i recently went to a single ring up front. when im in my lowest gear, its pretty obvious how much the chain is actually going sideways to make it all the way in to that rear cog. so i got to measuring and found out that a 50mm chain line is stupid. if you know otherwise, please let me know.
this is all referring to the below diagram. as you can see, the front ring is 50mm from the middle of the bike (aka, a 50mm chainline). a standard rear end is 135mm between the droputs, meaning that each drop out is 135/2 = 67.5mm from the center of the bicycle. if you draw the ideal chainline (perfectly straight) back from the front ring, you find that this intersects the rear at 67.5-50 = 17.5mm from the rear dropout. it would make sense that this "perfect chainline" would be when you are in the middle cog on the cassette. a standard 9 speed cassette has its middle cog about 23mm from the dropout, meaning that a 50mm chain line is about 5mm too far out.
So i want to fix this on my bike. shimano has you put in a 2.5mm spacer between the bb cup and the bb shell. can i move this spacer to the non-drive side to move my chainline in 2.5mm? anyone have any experience with this or any wisdom to add?
this is all referring to the below diagram. as you can see, the front ring is 50mm from the middle of the bike (aka, a 50mm chainline). a standard rear end is 135mm between the droputs, meaning that each drop out is 135/2 = 67.5mm from the center of the bicycle. if you draw the ideal chainline (perfectly straight) back from the front ring, you find that this intersects the rear at 67.5-50 = 17.5mm from the rear dropout. it would make sense that this "perfect chainline" would be when you are in the middle cog on the cassette. a standard 9 speed cassette has its middle cog about 23mm from the dropout, meaning that a 50mm chain line is about 5mm too far out.
So i want to fix this on my bike. shimano has you put in a 2.5mm spacer between the bb cup and the bb shell. can i move this spacer to the non-drive side to move my chainline in 2.5mm? anyone have any experience with this or any wisdom to add?