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Setting correct Chainline using W3

I understand that the W3 measurement goes from the BB center to the large chainring; but why, when the CL value is actually derived from the center or middle of the two chainrings on the crank or from the single chainring when using 1x?


So as an example: I have a double crankset that has a CL of 45.5. There is 8mm spacing between the two chainrings. So then would I set W3 to 49.5?


What about with a 1x crankset that has the same CL of 45.5? Would W3 remain at 45.5?


I'm probably overthinking this, but I feel that having an actual CL value, either in place of or in addition to W3, would be much simpler to determine. 



Setting chainline

You can display chainline as described at: bikecad.ca/chainline. You are correct that W3 is the distance from the center of the BB to the center of the outermost chainring. If you are dealing with a single chainring, then W3 is equal to chainline. Otherwise, if you know the average chainline but do not know W3, then W3 can be calculated as you suggest above. For a triple crankset, W3 would be average chainline plus the distance between chainrings. If it is a double crankset, then W3 would be the average chainline plus half the distance between chainrings.

I will consider adding the optoin to define crankset position based on chainline in a future update.

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