Kettenlinie - ganz schön schräg

Chain line - quite slanted

Singlespeed and fixie riders may be familiar with the word chainline, but "multi-speed" riders may not be.
Anyone who has ever built a bike themselves might also have stumbled across the topic.

Short explanation: With the ideal chain line, the chain runs from the sprocket on the rear wheel to the chainring on the crank in a line, without any inclination.
This is usually measured via the distance from the center of the axle or hub to the center of the chainring or sprocket.
You can measure or simply follow the various manufacturer instructions.
On single-speed and fixed-gear bikes, the chain should run as straight as possible, as appropriate "single-speed chains" are usually used here. These are wider and less flexible, which is why "skew" leads to increased wear on the teeth and chain.
It was only with the advent of the 1-speed groupset, for example 1x11, that flexible chains were developed to enable the necessary skewing of the chain. With "older" gears with 2 or 3 chainrings, extreme skewing of the chain was still frowned upon, for the same reasons as with single-speed chains. With 1x12 gears, a “good” chain line can also be quite slanted. This is because the chains become thinner and more flexible the more sprockets have to fit on the cassette. Of course, the sprockets also become thinner accordingly. More sprockets have to fit on the freewheel, the distances have to be smaller and the chain has to be thinner in order to find space. The increase in flexibility also prevents excessive wear of the teeth or chain in the event of greater skew. For “old school” riders like me, extreme skew still takes some getting used to, especially since the somewhat annoying “chain noise” can also increase.

Which chain line is recommended and when depends on the gears, the manufacturer and the bike. Anyone who pays attention will notice that the chain line has continued to increase - in other words, the chain has moved further and further outwards. On the one hand, this has to do with the increase in tire width. Wider tires require more space in the frame and the chainstays need to extend further out. So that the chainring does not rub against the struts, it also has to move outwards - the chain line increases.
On the other hand, cassettes with more sprockets require a larger chain line so that the chain in the smaller sprockets does not jam on the neighboring sprocket.
If you still ride with a "front derailleur", i.e. use 2 or 3 chainrings at the front, you can avoid tilting by switching to a different chainring.
It should also be mentioned that, contrary to expectations, the middle of the cassette does not correspond to the recommended chain line. This is because the problem of “the chain tilting on the neighboring sprocket” only occurs in the larger gears (= smaller sprockets); the chain line runs a little further out.

Long story short: If you plan to replace the crank, bottom bracket or cassette, you should also pay attention to the chain line. Furthermore, the Q factor often increases with the chain line.

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