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chainrings on a triple crankset

This topic contains 18 replies, has 8 voices, and was last updated by  JaySherman5000 5 mos.

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HiddenVariable

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Apr 8 2014 at 1:49pm #

afternoon, all!

i recently “upgraded” my front derailleur, not realizing that the minimum chainring teeth difference was a real thing i had to consider. as a result, i have a front derailleur that can only get the chain to the big ring if it is very poorly adjusted (i.e. i only have range of about 4 gears before trimming becomes an issue). so, my solution was to change the middle chainring.

now, i thought this would be a reasonably simple and inexpensive thing to do. apparently not so. kraynick’s was out of 39T rings, and the variety on the internets makes me very worried about the pitfalls of choosing the wrong one.

so, the question becomes: what do i need to consider? i intend to replace the middle 42T with a 39T. do i need a triple-middle-specific chainring? will it matter if i get one that is ramped and pinned differently from what i already have (pins, no ramps)? is it possible to perform this replacement without getting some crazy-expensive TA chainring?

tl;dr: how do i buy a middle chainring for a triple that is compatible with the rest of my drive train?


jonawebb

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Apr 8 2014 at 2:06pm #

You have to worry about the BCD number, so you can mount it. The ramps and pins are there to make the shifting work smoothly. I don’t think matching what you have is something you need to worry about. When I bought a TA Alize chainring to replace my Shimano middle the ramping was different from Shimano’s, of course, but it seemed to work fine.


Drewbacca

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Apr 8 2014 at 2:58pm #

You definitely want a triple specific middle. Personally, I’d try to get the middle and outer matched if possible. It shouldn’t be too hard to find a home for the outer ring you currently have.

What combination are you currently running? Which FD? What crank BCD?

You don’t need to go TA if you have a 130bcd or standard 110bcd crank… there are plenty of options out there. It gets more tricky if you are using a Campy crank from 2007 on.


Marko82

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Apr 8 2014 at 3:15pm #

the ramps and pins are there to make the shifting work smoothly

I have smooth/rampless small, middle and large rings on the bike right now and it works just fine with the exception that it takes a full crank revolution to fully shift sometimes. I use friction shifters and this hasnt been a problem in practice, but it can be a “feature” you may not want to have to get used to.


HiddenVariable

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Apr 8 2014 at 4:19pm #

the bcd is 130mm (5 bolt), and the derailleur is FD-6703.

so, something like this should work fine? i read some thread somewhere in which someone was trying to properly line up the chainrings, so that made me wonder if the ramps ought to have matched up with ramps on the other chainrings.

@Drewbacca, why do you say you’d match the other with it?

edited to add: another concern of mine is matching the cassette. i now have a ten-speed cassette, but the crankset was originally set up with an eight-speed. it hasn’t seemed to matter, but i wonder if adding a ten-speed-matched chainring to an eight-speed-matched crankset would be problematic.


Naomi

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Apr 8 2014 at 4:24pm #

I replaced all mine a few years back. This is what I remember…

Check the specs on your new FD. There’s a tooth-difference that works best between middle and large (it used to be 10, might have changed), and the gap from small to large is limited by the size of the cage. Small to middle also has a gap limit and if your small is very small then a third eye chain catcher helps, because it will keep the chain on the ring when changing down, which means you can then use more tension to get it to change up.

I changed from Shimano 32-42-52 to 24-38-48 which is much more Burgh friendly, and works fine with my original 9 spd FD. I bought TA rings from wiggle.com because I couldn’t find them anywhere else and only TA made the sizes I wanted (this might be different now).

There’s lots of useful advice on the Sheldon Brown site. http://sheldonbrown.com/front-derailers.html


Naomi

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Apr 8 2014 at 4:26pm #

By ‘keep the chain on the ring’ I meant ‘stop the chain from flying right over the top of the small chainring’.


Drewbacca

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Apr 8 2014 at 6:23pm #

HiddenVariable wrote:so, something like this should work fine? i read some thread somewhere in which someone was trying to properly line up the chainrings, so that made me wonder if the ramps ought to have matched up with ramps on the other chainrings.
@Drewbacca, why do you say you’d match the other with it?
edited to add: another concern of mine is matching the cassette. i now have a ten-speed cassette, but the crankset was originally set up with an eight-speed. it hasn’t seemed to matter, but i wonder if adding a ten-speed-matched chainring to an eight-speed-matched crankset would be problematic.

