Chainline woes

Oh god this week has been a chore - trying to get bikes to work, shift and brake properly.

Latest issue is chainline.

I'm interested to hear how far the largest ring "should be" from the right stay?

Over the years (and also installing old cranks with soft/used tapers, cranks can get closer and closer to the chainstays.

Was fiddling last night and one stock bike has at least 8-10mm of distance between outer ring and chainstay whereas another has literally about 4mm.

Just wondering if there was such a standard? They are all using std drive (non of this compact silliness).



Also....



Any tips on getting an m900 rear mech to shift "ok" on an xc pro block. Mine doesnt (as expected really)...

Funny you should mention that, I have just been looking at http://www.sheldonbrown.com/chainline.html
which may be of some use to you.

I am also having woes trying to figure out the chainline for my RC500 at the mo, I bought a 113mm BB I am using Race face Turbine DH cranks and have a 44T big ring (from memmory). My problem is the design of the pace swing arm means it gets very close to grinding on the big ring, approx 5mm space between them without a chain on.

If I move the chainline out with a wider BB axle then the chainline on the rear is very much tainted towards the smaller end of the cassette as apposed to keeping a central line...possibly not so bad on a DH bike, but im not sure.

I am also wondering if I should be using a smaller big ring, around a 40T just to move it away from the swingarm.

tbh, I think I need to play with it a bit in order to decide but at the moment it is baffling!

(sorry not much help on your woes!)

you want the center of the chainset ( middle ring on a triple ) and the center of the cassette , if its eight speed its the gap between 4th and 5th to be in alignment . it doesnt need to be mm perfect but as close as you can get it

run a straight edge along the outer chainring back to the cassette to measure against . i use a length of string

Awesome Perry cool.

Most of my stuff is 7 speed?

Roughly speaking (for MTB triple), middle chainring should line up with middle of cassette. However, it gets more complex if you have a very wide (34.9mm) seat-tube and/or very widely spaced chainstays as your f.mech may not cover the granny ring or your crank arms may foul the stays. I guess on the flip-side a 28.6mm f.mech may not cover your outer ring if the BB axle is too long...

Anyhoo, outer ring to chainstay distance is not really a measurement of chainline, rather a symptom of.

If you measure your middle chainring to seat tube centre, in an ideal world it would be 48-50mm

M900 on XC Pro, try putting the cable the other side of the clamp bolt ?

Flufy Chicken...

What do u mean?

Normally you clamp the gear cable down (on the rear mech) on the lower side of the bolt along the designed line thingy bob as normal.
Instead try clamping it down on the higher side of the bolt.

It may work as it alters the amount the rear mech will move.


If you need picture I can mash something up.

You are using XC Pro/Comp thumbies ?

EDIT quick piccy...

RED = normal
Yellow = Give it a go, may work... may make it worse

FluffyChicken":32c49sr8 said:

M900 on XC Pro, try putting the cable the other side of the clamp bolt ?

Click to expand...

IIrc Campag did this with some of their rear mechs. One way it worked with 8 speed and the other worked with 9. It's all to do with the leverage. Allegedly.