TAS FOUND

nathanm

nathanm

Eats Squid
moorey said:
@nathanm, I’m not 100% convinced new/different cranks are going to solve your issue.
You’re running in place of the middle ring on current triples? Is the ring seemingly too far in or out? Remind me what cranks you’re currently using?
Click to expand...
yeah nor am I now.

i tried an experiment last night and changed to a different set of cranks (Raceface unknown) which appear to be another "double" set. however the spindle is attached to the non drive arm allowing me to move the chainring closer towards the frame. This produces a minor improvement so it's pretty much certain the issue is just related to chain line and I need to move the chain ring further "in".

The cranks I want to use are Shimano SLX, but could be up to 10 years old.

I've got some 2mm "spacers" coming for the cranks but I reckon I could need 2-3x times that. would be nice if they weren't so expensive so I could just grab a bunch to try.
 
D

Daniel Hale

She fid, he fid, I fidn't
nathanm said:
The cranks I want to use are Shimano SLX, but could be up to 10 years old.

I've got some 2mm "spacers" coming for the cranks but I reckon I could need 2-3x times that. would be nice if they weren't so expensive so I could just grab a bunch to try.
Click to expand...
this seems a lot of inward movement if you have them on the middle ring, does the chainring side bb have a spacer on you can remove & place on non drive side..on the 3x does it have inner ring on small holes, then middle ring then crank then outer ring on same holes as middle ring
 
nathanm

nathanm

Eats Squid
Daniel Hale said:
this seems a lot of inward movement if you have them on the middle ring, does the chainring side bb have a spacer on you can remove & place on non drive side..on the 3x does it have inner ring on small holes, then middle ring then crank then outer ring on same holes as middle ring
Click to expand...
yeah agreed. it should really just work as is but doesn't with the chain "falling" down the cassette when backpedalling, which is a symptom of a chainline issue, particularly a front chainring too far "out" of alignment.
Yep crankset is standard bolt on granny, then middle and outer sharing the same hole.
A few people believe this is a standard Shimano "feature" but I refuse to accept this without doing due diligence to try and eradicate it for nothing more than my own satisfaction.
 
D

Daniel Hale

She fid, he fid, I fidn't
nathanm said:
A few people believe this is a standard Shimano "feature" but I refuse to accept this without doing due diligence to try and eradicate it for nothing more than my own satisfaction.
Click to expand...
isn’t that because whilst a cassette midpoint is 44-45mm for 11 spd, didn’t shimano initially settle on 46-7mm chainline, but then sram realised you can’t clear more than a 28t front ring. so settled on 49-50mm chainline, forget the boost pic below
360474
 
moorey

moorey

call me Mia
As stated many times....the chain dropping off the low gears back pedaling is just a thing that Shimano does.
Go...ewwww...sram if you don’t want this. Just a derailleur is needed probably. Your cassette, chain and shifter are compatible.
 
nathanm

nathanm

Eats Squid
moorey said:
As stated many times....the chain dropping off the low gears back pedaling is just a thing that Shimano does.
Go...ewwww...sram if you don’t want this. Just a derailleur is needed probably. Your cassette, chain and shifter are compatible.
Click to expand...
No. I refuse to believe this is true. Shimano is far superior to SRAM and I cannot believe they haven't allowed for retro fitting of 11 speed gear and/or not properly thought through their chainline design. 2020 technology should easily fit onto 2012 bikes (he says firmly tongue in cheek)

The issue is going to be made worse by the fact the bike is also 9x135mm rear which (I think) makes the cassette midpoint again much further in? or I may be wrong, I'm really learning on the fly here.
 
moorey

moorey

call me Mia
You are wrong on last point. 135x9 is same as 135 thru axle is the same as 142.
142 just has channels in frame to locate axle. Same hub otherwise.
I have bikes much older than 2012 working with 11sp. Qr 135, bolt up 135, and 142x12 (latter is 2013 though)
I’m tapping out. I wish you well.
 
rangersac

rangersac

Medically diagnosed OMS
Pics of the crankset I reckon for diagnosis. It would be helpful to know on what cassette cog is the chainline currently straightest as this would give a clue as to whether spacers might be the go. Also what chain are you using? If it's a Shimano 11sp they are unidirectional so check it's not around the wrong way.
 
D

Daniel Hale

She fid, he fid, I fidn't
i have read some threads on this, seems some sram users have the exact same problem, chainnfalls down when back-pedalling..2 diff friends with 1 friend setting up both bikes, his friends does it, his bike doesn’t..same drivetrain

when you come to think of it how does it not fall inward:
you have a clutch derailleur which adds friction to the derailleur moving forward, when you back pedal the derailleur is resisting your movement, slackening the chain on a cassette which is designed to shift down between cogs seemlessly & add in the angle on the chain on your chainring to the top cog, why woudln’t it fall down

then again almost no 10 spd users reporting the same issue
 
wkkie

wkkie

It's Not Easy Being Green
How many gears does the chain drop down?

I found that once everything wears in a little the problem isn't as pronounced.
 
nathanm

nathanm

Eats Squid
wkkie said:
How many gears does the chain drop down?

I found that once everything wears in a little the problem isn't as pronounced.
Click to expand...
SLX cranks, tend to lose a minimum of 2. RF cranks only drops 1, occasionally 2.

keeping in mind the bike hasn't actually left the stand yet as I work on the issue at hand.

I also need to take a link out of the chain, but the stupid bloody KMC quick link is absolutely jammed in there and I can't get it off by hand, even using the gear cable trick.
 
wkkie

wkkie

It's Not Easy Being Green
That drop doesn't sound too excessive. See how you go with your spacers and once things wear in a little. Should be right. I found it very rare to backpedal in the big gears on the trail anyway...

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