1. should work great and that price is incredible!
2. matched so that the ramps on the middle line up with the pins on the outer for optimal shifting… but, I trust Jon’s experience and it may not be necessary. I’d say that I don’t like to take chances, but then again, I’m running a Campy/Shimano mix so I guess I do like to live dangerously.
3. I wouldn’t worry about the cassette mismatch too much. The concern is that the chain is narrow enough to match the cassette (chain and cassette should always be matched imho) but not so narrow as to get stuck between chain-rings in the front. I don’t expect you’ll have a problem. If you did have a problem, it would be with the spacing between the rings more so than the width of the rings.


Drewbacca

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Apr 8 2014 at 6:38pm #

Naomi wrote:Check the specs on your new FD. There’s a tooth-difference that works best between middle and large (it used to be 10, might have changed), and the gap from small to large is limited by the size of the cage.

10 is Sheldon’s advice regarding a no-pin scenario. 12 seems to be the consensus where ramps/pins are involved. Oddly, Shimano has different numbers for their 105 and Ultegra of the same generation (see photo). The maximum difference can be taken with a grain of salt, as this is determined based on the worst possible chainline conditions (short chain stays and poor shifting technique i.e. cross-shifting).


HiddenVariable

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Apr 8 2014 at 10:31pm #

thanks, @Drewbacca. i am running a 10-speed chain, and i presume the actual chainring difference has to do with the lateral spacing of the ring itself, which should have minimal effect, but i guess i worry about the spacing between the rings. like, maybe the chainring is dished in one direction to an extent that it is closer to one side and farther from the other. but that is probably not a realistic concern.

as far as derailleur/crankset compatibility, sadly, it is a real thing. the reason the ultegra triple derailleur doesn’t match up with my perfectly reasonable (formerly standard, 52-42-30) chainring combination is because the derailleur cage itself is matched to the ultegra triple crankset gearing. that is, the inside of the cage extends downward to such a significant extent that if you try to use it with a 52-42 big-middle combination, once the inside of the cage pushes the chain out far enough that it will catch on the big ring, the inside of the cage is actually grinding on the middle ring. the only way to avoid that is to angle the cage so that you get awful trimming. or i guess use the appropriate combination of chainrings.


StuInMcCandless

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Apr 10 2014 at 11:58am #

I gotta admit, much of this is over my head. I thought with all the bike riding and hanging around bike folks for so long, I might have picked up enough technical info. Apparently not.

Rampless, pins, BCD numbers, short chain stays, trimming, dished chainrings, … *eyes lose focus*

So I can understand what’s going on, is there a particular Sheldon Brown thread or Park Tools video or some such, that can introduce the topic of derailleur specs?


jonawebb

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Apr 10 2014 at 12:05pm #

That reminds me. I have the FD-6603 I think and more than 10 T difference between my middle and outer chainrings. I like a wide range. Maybe the 6703 is different but I suspect that if you play around with it you can get it to work. Rotate it or something. Jerry will know what to do.
Hmm I see the max teeth difference for both derailleurs is 13T, which I guess you already know. So maybe you’ve already tried what I’m thinking of.


JaySherman5000

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Apr 10 2014 at 3:40pm #

@StuInMcCandless: I think this should be a helpful link.


Drewbacca

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Apr 10 2014 at 10:25pm #

Fortunately, the problem in question should only be applicable to triple specific derailleurs.

Here’s a basic lesson Stu, to get to the crux of the problem. I’m using a Campy FD for example but the visual is the same for Shimano.

Triple first followed by a double.


