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Freewheel skipping the middle ring on upshifts

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Freewheel skipping the middle ring on upshifts

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Old 01-13-18, 10:29 AM
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Freewheel skipping the middle ring on upshifts

This isn't my bike, but it's sort of my problem. A triplizer customer of mine tells me that when he tries to shift from the small ring to the middle ring, the chain skips the middle ring and goes right to the big one. I don't have much detail at this point. The triplizer is a 144 bcd model, but I don't yet have any details on the tooth counts of the other two chainrings, freewheel cog tooth counts, etc.

Ideally I would be able to troubleshoot it directly, but he's 4000 miles from here. I'm hoping he'll send me some pictures soon.

I've seen this happen before, and in my limited experience it's usually caused by some mis-positioning of the front derailleur--usually because it's too high above the big ring, but sometimes because it's toed too far in or out at the front. I vaguely remember that toeing it in slightly at the front can improve things (that is, the problem occurs in the first place because the derailleur is toed outward in front), but I may have that backwards. I haven't run into this in years.

Also--and this is really interesting--the customer actually has two bikes and two triplizers, both of which have the same problem. Again, details of the two setups are scant at this point, but to me that suggests a setup error common to both bikes.

Help me out here! Does anyone have thoughts on this?
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Old 01-13-18, 10:42 AM
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I can see two possibilities. The first is, as you conjecture, the RD is too far from the rings. The second is that the cage is too flexible. The cage flexes as it pushed the chain sideways. When the chain finally lifts off the small ring the pressure on the cage goes away and it relaxes, meaning it pushes the chain even further. We had this problem on our tandem which made it throw the chain off in whichever direction it was shifting. A stiffer RD completely solved the problem.
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Old 01-13-18, 11:35 AM
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The cause I would expect would be that the difference in tooth count between the small and middle ring is as small or smaller than the difference in tooth count between the middle and big ring.

The chainring sizes have a huge impact on how robust of a shift that the rider can get while shifting up to the middle ring and down from the middle ring as well.

Shifting performance to and from the middle ring is best with half-step style triples, but short of that one should try to keep the difference in tooth count between the small and middle ring AT LEAST half of the total range/difference.

Note also that newer triple front derailers have "step" features formed into their inner cage plate which correspond to very specific tooth-count differences between the middle and big ring.
Violating the intended tooth count step can make for a failure to shift up to the middle ring with any authority at all.
Remember here that it's the big ring that sets the derailer's height, so the tooth count difference with modern front derailers references only from the big ring down to the middle ring.
This applies to both road and mountain triple derailers from roughly the last 20 years.

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Old 01-13-18, 11:41 AM
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When I installed a triple on my Raleigh, I spent roughly 1-1/2 hours getting it to shift correctly. It was very sensitive to the height of the FD (Campy NR) and it's alignment. I adjusted it so the FD sits a little higher that on my doubles and the cage is rotated so the rear sits slightly outboard of the front of the cage.
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Old 01-13-18, 11:58 AM
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Pretty hard to diagnose an issue like that at a distance, and with no details at all, but here's a checklist:

Is inner chainring on backwards? Sometimes people would flip these and the inner spacers would fit into the recesses meant for the chainring bolts, throwing off the spacing.

Front derailleur height? I recommend using the standard height from big chainring. "penny thick". Never had it not work. Check the basics. https://www.parktool.com/blog/repair...eur-adjustment

FD alignment? Generally outer cage should be parallel. Older FD will benefit from tweaking, and imperceptibly small inward cant. Can't explain that by text.

Chain length? IME the jockey cage vertical in biggest gear (shimano method) works better than the big/BIG +2 method for triples. Wrong chain length can really mess things up.

Try a different chain? Old stiff chain may be problem.

Lastly I'm guessing he's using vintage FD? As mentioned above, modern 'triple' FD are designed for specific chainring sizes and tooth counts, and are not flexible. Vintage FD work better for vintage style triples. CX-70 is a good modern derailleur for road triple.

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Old 01-13-18, 12:10 PM
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-----

If by chance chainsets in question are Verot it could be due to how the teeth are cut. Until 1977 all Verot chainwheel teeth were cut from one side of the stock only. Beginning in that year they changed to being cut from both sides of the stock. This makes for a difference in chainwheel spacing which can affect shifting. Sometimes cyclists fit late type chainwheels to early type arms or mix early and late type chainwheels in the same set.

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Old 01-13-18, 02:26 PM
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Originally Posted by dddd View Post
The cause I would expect would be that the difference in tooth count between the small and middle ring is as small or smaller than the difference in tooth count between the middle and big ring.

The chainring sizes have a huge impact on how robust of a shift that the rider can get while shifting up to the middle ring and down from the middle ring as well.

