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I have a road-biased hybrid that came with a compact 110mm BCD 50/34 Shimano Sora crankset and chainrings. I'd like to upgrade the inner ring to 39, but I'm having some trouble figuring out what to buy.

I initially picked up a Vuelta 39T "flat" model, but I can't get a clean shift from 50 to 39; the chain slides into the space between the rings, then floats on top of the cogs in the bottom ring, before finally meshing. This occurs when I'm at around 20T or smaller in the rear, regardless of how I've adjusted the front derailleur. The stock 34T Shimano chainring seats immediately. Somehow the Vuelta cogs never seem to line up properly when the chain comes down.

Do I need to replace both chainrings? Or do I need a Shimano model of the 39T? If so, from what generation (e.g., would a from chainring designed for an 11-speed chain still work with this 9-speed Sora?)? Shimano's compatibility chart seems not terribly helpful for this one. My current plan is to upgrade the whole crankset to a 105 5800, but I'd rather not if I don't have to.

  • upgrade the inner ring to 39 A few years late here, but there's no reason to do that. All that does is make your lowest gears bigger/harder to pedal at the cost of adding a lot of overlapping gears. You can do the same thing just by replacing your cassette, going from something like an 11-32 to an 11-28, or from an 11-28 to an 11-25 or 11-23. Changing the cassette like that also reduces the gap between gears. – Andrew Henle Apr 9 at 19:44
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Take a look here http://www.vueltausa.com/components/chainrings.html It looks like the flat series is for single speed or old style 5 or 6 speed non indexed shifting bikes.

Suggest you need the SE Plus range http://www.vueltausa.com/components/chainrings/se-plus-chainrings.html which is designed for 7 to 9 speed. It should be narrower than what you have, which may be why the chain is fouling.

  • Good point, thank you. Unfortunately, it appears they only have 36T in that design. It's surprisingly hard to find 39T in 110mm with a 5-bolt design. If I opted for the 5800 crankset, do you know if I'd have to replace any other parts? – Alex Jul 7 '15 at 2:37
  • I guess it's not common as most road chain sets will already be 52/39 and riders after looking for easier gearing alternatives. If you going to 105 level, you are jumping to steps up from Sora, so your chainset is a higher spec than the cassette and chain. Maybe a Tiagra chain set would suit? – Kim Ryan Jul 7 '15 at 6:29
  • Specialites TA makes 110mm 39 tooth chainrings that are easily available from European mail order. – ojs Jul 8 '15 at 15:22
  • The more I learn about cranksets, the more I'm realizing the importance of matching the chainrings. I may have to replace the 50T ring also. The only reason I haven't opted for Tiagra is for aesthetics; I'd like to keep the rings and pedals black if possible. The TA rings mentioned above appear to cost as much as the 105 set in entirety. – Alex Jul 9 '15 at 0:46

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