Understanding chainline when messing with drivetrains (1 by etc)
#1
Understanding chainline when messing with drivetrains (1 by etc)
Hi all
I have a few older bikes that this forum has helped me with. I've done various non-approved things to them and curious to find different results. Both have been extensively tuned, dialed, ridden, tuned. As I am about to set up another bike from scratch I'm wondering about Chainline.
Bike 1: 1969 Bottecchia
Nervar Star crank with 1 wheel installed, 8 speed 12-32 XTR cassette, 80's Dura Ace rear derailleur. Suntour power downtube shifter.
Front Chainline: 51mm
Rear Chainline: 42mm
This bike "should not" work. The chainline is off, I'm pushing the Dura Act past its capacity, I spread the rear from 120>130mm. But it shifts like absolute heaven, stays in gear, just a happy ride.
Bike 2: 2014 Ritchey Swiss Cross
Truvative Elita crank with 1 wheel installed, 9 speed SRAM 11-34, 90's Dura Ace rear derailleur. Gevenalle Audax friction shifters.
Front Chainline: 42mm
Rear Chainline: 43mm
This bike "should" work. I am pushing the rear derailleur again yes, but the chainline is "perfect". This bike is fussy about staying in gear, it hunts about in the mid range.
Park Tool's article on chainline says "if it ain't broke" and I'm down with that. Not messing with the Bottecchia. But when I'm looking to set up another bike from scratch and can choose any chainline I please... I'm wondering if there is any reason to consider something other than the "perfect" chainline.
Thoughts?
I have a few older bikes that this forum has helped me with. I've done various non-approved things to them and curious to find different results. Both have been extensively tuned, dialed, ridden, tuned. As I am about to set up another bike from scratch I'm wondering about Chainline.
Bike 1: 1969 Bottecchia
Nervar Star crank with 1 wheel installed, 8 speed 12-32 XTR cassette, 80's Dura Ace rear derailleur. Suntour power downtube shifter.
Front Chainline: 51mm
Rear Chainline: 42mm
This bike "should not" work. The chainline is off, I'm pushing the Dura Act past its capacity, I spread the rear from 120>130mm. But it shifts like absolute heaven, stays in gear, just a happy ride.
Bike 2: 2014 Ritchey Swiss Cross
Truvative Elita crank with 1 wheel installed, 9 speed SRAM 11-34, 90's Dura Ace rear derailleur. Gevenalle Audax friction shifters.
Front Chainline: 42mm
Rear Chainline: 43mm
This bike "should" work. I am pushing the rear derailleur again yes, but the chainline is "perfect". This bike is fussy about staying in gear, it hunts about in the mid range.
Park Tool's article on chainline says "if it ain't broke" and I'm down with that. Not messing with the Bottecchia. But when I'm looking to set up another bike from scratch and can choose any chainline I please... I'm wondering if there is any reason to consider something other than the "perfect" chainline.
Thoughts?
#2
Senior Member
My guess is that the longer cable length may have something to do with it. A better chainline should equal better shifting and a quieter drivetrain.
Did you take care to square the cable housing ends, remove burrs, that sorta thing? How fastidious are you when putting your bikes together?
Did you take care to square the cable housing ends, remove burrs, that sorta thing? How fastidious are you when putting your bikes together?
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#4
Senior Member
Evaluate any play in the rear mech parallelogram especially in the middle cogs. Not knowing the individual cog sizes but sometimes the change in cage angle exaggerates any slop.
rear mechs do not live forever.
rear mechs do not live forever.
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#6
Full Member
I dont't think you have a good grasp of chain line. think of it this way if you run a line through the center of the bb and the center of the rear triangle. mesure out th the middle cog of the cassett, or between the middle cogs if an even number of cogs, that number is your perfect chainline. See the atached pict it is for a 5 speed 120 mm rear end 43.5mm chain line , yours should be 130 mm so you would need to add 2.5mm for 46 mm chain line
#7
That is how I measured chainline.
