A chat with a frame builder totally changed how I see chainline

I was at a local bike show in Portland last weekend, just hanging out, and got talking to this older guy who builds custom steel frames. We were looking at a fixie with a wild chainline, and I made some comment about it being 'off'. He just smiled and said, 'Kid, you're thinking about it backwards. The chain doesn't care about the center of the frame, it cares about the straightest path between the two rings you're actually using.' He pulled out a ruler and showed me on his own bike, a 1x setup, how the chainring was deliberately offset to line up perfectly with the 5th cog out of 11 on the cassette. My mind was blown. I've been centering rings on the frame for years in the shop, never once thinking about the actual gear combinations people ride in. It makes so much sense now to set it up for the most used gears, not some abstract centerline. Has anyone else started setting up chainline this way for 1x or 2x systems?

3 comments

3 Comments

richarddixon7d ago

Why are we still using the old centerline rule at all? For a 1x, just pick your favorite gear and line up to that cog. For 2x, you have to split the difference, but maybe shift a tiny bit toward the small ring if that's what the rider lives in.

the_robert7d ago

Wait, you guys weren't already doing this? For a 1x, it's so obvious once you see it. You set it for the gear you spin all day. For 2x, you have to make a choice, but it's still about the ride, not the frame. That old centerline rule is just lazy building. My mind is still blown from reading this.

emma_rodriguez307d ago

Totally makes sense for 1x. For 2x it gets trickier since you're trying to split the difference between two rings. I still aim for the middle of the cassette but maybe shift it a mm or two based on the rider's big ring use.