I am trying to understand why shimano quotes a chainline value for chainsets. I always thought that the chainline value of the chainset on a bike with disc brakes would be dictated by that of the rear axle and cassette. Eg, you adjust the chainset in/out from the centre of the BB shell according to the calculated value of the middle sprocket from the imaginary centre line of the frame?
Yes, where the chain ring sits is determined by the rear hub spacing. Some companies (like Sram) just have one crank to cover 135mm QR, 142, 148 etc and have rings with different offsets to match where the cassette sits. For whatever reason, Shimano have the crank arms doing that, and all the rings are the same.
Yes, where the chain ring sits is determined by the rear hub spacing. Some companies (like Sram) just have one crank to cover 135mm QR, 142, 148 etc and have rings with different offsets to match where the cassette sits. For whatever reason, Shimano have the crank arms doing that, and all the rings are the same.
I would expect the c/set to be the same regardless and you instead adjust the position of the rings using spacers on the c/set axle or by putting spacers between the bb shell and the frame. That will adjust the chainline.
I would expect the c/set to be the same regardless and you instead adjust the position of the rings using spacers on the c/set axle or by putting spacers between the bb shell and the frame. That will adjust the chainline.
No It won't, because then your cranks will be asymmetric. At best you might get knee pain, at worst the crank arms will clash with the chainstays. You might get away with neither, but it's not optimal.
Back in the days of separate BBs you bought a BB with a longer axle that moved them out evenly. These days as Walleater mentioned above you just buy the correct Shimano chainset, or in other cases it's a universal crankset but with the correct specific offset of chainring for the bike.
N.b. there are niche cases (some specialized and some cannondales and probably others) where a bigger offset chainline is used to better center the rear hub flanges.
N.b.b. It's not the center of the cassette. Can't remember which way it's supposed to be but it's offset slightly, hence singlespeed kits have two different sized spacers.
Chain line is the distance from the centre of the frame to centre of the chain ring. It varies between say road, mtb and boost. It's not something that a home mechanic or bike shop mechanic chooses.
