fixed gear chainline--double checking

autopi said:

so what are my options? i would like to avoid having to re-dish the
wheel/replacing the BB if possible.

If you move the wheel to the left, re-dishing is needed, so that's
out. If the left crank has enough clearance with the stay, and the BB
isn't one of the old multi-piece unsealed units, you might be able to
add a 2mm spacer between the right flange and the BB shell, but that
sometimes won't work. The spacers aren't hard to get; if all else
fails, take the sprockets off of an old freewheel and use one of the
spacers that were between them. (I've seen a *sprocket* used in one
memorable instance, but for reasons that should be obvious, it's not
the kind of thing I'd recommend.)

Quoted message said:

do i need to
put a spacer in on both sides?

Good grief, no! In fact, if there's a lockring securing the cup on
the left side, you probably can't use the spacer trick anyway.

Quoted message said:

or would it be better (or
possible/advisable?) to get the LBS to put in a spacer on the BB so
that the chainring sits out 2mm further?

It *may* be possible, if you have enough clearance where it's needed,
and if the BB is a sealed unit.

There's one other sometimes-useful dodge. Some multi-piece BB
assemblies have an axle that's longer on one side than the other. If
the long side is presently on the left, swapping it end-for-end *may*
put the chainline where you want it. Or this may make it worse.

Good luck.
--
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autopi said:

hi, i know there's a bit of stuff on this topic already in the archives
and on sheldon's website (very helpful!), but i wanted to double check
to see what recommended options are.

i have an old road bike converted to a fixie. it's spaced at 126mm. i'm
using the smaller chainring, on the inside of the spider. this measures
out at maybe a tad over 41mm. (it's hard to get super precise, b/c it's
hard to know where, exactly, the "middle" of the seat tube is.)

the rear wheel is a formula flip-flop hub, with a dura-ace cog &
lockring. per my own measurements and per the info on sheldon's charts,
it sits at 43mm.

thus, i have the cog outboard of the chainring by somewhere between
1.5-2mm. not a lot, but probably worth resolving, seems to be the
consensus.

I don't think it's a big deal .....but put the ring on the outside of
the spider...

Quoted message said:

so what are my options? i would like to avoid having to re-dish the
wheel/replacing the BB if possible. i want to keep it cheap, and i
don't know how to re-dish the wheel mysel (every time i touch a spoke
wrench, it's bad news for the wheel.) can i simply put a 2mm spacer in
behind the locknut on the drive side and be done with it? do i need to
put a spacer in on both sides? or would it be better (or
possible/advisable?) to get the LBS to put in a spacer on the BB so
that the chainring sits out 2mm further?

autopi said:

(it's hard to get super precise, b/c it's hard to know where, exactly, the "middle" of the seat tube is.)

Hmnn - no it's not. You can know with some precision in fact, via a
semi-direct measurement.
1) Meaure the seat tude diameter with a micrometer.
2) Measure from your chainring to the FAR side of the seat tube with
said micrometer.
3) Subtract 1/2 the diameter of the seat tube and you have an exact
chain line measurement.

"Anthony A." <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

autopi said:

(it's hard to get super precise, b/c it's hard to know where, exactly,
the "middle" of the seat tube is.)

Hmnn - no it's not. You can know with some precision in fact, via a
semi-direct measurement.
1) Meaure the seat tude diameter with a micrometer.
2) Measure from your chainring to the FAR side of the seat tube with
said micrometer.
3) Subtract 1/2 the diameter of the seat tube and you have an exact
chain line measurement.

And remember, it's better to be off with the chain ring a mm or two to
the right of the cog than to the left.

Phil H

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In article <[email hidden]>,

Phil Holman piholmanc@yourservice said:

And remember, it's better to be off with the chain ring a mm or two to
the right of the cog than to the left.

_ Why exactly? I'm not trying to be smart, just willing to
learn. Is it because of BB flex?

_ Booker C. Bense

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"Booker C. Bense"
<[email hidden]> wrote in
message news:[email hidden]...

Quoted message said:

-----BEGIN PGP SIGNED MESSAGE-----

In article <[email hidden]>,

Phil Holman piholmanc@yourservice said:

And remember, it's better to be off with the chain ring a mm or two to
the right of the cog than to the left.

_ Why exactly? I'm not trying to be smart, just willing to
learn. Is it because of BB flex?

It is. BB flex to the left is higher because chain tension adds to the
deflection. Deflection to the right is reduced by the chain tension. You
don't have to take my word for it, hold your bike and stand on each
pedal and see for yourself.

Phil H