somebikeguy 

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?

Piff 

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?

somebikeguy 

I hadn't thought of the cable length this is a good point.

I am hella fastidious and use The Good Stuff (eg quality cables and housing) wherever possible.

repechage

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.

Piff 

Oh, and just to cover our bases, you're sure that the wheel is properly dished and the frame alignment isn't buggered?

trainman999

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

somebikeguy 

That is how I measured chainline.

somebikeguy 

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.

nlerner

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.

somebikeguy 

Appreciate shining a light on the RD. Since it was manufactured in my lifetime and a trusty DA I had frankly ignored it. Will take a closer look and swap another RD as a test.

due ruote 

Given that this is friction, and the problem is occurring in the midrange (where presumably the chainline is most perfectly parallel to the bike’s centerline), it sounds like the rd simply isn’t 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 didn’t use an 8 spd chain by mistake.

somebikeguy 

Chain is a new SRAM PC971 9 speed. I will check the derailleur and its hanger for sure.

nlerner

Another thing to check, which I learned from @rccardr: that 9-speed SRAM cassette might not quite have spacing compatible with those shifters.

somebikeguy 

They are friction shifters. The Audax uses a Dia Compe ENE. That said I realize the greater spacing on an 8sp will friction shift better than 9sp.

CO_Hoya 

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

somebikeguy 

Only alignment tool I own is park ***-2. This wknd a buddy loaning me dropout alignment kit.

somebikeguy 

Lolol the name of the tool was censored and I understand why. Foxtrot Alpha Golf - 2

droppedandlost 

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.

rccardr 

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.

Reynolds 

Chainstay length also could be a factor in chainline issues - longer chainstays would be less sensitive.

nlerner

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).