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Optimal Chain Length for 1x

Old 12-15-16, 09:11 PM
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Optimal Chain Length for 1x

Hello
I'm familiar with sizing chains for usual 3x/2x drivetrains; wrapping big+big+1 method to determine minimal length, and the derailer pulley contact check to determine maximum length. typically ending up with not much margin between these and going minimal length.

However, I'm relatively new to 1x drivetrains, and they bring up the question of ideal chain length for shifting performance.
being a 1x, the margin on derailer capacity is huge. a very big difference between minimum and maximum chain length allowable.

so how do I decide? especially given that the chain length will end up affecting derailer body position; which in turn will affect shifting performance -but exactly what effects I am unsure of

shorter chain rotates the cage forward, longer lets it sit further back... which way is better for shifting responsiveness? and this is clearly a much bigger factor than what a b-tension screw will be able to account for alone
perhaps there's an ideal angle for the cage to sit at?
what say the experts?
Thanks
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Old 12-15-16, 10:37 PM
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So a lot of shifting performance is dependent on the gap between the guide pulley and the cog set's underside. If the der cage has it's pivot on axis with the pulley then as the cage plays in and out the pulley won't change WRT the cog underside (as when the front is shifted). If the cage has it's pivot off center from the pulley's then as the cage plays out chain (as when shifting from a small ring to a larger one up front) the "open chain gap" will increase. this increase means more link pivots will need to slop over to their limit before the chain gets moved to the adjacent cog in back (when next shifting there).


So the question is which der cage design do you have? In an ideal rear shifting world the guide pulley will sit a handful of MMs below every rear cog regardless of what's going on with the ring(s). The cassette's cog growth (the range), the B screw setting, the der cahe pivot design, the chain length (with off set cage/pulley pivots), the hanger geometry all come into play.


When I set up a drive train I usually initially cut the chain to the longest that will work without the cage/chain "over wrapping" when the smallest ring/cog combo (unless the gear range is exceeding the der's specs). Then I might shorten the chain one link (pair) at a time if the shifting is less then ideal IMO and IME. Andy.
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Old 12-16-16, 02:37 AM
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It's a deore-m592
I'm new to this modern-er design

good point, the upper pulley is co-axial with the cage pivot
i suppose that means, chain length is going to have minimal effect?

Also to my confusion, I see that the B-tension, is not a tension adjustment at all, as there is no upper spring. It's just a stop. What's the deal with that?

For now I'm just adjusting it so that there's no pulley/cog contact in lowest gear as I would a B-tension. But I have to wonder, is this lack of a spring a downgrade from older designs?
In the past, I'd see the springiness of the B-tension would allow gap distance to close up in high gears (since the larger front chainrings would pull against it harder) I guess that may be irrelevant for my current 1x use though.
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Old 12-16-16, 06:21 AM
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Instructions: https://si.shimano.com/php/download.p...0B-001-ENG.pdf
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Old 12-16-16, 06:27 AM
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Originally Posted by xenologer
Hello
I'm familiar with sizing chains for usual 3x/2x drivetrains; wrapping big+big+1 method to determine minimal length, and the derailer pulley contact check to determine maximum length. typically ending up with not much margin between these and going minimal length.

However, I'm relatively new to 1x drivetrains, and they bring up the question of ideal chain length for shifting performance.
being a 1x, the margin on derailer capacity is huge. a very big difference between minimum and maximum chain length allowable.

so how do I decide? especially given that the chain length will end up affecting derailer body position; which in turn will affect shifting performance -but exactly what effects I am unsure of

shorter chain rotates the cage forward, longer lets it sit further back... which way is better for shifting responsiveness? and this is clearly a much bigger factor than what a b-tension screw will be able to account for alone
perhaps there's an ideal angle for the cage to sit at?
what say the experts?
Thanks
All explained in detail:
Chain length sizing for bicycles with derailleurs

In short:
Both Shimano and SRAM, as far as I know, recommend big-big + 2 whole links (that is 2 inches, or 4 half-links).

