Originally Posted by
daniell
I have an old mountain bike which has a triple crank. Being that the chainrings need to be replaced, I am considering a 1 X setup. Measuring from the middle chainring, the chainline is 55mm. How would I calculate the needed chainline for a 1 X setup?
Thanks
There's nothing to calculate. The correct chainline for a frame doesn't change, and it should be intuitive that a single chainring would be the same distance as the middle chainring on a triple. Changing the crankset often requires a different bottom bracket (spindle length) to achieve the correct chainline for the bike.
However, are you sure you're measuring correctly? A typical "old mountain bike" has a chainline of 47.5-50mm. What bicycle are we talking about, exactly? Has the bottom bracket and/or crankset ever been replaced? It's possible the wrong BB was previously installed, which resulted in an incorrect chainline for that bike. Here's a good reference.
All About Bicycle Chainline