Chainring Pitch Standard?

[Luke Forward]

Hi folks, I own a GIANT Flight Mini 3 '07(same modle as Escape Mini 3
sold in Japan).
This is a 20" bike with single chainring(48T) and 11T-28T cassette,
130mm rear OLD. I ride high cadence and 48T chainring is not good for
me so I changed the crankset to a Race Face Ride XC ISIS(44T-32T-22T)
with the small ring off, which makes it a doble. The problem is, even
I've noticed the chainline effect and I installed a shorter ISIS BB
68-108(the shortest I could find in Taiwan), the front chainline still
goes a little outward whitch makes chain drop happens so easily at
lowest gear.
My next step is to move the chainring to the inside of crank spider
for minor chainline adjustment. And this may affect the distence
between two chainrings. So far I can't find any resources about this,
any ideas?

[Tim McNamara]

In article
<e5925174-75c9-40d3-9166-619976b9cc2f@k10g2000prm.googlegroups.com>,
Luke Forward <lukefoward@gmail.com> wrote:

> Hi folks, I own a GIANT Flight Mini 3 '07(same modle as Escape Mini 3
> sold in Japan).
>
> This is a 20" bike with single chainring(48T) and 11T-28T cassette,
> 130mm rear OLD. I ride high cadence and 48T chainring is not good for
> me so I changed the crankset to a Race Face Ride XC ISIS(44T-32T-22T)
> with the small ring off, which makes it a doble. The problem is, even
> I've noticed the chainline effect and I installed a shorter ISIS BB
> 68-108(the shortest I could find in Taiwan), the front chainline
> still goes a little outward whitch makes chain drop happens so easily
> at lowest gear.
>
> My next step is to move the chainring to the inside of crank spider
> for minor chainline adjustment. And this may affect the distence
> between two chainrings. So far I can't find any resources about this,
> any ideas?

Well, first, that's not pitch. That's chainring spacing. Pitch is the
distance between the centers of the valleys between the teeth and is a
standard 1/2" on all bikes except the old Shimano 10 mm pitch stuff.

If you move the outer ring inboard, you will need to move the inner ring
inboard as well *if* you're going to shift between them. If you're just
using the 44T and ignoring the 32T ring, then don't worry about it.
Your single speed crank probably had the chainring much more inboard
than a multi-ring crank would have it, and the frame was probably
designed with this in mind.

You must ride a *really* high cadence if a 48 x 11 on a 20" wheel was
too high- that's only an 87" gear! Your 44 results in an 80" gear.