I dont't think you have a good grasp of chain line. think of it this way if you run a line through the center of the bb and the center of the rear triangle. mesure out th the middle cog of the cassett, or between the middle cogs if an even number of cogs, that number is your perfect chainline. See the atached pict it is for a 5 speed 120 mm rear end 43.5mm chain line , yours should be 130 mm so you would need to add 2.5mm for 46 mm chain line
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#8
i built the wheels on both bikes and checked the rear triangle with a park tool frame alignment gauge. Did not check the dropout alignments as I dont have that tool.
#9
Senior Member
I agree that checking dropout alignment would be good. Be also found that some setups are really sensitive to chain length, particularly if your rd spring is a bit weak.
#11
Given that this is friction, and the problem is occurring in the midrange (where presumably the chainline is most perfectly parallel to the bikes centerline), it sounds like the rd simply isnt capable of running the chain where it needs to be. So my hunch is a bent derailleur hanger as nlerner mentioned. If you stand behind the bike, does the cage appear to be in plane with the cogs?
Other thoughts:
Not super clear on just what is happening in the mid range. Is it trying to ghost shift to a higher gear? Have you snugged down the shifter?
Have you tried swapping in a different chain?
Also re chain - I would also double check and be sure you didnt use an 8 spd chain by mistake.
Other thoughts:
Not super clear on just what is happening in the mid range. Is it trying to ghost shift to a higher gear? Have you snugged down the shifter?
Have you tried swapping in a different chain?
Also re chain - I would also double check and be sure you didnt use an 8 spd chain by mistake.
Last edited by due ruote; 08-23-23 at 08:49 AM.
#13
Senior Member
Another thing to check, which I learned from [MENTION=170517]rccardr[/MENTION]: that 9-speed SRAM cassette might not quite have spacing compatible with those shifters.
#15
Seņor Member
Have you checked the rear derailleur hanger alignment? That has resolved some poor rear shifting issues I've encountered (although mostly indexed shifting)
This tool makes it easy, but I believe some the C&V community may have cheaper alternatives.
https://www.parktool.com/en-us/produ...-gauge-dag-2-2
This tool makes it easy, but I believe some the C&V community may have cheaper alternatives.
https://www.parktool.com/en-us/produ...-gauge-dag-2-2
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#18
I would suggest putting down all measuring tools for a moment and just use your eyes. With the bike on a stand, middle cog, either chainwheel (try both), spin the pedals backwards at a decent rpm. Look at the RD for any forward/back pulsing. Look down the chain from the back, the chain should be nearly straight.
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59 Allegro Special -- 72 Bob Jackson -- 74 Motobecane Grand Jubile -- 74 Sekine SHS 271 -- 80 Nishiki International
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#19
Should shift fine, all things being friction.
Suggest, like others, that you check dropout alignment but ALSO whether the cage on the RD is bent in or out.
Would also suggest disassembling the RD pulley wheels and giving them a thorough cleaning and lubrication.
Would also suggest checking each individual link on your new chain to ensure that none are binding (new does not always = perfect).
Am curious which DA RD’s you are running on both setups, as your big cogs are significantly beyond any happy place I’ve found with DA’s using normal cages.
Suggest, like others, that you check dropout alignment but ALSO whether the cage on the RD is bent in or out.
Would also suggest disassembling the RD pulley wheels and giving them a thorough cleaning and lubrication.
Would also suggest checking each individual link on your new chain to ensure that none are binding (new does not always = perfect).
Am curious which DA RD’s you are running on both setups, as your big cogs are significantly beyond any happy place I’ve found with DA’s using normal cages.
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#21
Senior Member
I once had shifting problems with an Ultegra RD. Unfortunately, I discovered this at the start of a 24-hour, 360k ride. Normally, I ran that setup (with bar-end shifters) in 8-speed index mode, but switched to friction when I realized indexing wasn’t working. Even in friction, however, shifts were really sloppy. After that ride, when I got around to trying to figure out what was wrong, I realized that I had switched the upper and lower pulleys when previously cleaning and reassembling the RD. Whoops! Not sure if this would be a problem for the DA RD, but it’s worth checking (on the Ultegra the pulleys are clearly marked, but I wasn’t paying attention).