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Old 12-16-16, 06:49 AM
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Originally Posted by Slaninar
Yeah I know that.
The question is, when there is major allowable leeway due to high capacity derailer combined with only a single chainring. How going longer or shorter (within the min/max limits) affects shifting performance.
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Old 12-16-16, 06:57 AM
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Originally Posted by cobba
Thanks
Actually I already read that doc before making a thread.
It covers basic setup, but doesn't really address my main question: when there's a large allowable margin for chain length, what effects does going longer/shorter (while remaining within capacity) have on shifting?

From the sounds of things, my particular derailer may not care, since the upper pulley is co-axial with the cage pivot and thus cog/pulley distance is unaffected by chain takeup.

Still, the question remains valid for other derailer designs.

Hypothetical:
Shifting response depends mainly on the distance between cogs and upper pulley.
Suppose we can achieve a good cog/pulley distance in two possible ways, due to a large derailer capacity for the given drivetrain:
A. High b-tension with a shorter chain and the cage rotated forward.
B. Low b-tension with a longer chain and the cage more relaxed.
Which situation is preferable?

Last edited by xenologer; 12-16-16 at 07:05 AM.
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Old 12-16-16, 07:20 AM
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What's preferable is to just follow the length guidelines, adjust the b-tension as needed and ride (or find something else more productive to do). Cold weather can really bring out the OCD in folks.
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Old 12-16-16, 07:49 AM
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Originally Posted by xenologer
Yeah I know that.
The question is, when there is major allowable leeway due to high capacity derailer combined with only a single chainring. How going longer or shorter (within the min/max limits) affects shifting performance.
Chain too long usually makes RD's job tougher - more chain to wrap, yanking on bumps.
Chain too short - makes the RD stretched out a lot.

While with a double, or a triple, a big-big combo is not advised, and probably never used for long, with 1x drivetrains, it is a logical choice for steep climbs.

So big-big plus too, leaves the RD cage optimally bent and without too much slack chain to "gather".
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Old 12-16-16, 08:28 AM
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Originally Posted by cny-bikeman
What's preferable is to just follow the length guidelines, adjust the b-tension as needed and ride (or find something else more productive to do). Cold weather can really bring out the OCD in folks.
Don't be mean please.
If you didn't want to contribute you didn't have to say anything at all.
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Old 12-16-16, 08:37 AM
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Originally Posted by Slaninar
So big-big plus too, leaves the RD cage optimally bent and without too much slack chain to "gather".
I actually am not sure this is 'optimal', certainly it is 'safe' as it assures the chain is minimally long enough for all possible combos.

Initially I had it set as Bigbig+1link and found shifting to have issues climbing into lowest gear (big cog). (single front sprocket)
So I measured the max length that the derailer would take up, then took the average between min/max.
This seemed to put the rear derailer at a less stretched out position overall, allowed b-tension to be reduced, and shifting to low gears went smoother.

So... in the initial state, the derailer was angled as if I was running on the big sproket of a triple at all times. But after putting it to the 'average' length, it was acting more like I was running on the middle ring of a triple. (which seems to make sense, since its a single ring, you'd want it to perform the same way the most used ring of a 3x drive would be used)

Last edited by xenologer; 12-16-16 at 08:43 AM.
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Old 12-16-16, 08:43 AM
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Originally Posted by xenologer
I actually am not sure this is 'optimal', certainly it is 'safe' as it assures the chain is long enough for all possible combos.

Initially I had it set as Bigbig+1link and found shifting to have issues climbing into lowest gear (big cog). (single front sprocket)
So I measured the max length that the derailer would take up, then took the average between min/max.
This seemed to put the rear derailer at a less stretched out position overall, allowed b-tension to be reduced, and shifting to low gears went smoother.

So it seems to me that, having the springs in the derailer be under less tension overall may make for smoother shifting. But don't go so loose that you end up with lots of chain slap.
If that were the case - springs as loose as possible i.e. chain as long as possible, then big-big + 5 full links would probably be better. My experience is that longer chain (that is too long, even if it doesn't exceed the RD's chain wrap capacity) makes for slightly slower shifting.