Shifting performance to and from the middle ring is best with half-step style triples, but short of that one should try to keep the difference in tooth count between the small and middle ring AT LEAST half of the total range/difference.

Note also that newer triple front derailers have "step" features formed into their inner cage plate which correspond to very specific tooth-count differences between the middle and big ring.
Violating the intended tooth count step can make for a failure to shift up to the middle ring with any authority at all.
Remember here that it's the big ring that sets the derailer's height, so the tooth count difference with modern front derailers references only from the big ring down to the middle ring.
This applies to both road and mountain triple derailers from roughly the last 20 years.
You're a sharp guy, dddd. I knew in a general way that too big a small ring could cause that problem, and I suspected that might be the case here, but I'd never heard it quantified the way you did above. The rule of thumb I'm going to tell people from now on is that the difference between small and middle should be two teeth larger than the difference between middle and large. The same difference in tooth counts can work, but two teeth larger is better.

Anyway, I heard back from my customer. His gearing combined a 55-42-34 in front with a 13-17-21-26-34 freewheel.

Back to the drawing board!

He seems like a good guy, and the two bikes in question are both beautiful Flying Scots--one from 1952, and the other from 1969. Live and learn.
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Old 01-13-18, 02:38 PM
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I suspect operator error when it comes to the shift lever.
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Old 01-13-18, 03:55 PM
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Originally Posted by jonwvara View Post
...His gearing combined a 55-42-34 in front with a 13-17-21-26-34 freewheel...

Thanks for the follow up.
With ring sizes like that, I would also expect that a downshift from the middle ring would be lazy at best, due to the increased span of chain from the point of contact on the outer cage plate to where the chain is being fed onto the teeth of the middle ring.


I prefer to use Shimano HG chain as my very best chance at getting difficult triples to shift correctly, and sometimes will even remove the ring and bend every third tooth of the chainring toward the NDS very slightly.
At times it's make or break!
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Old 01-13-18, 04:15 PM
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I concur with dddd. Small to middle tooth gap should be equal or greater than middle to big. A 45t middle would be better.

Even so, I suspect other issues are compounding the problem. I suggest double checking fundamental FD adjustment. I bet something else is off too.

FWIW, this is a good candidate for 1/2 step gearing. I've never really like 1/2 step myself, but with a wide ratio 5 speed freewheel, it may be the most sensible way to go for this particular triple set up. Is 55t outer really necessary?
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Old 01-13-18, 04:26 PM
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Originally Posted by Salamandrine View Post
I concur with dddd. Small to middle tooth gap should be equal or greater than middle to big. A 45t middle would be better.

Even so, I suspect other issues are compounding the problem. I suggest double checking fundamental FD adjustment. I bet something else is off too.

FWIW, this is a good candidate for 1/2 step gearing. I've never really like 1/2 step myself, but with a wide ratio 5 speed freewheel, it may be the most sensible way to go for this particular triple set up. Is 55t outer really necessary?
Well, it's a 144 Campagnolo double with a triplizer ring in the second position. There's no option for the middle ring other than 42 teeth, unless he gets a new crank. I suggested that he try a 52-42-30 with something like a 13-16-19-24-28 in back. That would approximate the wacky setup he had before (albeit with a few gear inches off the high) but with better performance and a more rational shift pattern
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Old 01-13-18, 05:17 PM
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His gearing combined a 55-42-34 in front with a 13-17-21-26-34 freewheel.
That's the craziest gearing combination I've ever heard of.
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Old 01-13-18, 07:36 PM
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Originally Posted by Kactus View Post
... and the cage is rotated so the rear sits slightly outboard of the front of the cage.
I believe this is the same thing @Salamandrine was saying. It isn't so hard to understand. Imagine viewing the crank from the DS. When the chain is on the small ring it runs through the cage lower, i.e. closer to the ground than when it is on a large ring. When you shift to a larger ring the chain not only moves outward, it also moves upward toward the top of the cage. If the cage is canted inward at the bottom, the chain moving upward is also pushed further outward by the upper part of the cage. You have to move the cage a certain amount to get it to rise off the small ring's teeth, but then the upper part of the cage forces it even further outward. Hence the overshift.

