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Old 03-23-09, 01:11 PM   #1
cedricbosch
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Shorter BB spindle to fix chainline?

I converted a cheap-o department store bike into a beater single speed. The only problem is the chainline really sucks. I'm using a single-speed Shimano cog in the back, and a chainring on the middle-ring location of a triple crankset. The problem is that the chainring is too far from the frame. I'd like to bring it closer and I think a shorter BB spindle is the best idea. Short of taking the cranks off, how can I tell what length I have? If you had to guess, what length BB spindle would you choose to move the chainline ~5mm closer to the frame?

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Old 03-23-09, 02:04 PM   #2
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is it possible to use spacers to shift your rear cog out?
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Old 03-23-09, 08:11 PM   #3
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I dont think so- it's a single speed freewheel.
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Old 03-23-09, 08:21 PM   #4
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I don't get it, can't you just pull off the cranks and measure the BB with some calipers?
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Old 03-23-09, 08:24 PM   #5
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Just get a bb with a spindle 10mm shorter than the one you have now
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Old 03-23-09, 08:24 PM   #6
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I don't get it, can't you just pull off the cranks and measure the BB with some calipers?
This is exactly what the OP needs to do.
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Old 03-23-09, 08:25 PM   #7
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Just get a bb with a spindle 10mm shorter than the one you have now
Assuming it's symmetrical. For example 110 shimano cart to 107 bb results in the exact same chainline.
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Old 03-23-09, 08:27 PM   #8
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Assuming it's symmetrical. For example 110 shimano cart to 107 bb results in the exact same chainline.
Gotta guess that's it's not symmetrical too? Not fair...
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Old 03-23-09, 08:33 PM   #9
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Do you know what your current chainline is?
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Old 03-24-09, 07:30 AM   #10
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The normal chain line is 47-48mm from the center of the ST to the tip of a tooth on the big ring. Measure from the side of the ST and add half the ST diameter.
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Old 03-24-09, 08:02 AM   #11
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The short answer is that there's no simple way that I've found to estimate chainline based on BB spindle length. The long answer is that, if you get a shorter BB spindle, you can probably make it work just fine, within a couple mm. Is there any option for respacing and -dishing your rear wheel to fix?
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