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Please help tweak my SS chainline!

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Please help tweak my SS chainline!

Old 12-19-09, 01:27 AM
  #1  
Sincitycycler
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Please help tweak my SS chainline!

Here's what I run: 180mm Dura-Ace square taper crankarms with a Shimano UN-54 68mmx107mm bb. I have the chainring mounted on the inside of the road spider and my chainline is 39mm- not bad but a tad inside.

In order to get the prescribed perfect SS chainline (rear spacing 120mm) of 42mm, do I simply need to get a UN-54 68x110?

Suggestions welcome
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Old 12-19-09, 01:39 AM
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You could also space out the rear wheel the 3mm. A change that small wouldn't really require redishing.

Or you could also just live with it. If it doesn't cause you any trouble, and doesn't make undue noise, what's the harm?
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Old 12-19-09, 01:48 AM
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Does going to a 3mm wider bb mean that it expands 1.5mm per side?
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Old 12-19-09, 02:04 AM
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Originally Posted by Sincitycycler View Post
Does going to a 3mm wider bb mean that it expands 1.5mm per side?
yes.
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Old 12-19-09, 02:35 AM
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"Does going to a 3mm wider bb mean that it expands 1.5mm per side?"

No. 107mm and 110mm have the same drive side length.

110mm bottom brackets are more symmetrical than the 107mm, in that the non drive side sticks out further, at least for Shimano bottom brackets.
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Old 12-19-09, 02:56 AM
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Hooray! Sheldon Brown to the rescue!

Bottom Bracket Overall Length Drive Side Length
Sugino/Tange 68-103 103mm 18mm
Shimano UN54 68-107 108mm 20mm
Shimano UN54 68-110 111.5mm 20mm
Shimano UN54 68-113 114mm 22.5mm
Shimano UN54 68-115 115.5mm 23.5mm
Shimano UN54 68-118 118.5mm 25mm
Shimano UN54 68-122 123mm 28mm
Shimano UN54 68-127 128mm 30mm
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Last edited by Sincitycycler; 12-19-09 at 03:44 AM.
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Old 12-19-09, 06:04 AM
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Originally Posted by Sincitycycler View Post
I have the chainring mounted on the inside of the road spider and my chainline is 39mm- not bad but a tad inside.
First suggestion: move the chainwheel to the outside of the road spider. If chainline is now outside, use freewheel spacer to bring cog/freewheel further out. https://www.bicycleresearchtools.com/access.html - link to freewheel spacers scroll down Make sure there is enough thread for freewheel/cog on hub.

Second suggestion: Keep chainwheel on inside of road spider but use freewheel spacer to move bottom bracket further out. Make sure enough threads exposed on non-driving side to hold bottom bracket firmly.
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