FWIW, our tandem has 52, 38, 26 rings, if I counted them properly. Maybe I miscounted and the small ring is 28. Anyway, it makes a very nice 1-1/2 step crossover with a 14-28 5-speed FW. The tooth count difference between small and medium rings is less than the difference between medium and large. In fact, if the two ratios between the pairs are about the same, a necessary requirement if the crossover is to be about the same between the pairs, then the tooth count difference must be smaller between the smaller pair. With a good FD, one of those new Simplex triple devices, it shifts flawlessly up and down. So I guess I would argue with dddd's requirement. I'd say instead that the ratio of medium to small should be equal to (or greater than) the ratio of large to medium. <line deleted - on further review the ruling on the filed is reversed>
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Old 01-13-18, 07:59 PM
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Originally Posted by jimmuller View Post
I believe this is the same thing @Salamandrine was saying.
He couldn't remember off hand which direction the front tilted so I checked mine to verify it. It was a very tricky adjustment to get mine shifting right. His friend does have some odd chainrings. I have 53-45-36 and am running a 13-28 freewheel.
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Old 01-13-18, 08:44 PM
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My head hurts.
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Old 01-14-18, 12:17 AM
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Originally Posted by jimmuller View Post
...So I guess I would argue with dddd's requirement. I'd say instead that the ratio of medium to small should be equal to (or greater than) the ratio of large to medium. Equal would be also the mathematical relationship that makes the tops of the three rings form a straight line so that the medium ring is not masked.

I stated: "The cause I would expect would be that the difference in tooth count between the small and middle ring is as small or smaller than the difference in tooth count between the middle and big ring." And I mentioned a possible derailer issue as well.


I simply stated what I expected the causes of the poor shifting to be.

There is no definite "requirement" per se, since many old Shimano Triple setups such as FC-M730 with no pickup pins and 28-38-48t chainrings shifts marvelously (under tremendous authority of the shift lever) using Shimano's period "UG Narrow" or newer HG chain.
And Shimano's newer offerings, even at the very lowest end of their lineup, likewise shift flawlessly using 24-32-42t rings!

But each step in the "wrong" direction (toward a relatively smaller middle ring) increases the requirements of chain and chainring design, and of a more suitable front derailer. For example, what works really well with HG chain may barely work at all with, say, Sedisport chain.

As I've said, sometimes I couldn't get my own selected parts to quite work well without going to the extreme or last-ditch route of removing the middle ring and bending every third tooth inward, as when I finally got an old 1970's Cyclone front derailer to properly index-shift via an Alivio shifter over a set of three selected rings (34, 42 and 52t iir) that I mounted to an old Miyata tourer's SR APEX 84bcd crank.

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Old 01-14-18, 12:31 AM
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Wow what a wacky setup. going to a 50 big ring would help a lot for reducing the gear overlaps.
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Old 01-14-18, 07:37 AM
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Originally Posted by dddd View Post
I stated: "The cause I would expect would be that the difference in tooth count between the small and middle ring is as small or smaller than the difference in tooth count between the middle and big ring." And I mentioned a possible derailer issue as well.

I simply stated what I expected the causes of the poor shifting to be.
Fair enough. What you did say was:

one should try to keep the difference in tooth count between the small and middle ring AT LEAST half of the total range/difference
Jon took this as a rule-of-thumb, and it's a decent one. My point was that it could be more restrictive than necessary. If I understand that quote correctly it says the middle ring should be at least "halfway" between the small and big ring. However an equal-ratio, i.e. constant cross-over setup would necessarily have the middle ring be smaller than that, and such setups can work well.

Some hypothetical numbers: A ring set of 52, 38, 28 has a ring-to-ring ratio of about 1.363 between each pair. With the right sprockets this would make a decent cross-over pattern. That the ratios between each pair of adjacent rings are the same means the cross-over pattern is the same between small-middle and middle-big. But the middle ring is only 10 teeth bigger than the small ring, 14 teeth smaller than the big ring. It is obviously less than halfway between the other rings. If you stick to that r.o.t. you could never have a setup like this.

Note, I deleted the last line from my previous note, a line you still have quoted. I, um, realized in a more sober moment that I had mis-thunk it. Or spoke before sufficiently thunking it. Or wrote before thunking it. Or something. I do that often enough I should know better.
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Old 01-14-18, 08:16 AM
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Originally Posted by jimmuller View Post
Fair enough. What you did say was:

Jon took this as a rule-of-thumb, and it's a decent one. My point was that it could be more restrictive than necessary. If I understand that quote correctly it says the middle ring should be at least "halfway" between the small and big ring. However an equal-ratio, i.e. constant cross-over setup would necessarily have the middle ring be smaller than that, and such setups can work well.

Some hypothetical numbers: A ring set of 52, 38, 28 has a ring-to-ring ratio of about 1.363 between each pair. With the right sprockets this would make a decent cross-over pattern. That the ratios between each pair of adjacent rings are the same means the cross-over pattern is the same between small-middle and middle-big. But the middle ring is only 10 teeth bigger than the small ring, 14 teeth smaller than the big ring. It is obviously less than halfway between the other rings. If you stick to that r.o.t. you could never have a setup like this.

