I had an FSA Vero triple chainset (30,39,50...paired with a Sora 9-speed transmission) and replaced the middle chainring with a 42 tooth ring. Now I sometimes get the chain not going all the way to the small ring when down-shifting. It works a lot of the time, bit sometimes, under load, it will rest between the rings and they will spin without engaging the chain. It doesn't jam, not enough room.

I'm thinking 2 possibilities:

1. New middle ring is incompatible (it had indents for the bolts, and upshifts fine, so don't think its on backwards.) It is labeled as a 10-speed ring.

2. Small ring got put back on backwards. When looking at it, the dish of the teeth take them father away from the middle ring. Is that correct? Flipping it would definitely bring them closer, bit if its wrong might make them too close...there are no markings on the small ring, or indents for bolts to inset...very plain.

Any help would be appreciated... Otherwise ill try flipping the small ring and see what happens.

With friction shifting I never had this issue.. 52-42-26 .. 50-40-24.. 48-36-22..

.Too vague.. measure it.. speak of those numbers...

Maybe will try tonight...what I mean is that the teeth of the ring are closer to the center of the bike than the center of the ring. So flipping it will definitely make them closer...bit maybe too close.

Chain line; a 2nd line parallel to the bike center line ..... distance to the middle chainring ,


and the cog in the middle of the rear cluster, 5-7-9-11, or the gap between the 2 central cogs , if an even number 6-8-10.





....

Yes, it could be backward, or a spacer misplaced? Wouldn't hurt to take it off and check. Does the middle ring have any ramping to it?

Yes it does, and as I said, it upshifts small to middle. The ramps may be too far from the center of the ring?

This is it, the 42t one...
https://www.amazon.com/gp/aw/d/B007HVFPU0/ref=mp_s_a_1_1?ie=UTF8&qid=1515004488&sr=8-1&pi=AC_SX236_SY340_QL65&keywords=fsa%2B42%2Btooth%2Bring&dpPl=1&dpID=41%2Bfgh96glL&ref=plSrch&th=1& psc=1

12strings, If up and down shifting between middle and outer is okay, flip the inner chain ring and see ho w that works.

Brad

Normally any markings like tooth count are stamped on the side of the inner ring that faces the frame.

I've seen this happen, even with friction shifting, when using a modern narrow chain with a crank designed for a wider chain.

A couple things to try: 1) as you suggest, perhaps the middle ring is backwards, although the counterbores for the chainring bolts make this difficult to miss. It would be an easy fix, if it is the case, though.


2) Try a wider chain. Are you perhaps using a 10 or 11-speed chain with your 9-speed cluster?

I am definitely using a 9-speed chain. Upon further examination and experimentation, I have determined that the inner ring WAS oriented correctly...flipping it made the chain rub the middle ring constantly.

I also determined that the new chainring does not seem to have as large of ramps as the old one, so that seems to be the problem. I plan to install the old ring...back to 39t.

Any pics of the setup as you had it? Since you're mixing chainrings that weren't designed to shift together, you might try re-orienting the middle ring in one of the other 4 possible positions to see if it shifts better for you.

Thanks, I think I'm done experimenting with this ring. The ramps are noticeably smaller on the new ring, and they just don't stick out enough to consistent push the chain onto the small ring.

No big loss, it was a $20 chainring. I was hoping to get a bit more top end out of my middle gear, but its not a big deal.

Fyi, I think I got mixed up in my mind, having read that a 10 speed crankset will work with a 9 speed drivetrain...I mistakingly assumed that a 10-speed chainring mounted on an "8/9" (per the labal on my fsa crank) crank would also work, but it seems the spacing of the rings is too wide to work consistent.

What probably WOULD have worked, is putting the small ring on backwards, with some kind of spacer to move it a bit farther from the middle ring, bit not as far as it was when installed correctly.

I prefer a 42T to a 39T as well. Gives you a little more upper range before you need to switch out of it, so I get it.

Potentially you can fill the gap with spacers and an extra set of bolts , DIY drilled and threaded..

so the chainrings wont spread, and the chain wont force itself in the gap.



You create unnecessary problems trying to shift under a load, are you doing that ?








...

It is possible that your problem is related more to 1) your Sora FD (which I am going to assume is being shifted by an STI and not a down tube or bar end friction shifter), and 2) the change in chainring size. I know that Shimano STI shifting systems tend to be very sensitive with regard to chainring tooth count, and even though 39 to 42 teeth doesn't sound like a lot, it may be just enough to confuse your FD.

I experienced this personally when trying to improve the shifting on my Voyageur: it balked badly between the middle and inner gears as a 50/34/24 and after trying multiple FD's would only make the shift if I was four gears down from the largest cog, but it now shifts perfectly every time in every possible gear combination using a crankset with the 48/36/24 chainrings for which it was designed. So, there's that.

There's also difference in chainring ramps and gaps profiles. 42-52 combo doesn't use the same profile as 39-53 one. The old standards of Shimano chainring labeling were A and B. Now they have also M (for MTB I guess), T for trecking, FD, NB and loads of others. Combining two (or three) different labels on one crankset is not advised - sometimes it works better, sometimes worse. Some explanation can be found here (A, B and E types at least):

The Truth About the Shimano A and B Type Chainrings - The Tall Cyclist

An excellent point, and one which I competely missed. That happens when you exclusively use downtube shifters- everything can eventually be made to work!

Well, the original crank, chainrings and the new one were FSA.

With Sora derailer. I'm sure there is a shim fix possible, but not sure I want to mess with it.