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Short Cage on a Triple - Check My Derailleur Math

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Short Cage on a Triple - Check My Derailleur Math

Old 07-28-21, 04:40 PM
  #51  
ShannonM
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Originally Posted by 70sSanO View Post
With 7 speed cassettes, I would take them apart and space them like 8 speed. It doesn't impact the front derailleur, but it lets you run 8 speed shifters. It also helps, a tiny bit with front derailleur trim.
Do you notice much of difference vs. using the cassette as-is?

I've always mixed and matched 7 and 8 speed Shimano parts based on what was on hand, and always had good, reliable indexing every time. Even 7-speed Deore XT thumbshifters on an 8-speed cluster with a 9-speed XTR derailleur shifted great. (That one was a bit tiddly to set up the first time, but once it was dialed I never had to mess with it.)

--Shannon
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Old 07-28-21, 05:06 PM
  #52  
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Unfortunately I have enough OCD with shifting precision that I’m not a good one to answer that.

I’ve never run 8 speed shifters with 7 speed cassette as is. The 9 speed RD is of no consequence as more of our bikes have 9 speed RD’s and not 9 speed cassettes or shifters.

Even when running 7401 shifters, I spaced the 7 speed cassette at 3.08mm as it seemed better with the alternate cable routing.

John
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Old 07-29-21, 12:18 PM
  #53  
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Check this out: https://web.stanford.edu/~dru/triplecheat.html.

I'm not suggesting that fellow is an authority but:

1) He represents one data point.

2) He's obviously given this some thought.

3) He is concerned about the big-big combo. The quote below is from his web page.

Originally Posted by webguy
Are there any disadvantages? Sure, you can jam the chain severely if you use the big-big combo and your derailleur can't handle the chain tension, causing all sorts of potential problems, like bent dropouts, damaged derailleurs, broken chains, etc. Using the small-small combo leaves plenty of slack in the chain, which can now freely slam into your chainstay, removing paint and gouging it.
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Old 07-29-21, 02:33 PM
  #54  
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Originally Posted by Harold74 View Post
Check this out: https://web.stanford.edu/~dru/triplecheat.html.

I'm not suggesting that fellow is an authority but:

1) He represents one data point.

2) He's obviously given this some thought.

3) He is concerned about the big-big combo. The quote below is from his web page.
What he says in the quote is generally understood to be correct. You won't find much disagreement.
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Old 07-29-21, 03:15 PM
  #55  
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Originally Posted by shelbyfv View Post
What he says in the quote is generally understood to be correct. You won't find much disagreement.
I guess I just wish that somebody could explain the nature of the problem in a way that spoke to me. A 105 SS is rated for a.30T max cog. I'm running a 28T. What else matters for big-big if the chain length is sized for big-big with a plumb derailleur arm?
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Old 07-29-21, 03:28 PM
  #56  
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"and your derailleur can't handle the chain tension," implies that the chain is too short. That's all he's saying. I don't see that it has any bearing on your issue, whatever it is.
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Old 07-29-21, 04:51 PM
  #57  
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Originally Posted by shelbyfv View Post
"and your derailleur can't handle the chain tension," implies that the chain is too short. That's all he's saying. I don't see that it has any bearing on your issue, whatever it is.
So what you're saying then is that the web guy's statement is generally understood to be correct even though his implied assertion that it was a function of undersized derailleur capacity is incorrect? And that, because his big-big problems were merely a function of his failing to size his chain correctly?

If you are in any doubt as to what my "issue" is here, refer back to the thread title. My issue was the now largely answered question of whether not my derailleur math was correct with respect to determining the smallest cog size that could be used when a short cage derailleur is combined with a triple crankset.
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Old 07-29-21, 05:34 PM
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Glad you have it resolved.
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Old 07-29-21, 09:40 PM
  #59  
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Originally Posted by Harold74 View Post
So what you're saying then is that the web guy's statement is generally understood to be correct even though his implied assertion that it was a function of undersized derailleur capacity is incorrect? And that, because his big-big problems were merely a function of his failing to size his chain correctly?
It's not a matter of sizing the chain "correctly", it's a matter of how you choose to size it when no sizing is correct. If you err short, the problem is that it goes taught toward the big-big; if you err long, the problem is that it goes slack toward the small-small. If you stay in the middle, you can get some of both problems.

