Chainline effects of double-to-triple?
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Chainline effects of double-to-triple?
I'm taking off the double crank & axle that came stock with my bike and installing a triple crank and axle. All parts are Shimano. What will I be doing to my chain line? Thanks.
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Probably moving it over a good 10-12 mm. You won't have the same range of gears with the top and now middle chainrings since there will be another chainring in the mix.
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The difference isn't that great at all. The nominal chainline for a double is 42-44 mm (between the 2 chainrings) where as the nominal chainline for a triple is 46.5 mm (middle ring). A typical double BB is 108 mm wide where as a typical road triple BB is 113 mm wide. Its possible sometimes to fit a triple crankset to a double BB but the critical thing you need to watch for is clearance for the inner ring from the chainstay.
Regards, Anthony
Regards, Anthony
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I had some issues with this myself. The small chainring would clear the frame no problem, but the deraileur would not travel that far back. I switched to the 118.5 BB and all worries were gone.
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According to Sheldon's page on chainlines, if you move from a road double crankset to a road triple crankset and you also change to the Shimano's recommended bottom bracket, you can expect your chainline to be moved over only 1.5mm, a very small amount.
Some stats:
road double crankset = 43.5mm chainline
road triple crankset = 45mm chainline
https://www.sheldonbrown.com/chainline.html
Some stats:
road double crankset = 43.5mm chainline
road triple crankset = 45mm chainline
https://www.sheldonbrown.com/chainline.html