If your RD works better with longer chain, then make it as long as possible - put it in the smallest rear, then guide the chain through the RD and cut it to size just to clear the top RD pulley. You can always further shorten it.
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Old 12-16-16, 08:47 AM
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Originally Posted by Slaninar
If that were the case - springs as loose as possible i.e. chain as long as possible, then big-big + 5 full links would probably be better. My experience is that longer chain (that is too long, even if it doesn't exceed the RD's chain wrap capacity) makes for slightly slower shifting.

If your RD works better with longer chain, then make it as long as possible - put it in the smallest rear, then guide the chain through the RD and cut it to size just to clear the top RD pulley. You can always further shorten it.
See edit:
Rethinking it, I don't think its actually a case of looser springs;
but of the derailer angle more closely approximating that of a middle ring on a triple, as opposed to the big ring on a triple.
(this is a 1x drive)
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Old 12-16-16, 08:59 AM
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Does the bike have rear suspension?
If it does, you should get the chain length with the suspension compressed to allow for 'chain growth'.

Post a photo of the derailleur attached to the bike, people often attach Shadow derailleurs incorrectly.
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Old 12-17-16, 08:17 AM
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I recently converted to a 1x9 on my beater. (44 & 11-34) I used big-big plus 2 to size the chain. Adjusted the derailleur (cable tension and b-screw), the same way I'd adjust any rear derailleur. The drivetrain shifts are crisp and precise. How and why would I want to improve on that?

Last edited by coupster; 12-18-16 at 08:16 AM.
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Old 12-18-16, 08:14 AM
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Originally Posted by xenologer
Don't be mean please.
If you didn't want to contribute you didn't have to say anything at all.
You asked for opinions, and I gave you mine, and it was more wry humor than mean. If you want to filter what your receive so that you only hear what you want then consult with your friends rather than a public forum.

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Old 12-18-16, 08:32 AM
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Originally Posted by xenologer
See edit:
Rethinking it, I don't think its actually a case of looser springs; but of the derailer angle more closely approximating that of a middle ring on a triple, as opposed to the big ring on a triple. (this is a 1x drive)
As you have already stated that your derailleurs pulley is centered on the derailleur pivot there is no reason for the angle to make a difference, and a "middle chainring" could easily be anywhere from 32 to 42 teeth.
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Old 12-18-16, 08:43 AM
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Originally Posted by cny-bikeman
As you have already stated that your derailleurs pulley is centered on the derailleur pivot there is no reason for the angle to make a difference, and a "middle chainring" could easily be anywhere from 32 to 42 teeth.
Point
that's my fault for being unclear actually

I have 2 sets of test anecdotes here:
the positive result came from adjustments on an old STX

while the current derailer that's being finnicky is a newer Shadow type (with the co-axial pulley)
after changing the chain length on this one, there does appear to be no discernable effect.

Overall, I do think I like the older design better. After following the Shadow instructions for cog/pulley distance on the low gear, it has much larger pulley distance in high gears compared to my older derailers.
Springy b-tension that moves around, seems more accomodating than the new fixed position type.
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Old 12-18-16, 08:49 AM
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Originally Posted by cny-bikeman
You asked for opinions, and I gave you mine, and it was more wry humor than mean. If you want to filter what your receive so that you only hear what you want then consult with your friends rather than a public forum.
Why would my friends only tell me 'what I want to hear'? We know each other well enough that it's acceptable to be brutally honest as well as to make "wry humor".
In contrast, I feel a public forum should be a place where politeness ought to be a priority.
...I guess people come from all kinds of different social backgrounds.

But hey, it's the holidays and I don't want to get into a fight, so,
you may have the last word on this matter if you wish, I won't pursue it.

Last edited by xenologer; 12-18-16 at 08:52 AM.
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Old 12-18-16, 09:18 AM
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Originally Posted by Slaninar
In short:
Both Shimano and SRAM, as far as I know, recommend big-big + 2 whole links (that is 2 inches, or 4 half-links).

I did half that on my SRAM Rival 1x build.

48 in the front, 11-42 in the back. Shifts fine. Very crisp for such a long DR and wide gap.
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