A Bottom Bracket/Chainline question

"TomYoung" <[email hidden]> wrote in message
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Quoted message said:

Hi all:

I have a complete 9-speed Ultegra triple setup that I mount on my
roadbike once a year for a very hilly Century. Now, I'm thinking of
getting a touring bike and mounting the Ultegra setup on that, but the
bike I have in mind has 135mm rear dropout spacing instead of the
130mm on my road bike.

The touring bike frame will probabaly have longer chainstays.

Quoted message said:

The Ultegra bottom bracket has a listed length of 118.5mm. I've never
measured the chainline when the triple setup is mounted on my current
road bike, but shifting has generally been fine, so I'm assuming, at
least for sake of this discussion, that the chainline is "just right."

I recently installed Shimano triples on 2 different bikes. They both
theoretically required 122mm BBs. I had to go to 118mm on both of them.

You can use a spacer behind the "fixed" or right hand cup on most bottom
brackets to adjust the chainline..

Quoted message said:

Offhand, it seems like the chainline could be out of whack if I mount
the Ultegra stuff on a bike with 135mm rear spacing since the cogs are
now going to be sitting 2.5mm to the right of where they'd be on my
current road bike, meaning I should be going to a longer bottom

bracket

Quoted message said:

axle, which doesn't seem to be available from Shimano.

2.5mm shouldn't make that much difference on the chainline with a lomger
chainstay. Generally you should avoid extreme crossovers for good chain
life, big - big, or little-little sprockets.

Quoted message said:

Am I thinking about this correctly? Or is there any general approach
to these chainline issues without actually fitting components to the
bike?

I had to install the cranks on both frames. in my situations.

Quoted message said:

TIA.

Tom Young

Chas.