chainline during a drivetrain upgrade
howdy. first big mechanical project on my bike, hopefully i'm not going to miss anything big.
one of the main things i'm worried about is how the upgrade is going to affect my chainline. i'm moving from sora 8x3speed to 105 9x2 speed. I should be able to use the same freehub on the back and just throw on the new cassette, right? so assuming that's the case, what will I need to take into account chainline wise moving from 8 sprocket to 9 sprocket cassette, and triple to double crank in the front? thanks for help.
The change from 8 speed to 9 speed doesn't alter the chainline that's required for the chainrings.
Nominaly a triple will use a 113-118 mm BB spindle for a 46.5 mm chainline measured to the middle chainring. A double will use a 108 mm BB spindle for a 44-45 mm chainline measured to the middle of the 2 chainrings. Thats the theory anyway but the measured reality can be different.
Short answer is you will need a 108 mm BB.