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ok so I’m trying to go from 2×9 to 1×9 and just when I thought I was ready to get new NW chainring, I look and see another factor to consider……..chainline!?!?!?
how do I determine why my chainline is and what chainline will my bike except?
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I expect you have found that you need to get your chain ideally running in line with middle cog of the cassette. This minimise the ‘bend’ in the chain line which minimises wear and pedal efficiency, oh and less chance your chain comes off.
If possible look at the teeth on the present chainring. Which side of the teeth are worn most? It should ideally be even. Rarely is but this what your want to achieve.
If you can’t fudge the crank position to move the chainring to best line position then use 2mm chainring mount bolt spacers to reposition the ring on the crank arms.
On my Hope crankset I have a mix of XTR 22T and XT outer rings which necessitates those spaces to align the rings. Also to move the chainrings in board to eek a better chainline for the gears that I am going to grind on.
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So if I understand this correctly, it’s more of a trial and error thing? You basically eyeball it and use 2mm spacers to correct it either way?
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Yes put crank on and look down the chain, if still room to move then take bb spacer ring out (put on other side of bb). It is a faff. If can’t move crank the use 2mm chainring spacers. Be aware you can only use 1 2mm per chain ring bolt. Be sure 2mm spacers and chain ring sit secure if you do do this. Depending on bike frame Q factor and crankset used you will not have ideal alignmentment.
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You could always just measure it first if you’re trying to achieve a certain chainline.
When in doubt, Sheldon Brown it out: http://www.sheldonbrown.com/chainline.html
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Thanks @Endopro for starting this thread!
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