Note, I deleted the last line from my previous note, a line you still have quoted. I, um, realized in a more sober moment that I had mis-thunk it. Or spoke before sufficiently thunking it. Or wrote before thunking it. Or something. I do that often enough I should know better.
Chiming in again here, what I like about my new rule of thumb--that the difference in tooth count between the small and middle ring should ideally be two teeth larger than the difference between the large and middle rings, although an equal difference is acceptable: It's always going to work (assuming that the derailleur setup, etc., is also correct).

That's not to say that other spacings can't also work. But my goal--as a guy who sells triplizer rings--is to keep people happy without getting into long-distance troubleshooting and explanations of what a gearing chart is. In fact, many people who buy triplizers are pretty conversant with spindle lengths and tapers, bottom bracket threading, thick cups vs. thin cups, bolt circle diameters, and all that stuff. In other words, many of them are bike nerds like those of us here. Quite a few of them are those of us here.

But quite a few are just people who own an old bike with desperately high gearing, and who just want to be able to ride it again. In other words, they're bike nerds in a very early stage of development. I want to keep things understandable for them, and not get into telling them how to very gently bend every third chainring tooth slightly outward (a good trick, dddd, but not one that I'd feel good about suggesting to a neophyte).

Once they have a setup that reliably works, they can figure out how to push the envelope on their own later on.

This is an interesting discussion. Thanks, everyone.
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Old 01-14-18, 10:10 AM
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Be sure to report back on the final verdict. Personally, I have my money on FD setup.

Oh, and agree that his gearing choices are very “unique.” He appears to have only gained one lower gear by installing a 34t. And he only has one higher gear when shifting from 42 to 55 - albeit a huge step of 31%!! That’s double what I prefer in the mountains. Good on you for suggesting alternate gearings, Jon. Other than pro racers, who regularly pushes a 114” gear anyway?? I consider myself reasonably fast and find 50x14 to be plenty big.
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Old 01-14-18, 11:15 AM
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My money is on FD set up also. Angle or height or both.

I seriously used to see reversed inner chainrings pretty often too when I was a repair guy. It's a very easy mistake to make. Double check spacing between all chainrings.

The bigger step from middle to big than small to middle thing is more something that works against you than a rule IMO. Main problem I see is the 55T big requiring the FD to be even further away from the small chainring than it would be normally. I recommend it be changed to 52t.
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Old 01-14-18, 11:25 AM
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Dumb question, but is he using a triple front derailleur? I assume he’s using a triple shifter as well, but if I learned anything from working tech support is that it’s worth (politely) asking if you don’t know 100% already.
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Old 01-14-18, 01:46 PM
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In the grand scheme of gearing, I don't see anyone out there worried about duplication of ratios or even half-stepping anymore.
With increased # of cogs, and even with just 5 cogs, it's more about having an easily-usable shifting sequence and ratio spread that hopefully can accommodate small 2-tooth cog size increments at least up to the 17t size.
So "crossover" chainring size differences that utilize a back-shift of the rear derailer to add one more ratio to the sequence is good, but can be conveniently skipped when lower-intensity riding in the city or downhill is encountered.


I like triples with a larger difference between the smaller rings for the added reason that at the lower speeds when the 1-2 or 2-1 shifts are used, 1) there is more gearing torque available to bridge a bigger % ratio step and still accelerate quickly, and 2) there tends to be a much bigger percentage of speed change during the time it takes to downshift, so that a bigger drop down to the small ring better maintains cadence in concert with the bike's speed.
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Old 01-14-18, 01:50 PM
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Originally Posted by tricky View Post
Dumb question, but is he using a triple front derailleur? I assume he’s using a triple shifter as well, but if I learned anything from working tech support is that it’s worth (politely) asking if you don’t know 100% already.
I don't actually know what he's using for a front derailleur. The rear is a Campagnolo Euclid, which I'd never heard of before and had to look up. Perhaps he is using a matching front?

In my experience, double derailleurs work about as well with triple cranks as triple-specific FDs do. The only issue is that a double derailleur is is more likely to rub when running slightly cross-chained gear combinations, and may have to be trimmed occasionally.
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Old 01-15-18, 10:31 AM
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Originally Posted by jonwvara View Post
In my experience, double derailleurs work about as well with triple cranks as triple-specific FDs do. The only issue is that a double derailleur is is more likely to rub when running slightly cross-chained gear combinations, and may have to be trimmed occasionally.
A bigger issue is that some double front derailleurs won't swing out far enough to fully reach the big ring enough to actually complete a shift. You can live with needing to trim when running cross-chained, but you really can't live with the chain not staying on the big ring.
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