Chain line

[Sweep]

I realise that this question is like walking into the lions' den in view of the level of (very helpful) expertise on here, but:

Just how important is "chain line" when selecting bits?

I have done a fair amount of tinkering, even bike building (bar installing headsets or building wheels) but so far, so far as I am aware, have managed to avoid any issues with a subject which, whenever I have looked at it, propels me back to the horror of O level maths and trigonometry.

I am currently building up an old 90s hybrid as a fast-ish city bike and of course keep coming across this in spec sheets, most recently in the specs for a front mech.

As I said, be gentle - I'm not that techie even though (book firmly in greasy hand) I do pretty much all of my own bike maintenance.

[NATURAL ANKLING]

Hi,

If you bare in mind that as soon as you change gear away from a perfect chain line its not perfect.
Getting it within a say 4-5 mm reduces chain wear and problems with changes even unshipping.
You should find everything you want here just marry up the parts you want to use in the tables -

http://www.sheldonbrown.com/chainline.html

http://www.sheldonbrown.com/bbsize.html

[gloomyandy]

An interesting article on how the wider (135mm) OLN used for road bikes with disc brakes impacts chain line and the possible problems:
http://www.bikerumor.com/2012/11/28/tec ... -shifting/

[mjr]

Matters more if you have a chain guard fitted: too far out and it'll foul the guard. Other than that, I don't worry as long as it's reasonably near.

[mercalia]

I think chainline can be an issue with front changer and it not able to swing in far enough?

[531colin]

Basically, there is "road" stuff and there is "MTB" stuff.
MTB chainline is a bit further out, so the chain clears a big tyre.....so the mech. sits further out, too
So an MTB chainset has an MTB chainline, and it will play nicely with an MTB front mech., which also fits MTB chainring sizes.
Road chainset has road chainline, will play nice with a road mech., which is also curved at about the right shape for (bigger) road chainrings.
Then, road and MTB front mechs. have a different cable pull.....why? because they can! but if you forgo front indexing, it doesn't matter.
There is also "flat bar road"stuff....basically, flat bar shifters with a "road" cable pull....I think!
Stronglight (eg) "touring triples" have a road chainline, if that helps at all.

[Valbrona]

You tend to only notice chainline problems when you have a system that doesn't work.

[gloomyandy]

Not all manufacturers use a different pull ratio for road and MTB front mechs. SRAM use the same (which is nice). They also make a version of the road chainsets with a more MTB like chain line, this is intended to be used with road bikes that make use of disc brakes and so have a wider OLN.

Aren't bikes nice and simple!

[al_yrpal]

If you get a new chain and hold it up horizontally with the pins vertical it will form a curve because of the clearances in the rollers and pins. The droop over a distance between the bottom bracket and rear wheel hub will be a couple of inches or more. That will clearly illustrate how tolerant chains are of a crooked chainline, indeed they are made like that deliberately to accomodate the misalignment that occurs on bicycles.

Al