Rockbros / Lexon carbon cranks gravel chainline

[LazyCyclist]

Hey there! I recently upgraded my gravel bike to a 1x12 GRX setup.

I have a spare set of carbon cranks from my road bike that I’d like to install and use with the GRX drivetrain. However, I’m getting confused about chainline and chainring offset.

The seller told me I need a 3 mm offset chainring, but wouldn’t that make the actual chainline around 44.5 mm (or even 44.5 - 3 = 41)? For GRX, wouldn’t it be better to use a 0 mm offset chainring?

Am I understanding this correctly?

[hubba]

You need to move the chainline to the other way so it becomes 47.5mm which would be good even less is ok. I think GRX 1x chainline is too wide being 49.7mm. So look for a chainring with the offset to the right direction if the chainring is not flippable.

You could also use spacers on the spindle to move the right crank a bit more right and then add a pedal washer to the left side then you can use 0mm offset chainring.

[Asco]

For most cranksets, the specified chainline is in between the rings in a 2x setup. That means if you mount a 1x chainring in the big ring position, it needs to be offset 3mm to get intended chainline.

Whether that chainline is what you need is a different question. It's possible that you need a 0 offset for the chainring to clear the chainstays, but not necessarily.

[Leo.D]

The key to this is understanding that chainring offset and chainline move in opposite directions — an offset ring pushes the chainring toward the frame.