Last edited by HTupolev; 07-29-21 at 09:48 PM.
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Old 07-30-21, 04:22 AM
  #60  
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This thread is becoming a Bikeforums classic.
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Old 07-30-21, 05:23 AM
  #61  
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Originally Posted by Harold74 View Post
Check this out: https://web.stanford.edu/~dru/triplecheat.html.

I'm not suggesting that fellow is an authority but:

1) He represents one data point.

2) He's obviously given this some thought.

3) He is concerned about the big-big combo. The quote below is from his web page.
One more thing:

4) He is a fool to size the chain that way.

Last edited by Kapusta; 07-30-21 at 05:37 AM.
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Old 07-30-21, 08:46 AM
  #62  
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Originally Posted by HTupolev View Post
It's not a matter of sizing the chain "correctly", it's a matter of how you choose to size it when no sizing is correct. If you err short, the problem is that it goes taught toward the big-big; if you err long, the problem is that it goes slack toward the small-small. If you stay in the middle, you can get some of both problems.
Like Goldilocks, I plan to size it "just right" for the big-big combination and to do that no differently than I would if I were using a derailleur sized for the appropriate capacity. The 105 short can handle 30T in the back and I'm only running 28T. In my mind, this means that:

1) If the chain winds up to short for big-big, that would have happened even with a normally sized derailleur and would just be function good, old fashioned screwing it up. It would have nothing to do with the unconventional derailleur choice;

2) There's really no such thing as a small-small problem since I don't plan to use all of the gears. Once everything's set up, I'll put the bike in the repair stand and run through the cassette to verify that the gears that I calculate should still work without excess chain slack in fact do still work without excess chain slack. Then, forever after, I'll probably use two gears less than that.
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Old 07-30-21, 09:43 AM
  #63  
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Originally Posted by Kapusta View Post
One more thing: 4) He is a fool to size the chain that way.
I contacted Drew. He's a good guy and a gentlemen. That said, it's something of a relief to know that I'm not alone in questioning his chain sizing strategy. Drew sold the bike that he set up this way long ago and as a result, isn't actively interested in the topic any longer I don't think. He gets high marks for putting forth the effort of creating that web page on the subject in my opinion though.
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Old 07-30-21, 09:49 AM
  #64  
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Originally Posted by grizzly59 View Post
This thread is becoming a Bikeforums classic.
I'm curious, what makes you say that?

I've been a heavy contributor and forum moderator for over 20 yrs over in structural engineer land. That said, I'm new to this forum and this is only the second forum that I've ever participated in. I get the sense that things are a bit different here compared to what I'm used. to. In my engineering forum, a good thread might go 20-50 posts and I've been involved in a few that exceeded 300. I've certainly read a few lengthy ones here too (countersteering physics comes to mind)..
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Old 07-30-21, 09:59 AM
  #65  
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Following the advice of the mid-90’s Stanford blog is predicated on one thing, you know exactly what gear you are in with a split second glance or by feel of the shifter position. Your success will depend on employing the same/similar setup.

The author is basing his decision on a 3x8 with bar end shifters. It does not take a mental giant to know what cog is being used with that setup, or even downtube shifting, to avoid the big-big and not rip a rear derailleur apart. Although even the best laid plans…

It is an interesting dilemma with fatigue/heat that stroke you mentioned. You might want to go with a bar end setup so you are not removing your hand from the handlebar. STI’s are the safest shifting system, but there is no way you can look back at the cassette before having to react quickly.

My advice is to go for it and bring a compact chain breaker and a couple of quicklinks; and maybe a spoke wrench. If it doesn’t work, worse case is hoofing it back home or the trailhead. Best case is riding back as a single speed.

