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What is Chainline and how do I achieve the optimum setting?

Chainline refers to how straight the chain runs between the chainring and sprocket, a perfect setup involves a chainline between chainring and sprocket being on the same line. The further your chainline varies from the optimum setting for your equipment the more likely your equipment is to suffer mechanical problems and create creaking or ticking noises as your pedal.

Measuring Chainline - Front

To measure your chainline for the Chainring, measure the centre-line from the centre of the frame to the centre of the chain, as pictured (example 42mm)

Measuring Chainline


Measuring Chainline - Rear

To measure your chainline for the sprocket, measure the centre-line between the inside edge of the rear dropouts of your frame (for example 120mm), divide this figure in half (example 60mm) then measure the distance from the inside edge of the rear dropout (sprocket side) to the sprocket (example 18mm), then subtract the dropout centre line measurement halved (as above 60mm) from the dropout to sprocket measurement (as above 18mm) and you'll get the rear chainline measurement (example 42mm)

The Front and Rear Chainlines should be exactly the same, if not you need to get them to be as close as possible by using the following techniques.

Front Chainline Adjustment

The majority of Bottom Brackets currently available for sale are symmetrical (same length of axle either side of the Bottom Bracket) so the best way to adjust chainline is to ensure you have the compatible Bottom Bracket recommended by the Chainset manufacturer, for example using a Miche Primato BB with a Miche Primato Chainset. Alternatively if you replace the bottom bracket with a shorter or longer model you can adjust the chainline, for example one that is 4mm shorter will decrease the chainline by 2mm on drive side and 2mm on the non-drive side, replacing the BB with one that is 4mm bigger will increase the chainline etc.

Note - If you go this route to a narrower chainline, make sure that there won't be a clearance problem between the frame and the crank or chainring.

Top Tip - before considering replacing components due to chainline, check they are actually installed correctly, as a Bottom Bracket that is not tightened up correctly can cause chainline to vary, after all we are talking about tiny variations in measurement so one turn on the BB to tighten or loosen it can make all the difference.

Rear Chainline Adjustment

Most chainline issues can be solved by adjusting the front chainline as it is much easier to do this than adjust the rear chainline by adding or removing spacers from the rear wheels axle.