Drewbacca

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Apr 10 2014 at 10:44pm #

StuInMcCandless wrote:

Rampless, pins, BCD numbers, short chain stays, trimming, dished chainrings, … *eyes lose focus*

Ramps/pins are just for the sake of better shifting. Sheldon talks about the ramps in regards to cassettes. http://sheldonbrown.com/k7.html#hyperglide

Pins are just part of a combination which is used for chain rings. The pins catch the chain when you shift to a bigger ring. They are supposed to match up. From one company to another, they probably won’t match up. Even dealing strictly with Shimano, there is an “A type” and a “B type” (one for a 39t ring and one for a 42t ring in a double set up… I forget which is which, of hand, but they are supposed to be matched). A triple-specific middle chain ring will have pins to aid in shifting from small ring to middle. A double-specific ring of the same size will only have the ramps.

BCD is covered in depth by Sheldon. The short version is this: Campy is 135mm. Shimano is 130mm. The maximum small ring that can be used with Campy is 39t while it is 38t for Shimano. This is why “compact” cranks with a 110mm BCD exist, since you can go down to a 34t ring. A 74mm bcd is common for the small ring on a road-triple. So, you have some limitations on what will fit with a given crank. To spin you around even more, manufactures do other things to make sure that one 110mm bcd ring isn’t compatible with a competitor’s, such as misaligning one of the mounting points.

Trimming: I thought you were familiar with friction shifters? You should be all over that one.

Dishing? No idea what you are referring to in regards to chain rings. I think dishing is something you do to a spoked-wheel only? Chainrings have spacers and different offsets based on the width of the chain being used… I think that is what was meant by “dishing” but I’m not sure if the word is technically correct in relation to a chain ring.


abm760

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Apr 11 2014 at 10:32am #

HiddenVariable wrote:so, something like this should work fine? i read some thread somewhere in which someone was trying to properly line up the chainrings, so that made me wonder if the ramps ought to have matched up with ramps on the other chainrings.

You need to be careful with a middle ring like that one. I hope that it matches your crank. It looks like a ring that’s intended for a crank where the inner ring of the triple mounts to the middle ring. If your cranks are set up to mount the inner ring directly to the arms, you might end up with interference.

This is a ring from the same shop that does not have the provision for mounting the inner ring to the middle ring: 105 Middle Ring


JaySherman5000

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May 25 2014 at 6:42pm #

I’m topping this thread to document some mechanical happenings that are mostly related to the discussions here. I just re-geared my touring bike from a worn out 44-32-22 chainring set to a custom 48-34-22 (reusing the 22 bc it had seen very little use).

I was worried at first about things like tooth capacity, maximum tooth difference, pins & ramps, and whatnot. Everything I read recommended a 48-36-26, 46-34-24, or my original combo. For my own reasons, I wanted the gear range provided by 48-34 along with the “bail out” capability offered by the 22. So, after consulting the Gospel of Sheldon Brown, several internet bicycle forums, the High Septon, and my local Bike Whisperers, I decided to go through with the conversion. For those that care:

Front Derailer: Shimano Deore LX
Rear Derailer: SRAM X7 long cage
New Chainrings: 48t with pins & ramps>, 34t with neither pins nor ramps>
I also put on a new chain and cassette (10spd 11-32t) for good measure.

The install: changing out the chainrings meant I had to remove the cranks (had I known this would be required, I would have also changed the bottom bracket). After the new rings were on, I swapped the cassette on the back wheel, re-installed the cranks, and applied the new chain. To make it all work right, I had to loosen the front shifter cable, move the front derailer up a few centimeters, and then re-tune the shifter.

The end result: success! I was nervous about the large tooth difference between the front gears, but so far shifting has been buttery and nice. The last thing I think I need to do is replace the pulleys on the rear derailer, but otherwise everything went well. I hope this story will help others in their quest to build out their perfect bike. Ride safe!


Drewbacca

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May 25 2014 at 8:03pm #

Thanks for the update JayS5k!

I’m curious, when in the granny, how much clearance between the bottom of the chain and the top of the bottom-plate of the FD cage? I know it varies from one derailleur to another but I’d still like to know how much room to spare you have.


JaySherman5000

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May 25 2014 at 8:22pm #

@Drewbacca: I just re-checked it. If I have the bike cross-chained in the 22×11 combo (which no one should ever do) there is maybe 1/8″ or less clearance between the chain and the bottom plate on the front derailer cage. That distance increases as the chain moves up to larger cogs on the cassette, to a maximum of about 1/2″ or slightly more.

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