John
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Old 07-30-21, 10:13 AM
  #66  
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Originally Posted by Harold74 View Post
I contacted Drew. He's a good guy and a gentlemen. That said, it's something of a relief to know that I'm not alone in questioning his chain sizing strategy. Drew sold the bike that he set up this way long ago and as a result, isn't actively interested in the topic any longer I don't think. He gets high marks for putting forth the effort of creating that web page on the subject in my opinion though.
He sold the bike setup short-chained for big-big? I sure hope the buyer fully understood the implications of that.

You are generous. I do not give high marks for putting terrible ideas out on the internet.
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Old 07-30-21, 10:31 AM
  #67  
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Originally Posted by Harold74 View Post
I contacted Drew. He's a good guy and a gentlemen. That said, it's something of a relief to know that I'm not alone in questioning his chain sizing strategy. Drew sold the bike that he set up this way long ago and as a result, isn't actively interested in the topic any longer I don't think. He gets high marks for putting forth the effort of creating that web page on the subject in my opinion though.
I doesn’t surprise me. Things change. Time moves on. I know from my own exercises that a good deal of the fun is succeeding and making something work that others dismiss. That is the end goal as it will never really surpass the latest technology.

In some cases those exercises stick and in others, I just move on; even if it was successful. Proving something works and employing it long term are two entirely different things.

John
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Old 07-30-21, 10:45 AM
  #68  
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Originally Posted by Harold74 View Post
I'm curious, what makes you say that?

I've been a heavy contributor and forum moderator for over 20 yrs over in structural engineer land. That said, I'm new to this forum and this is only the second forum that I've ever participated in. I get the sense that things are a bit different here compared to what I'm used. to. In my engineering forum, a good thread might go 20-50 posts and I've been involved in a few that exceeded 300. I've certainly read a few lengthy ones here too (countersteering physics comes to mind)..
A thread doesn't have to be lengthy to become a classic, it can have other attributes. Here's another "new to derailleurs" thread that most found memorable Shimano derailleur design flaw.
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Old 07-30-21, 10:56 AM
  #69  
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Originally Posted by 70sSanO View Post
You might want to go with a bar end setup so you are not removing your hand from the handlebar.
That advice I can certainly follow. I'm a bar end shifting fanatic and the bike is set up as bar end shifted 3 x7. I agree, I do maintain a pretty good awareness of where I'm at in the back with that setup. In the front, I'm torn as to whether friction or STI would be safest. Things I've considered:

1) The heat stroke argument where I just shift down from the big ring to the middle ring with excessive zeal.

2) With STI, I'd mostly have to actively choose to hit the lever to go down to granny.

3) With STI, if the tuning was poor or I screwed up a trim adjustment, maybe I could windup at granny by accident?

As others have said, I'm looking as some risk with this setup no matter how I slice it.

With regard to risk, one factor that I hope bode well for me is this:

A) This time last year, I'd not done so much as swapped out a bike chain. Now I've done a couple of complete tear down & rebuilds with a bunch of other projects on the go.

B) In the past, bicycle maintenance for me basically meant riding until horrible noises cropped up and then riding for another season before visiting the LBS. Now I do a rudimentary inspection on my bikes before most rides and adjust the drivetrain regularly on my own.

It's impossible to quantify the difference but, even with my non-conventional derailleur setup, I feel than I'm riding safer now than I was a year ago. Ditto for my family whose bikes I now maintain.
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Old 07-30-21, 05:09 PM
  #70  
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Big Big is simple: Size your chain so that you can run Big Big, even though you never plan too. Otherwise, if you shift into that combo (even if you don't ever plan to, Murphy's law applies) combo, crash is likely (chain and pedal just stop moving, in my case wheel stopped also) how much it hurts is the speed you are going

I think the best solution to OP's need is simple, is the most classic, is a virtual bike law and has not been mentioned yet N+1...... add a bike for hauling the dog trailer around.

