and 50 are staying then any of the 5-bolt 30/39/50 10-speed Shimano triples would be fine. Of note is that you're bypassing Shimano's total capacity spec to do this, and there's several caveats. First is the FD may not physically be able to reach down that far. Usually this isn't the limiting factor but I haven't done it with FD-4703 yet. Second is you'll be limited on what small/small combinations you can use without cage rub. Third is that shifting performance can be marginal, and you may need to add a chain catcher to prevent chain drop. – Nathan Knutson Aug 28 '16 at 16:15
  • Thanks Nathan. What do you mean by "shifting performance can be marginal"? What is a chain catcher. How will I know if I need one? – Jim77 Aug 28 '16 at 16:55
  • STI/front indexing in general, and for road triples in particular, are pretty reliant on their ramping, FD cage profiling, and tooth profiling all working in unison for shifting to be as smooth and consistent as intended. It tends to still be workable, but the results are a little unpredictable. A chain catcher is a plastic piece that clamps to your seat tube that prevents the chain from being able to fall off the inner ring. They let the inner limit be a bit further out, which can be useful here. I put them on preemptively when doing this, but you need it if your chain is dropping. – Nathan Knutson Aug 28 '16 at 17:26
  • Thanks Nathan. So would you advise I go down the Tiagra 5 bolt route then bearing in mind the shifting issues? I hope to put a 26t on. – Jim77 Aug 28 '16 at 19:30

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