FWIW over time I have moved to small small chain sizing but don't think it will fork for OP unless he goes to derailer that can handle the entire range.
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Old 08-01-21, 02:20 PM
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Originally Posted by shelbyfv View Post
A thread doesn't have to be lengthy to become a classic, it can have other attributes. Here's another "new to derailleurs" thread that most found memorable Shimano derailleur design flaw.
I hope you are not comparing the OP from this thread to the OP of that one
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Old 08-01-21, 04:09 PM
  #72  
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Originally Posted by squirtdad View Post
Big Big is simple: Size your chain so that you can run Big Big, even though you never plan too. Otherwise, if you shift into that combo (even if you don't ever plan to, Murphy's law applies) combo, crash is likely (chain and pedal just stop moving, in my case wheel stopped also) how much it hurts is the speed you are going

I think the best solution to OP's need is simple, is the most classic, is a virtual bike law and has not been mentioned yet N+1...... add a bike for hauling the dog trailer around.

FWIW over time I have moved to small small chain sizing but don't think it will fork for OP unless he goes to derailer that can handle the entire range. https://www.youtube.com/watch?v=QuhHn7HaZcQ
The last time I left my bike in a bicycle shop to have some work done on it was a number of years ago. Due to events after that I now do all of the mechanical work on my bikes.

What happened was the mechanic put too short a chain on the bicycle and never informed me of that. I was getting ready to cross a busy highway and shifted into a lower gear forgetting that I was in the big chainring. It turned out that the lower gear was the largest rear sprocket. When i went to pedal the entire drivetrain locked up and I tipped over to the right. Fortunately there were no cars or transport trucks coming at the time. Accidently shifting into a big big combo can have nasty consequences.

Also, if a chain is too slack in the small small combo, I think there's a risk of pulling the derailleur around and up into the sprockets which will also lead to unpleasant things happening.

When I run a triple crankset I use a proper triple capacity rear derailleur.

Cheers
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Old 08-03-21, 10:41 AM
  #73  
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Update: I took this bike for a four hour ride on Sunday where two interesting things happened.

1) I did in fact accidentally shift across the middle chainring and into the granny ring once, dropping the chain in the process. And that was with the original, properly sized derailleur.

2) At the end of the ride, I got lost and wound up doing a bunch of unplanned, urban riding while very tired. For that, because it was stop and go and I was rarely getting up to speed, it was an asset to be able to use most of the rear cassette from the granny gear.

So those things, along with comments here, have me re-evaluating things.
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Old 08-03-21, 11:02 AM
  #74  
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Yesterday I put the drive drain on the 1986 Miyata 210 refurbishment that I'm doing for my wife. See the photos below, and the captions, for how this triple is set up. I used one of the methods from my Zinn book whereby I size the chain for big-big plus one chain link (1" - 1.5" extra). Do we feel that I've hit the optimal chain length here? Or should I try and squeeze another link out of big-big? Small-small runs but:

1) The chain is pretty slack.

2) The chain almost rubs against itself at the low jockey will at the return intake.

3) The chain is in danger of bouncing against the front derailleur cage.

My suspicion is that this is about as good as this will get for the original equipment on this bike and that, back in 1986, the expectation was that you just stayed the heck out of the small-small gear combo.

Per this discussion, I'm currently more fearful of a big-big catastrophe than I am a small-small catastrophe.

Would y'all pull another link out of the chain? It's missing link so that's easily doable. And, on big-big, it seems that the whole derailleur would just swing around a bit more CCW around the direct mount bolt.


Big front, big back.

Small front, big back.

Small front, small back.

Small front, small back, FD view.
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Old 08-03-21, 12:19 PM
  #75  
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Looks about right to me.

If you remove a pair of links, the chain will very likely be too short for the big-big combination, which would be dangerous. While that is an inefficient gear for riding, it can happen inadvertently.

Looking at your other thread regarding FD cable routing, it appears that the front derailleur could be lowered several millimeters, so that it just clears the big ring. That will improve front shifts and decrease the likelihood of throwing the chain.

Regarding throwing the chain when shifting to the granny ring, I use chain catcher to prevent that possibility.

https://www.universalcycles.com/shop...16&category=54

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