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About Bicycle Chainline
Translations of this article (older version): German German flag
Sheldon Brown photo
by Sheldon "Straight Ahead" Brown
revised by John "What's Your Angle?" Allen
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Chainline

This is the lead article about chainline. Read it in connection with one of these other articles:

Chainline Illustration

The word "chainline" refers to how straight the chain runs between the front and rear sprockets. Ideally, both sprockets should be in the same plane, so that there is no sideward motion or stress to the chain. This constitutes "perfect chainline".

In the case of derailer geared bicycles, the chainline is not perfect in most gears. Chainline mismatch can cause the chain to rub against the side of an outer, larger chainring when engaged with a smaller one, and can cause problems with shifting, especially with the front derailer. The worse the chainline, the worse the mechanical efficiency of the drive train, though research has shown the loss to be minor, at least with modern, flexible chains.

"Correct" chainline for a derailer system is a matter of opinion, and depends on the intended use of the bicycle. There are two "simple" answers to the question of what constitutes proper chainline.

Chainline Standards:

Application Dimension Notes
Road Double 43.5 Shimano spec, measured to the midpoint between the rings.
with typical 5 mm chainring spacing, this puts the inner at 41 mm, the outer at 46 mm.
Road Triple 45 Shimano spec, measured to the middle ring.
MTB Triple 47.5-50 mm Shimano spec, measured to the middle ring.
47.5 preferred, but for frames with oversized seat tubes, the longer dimension may be needed, because the fat tube places the derailer mechanism farther to the right.
Track/Coaster Brake
Traditional One-Speed
Most internal gear hubs
40.5-42 mm Older bikes with 110 spacing would be on the smaller end of this range
Newer bikes with 120 mm spacing normally use 42 mm
Singlespeed MTB 52 mm Wider chainline need for chainstay clearance on MTBs.

This is close to the chainline of the outer ring of a typical MTB triple

Singlespeed MTB
Alternate
47.5 mm White Industries ENO hubs use this chainline, which lines up with the middle position of a typical MTB triple.
It's also fairly close to the outer position of a typical "road" double.
Rohloff Speedhub 54 mm
(58 mm w/13 tooth)
Freeride and Downhill 55 mm Newer Freeride and Downhill bikes with 150 mm spacing
 

Chainline Measurement-Front

Chainline is measured from the centerline of the frame to the center of the chain.

You can measure the front chainline directly with a simple ruler. Simply hold the ruler against the seat tube or down tube and measure the distance from the middle of the seat tube to the middle of the chainring teeth. In the case of triple chainwheel sets, measure to the middle chainring. In the case of doubles, measure to the halfway point between the two rings. In the photo below, the chainline is about 44 mm. It's easier to see the centerline of the seat tube than in this photo, because the reflection or shadow of the ruler curves away from where the ruler contacts the seat tube. (Or, if you know the diameter of the seat tube you can measure from the side nearest the chainwheel, and add half the seat tube's diameter.)

measuring chainline angle photo

Chainline Adjustment-Front

Front chainline may be adjusted either by moving chainwheels, or by moving the crank(s) -- also affecting tread, symmetry of the pedals around the bicycle's centerline, or both.

The list below covers all options, starting with the simpler ones.

Chainline Measurement-Rear

To measure rear chainline:

On a bicycle with a sprocket cluster, this is the chainline to the middle of the cluster. With a single chainwheel, this should match the front chainline, to equalize the chain angle for the inner and outer sprockets. With more than one chainwheel, the front chainline could be shifted a few mm inward or outward depending on how the chainwheels are to be used. The article about chainline with derailers covers that topic at length.

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Chainline Adjustment-Rear

More about rear chainline adjustment including data on specific hubs may be found in the articles:

Chainline may be adjusted at the rear wheel by rearranging spacers on the rear axle, and with a steel frame, also by re-spacing the rear dropouts. Adjustable hubs use conventional threaded axles, so you can increase the OLD spacing by removing the locknuts and adding spacer washers, and replace the axle as needed.

If you add equal thicknesses to both sides, the chainline is unaffected, since it's measured from the middle outward.

If you add more spacers to one side, or move them from one side to the other, you can change the chainline, but this will render a double-sided (flip-flop) hub unusable on one side or the other, since you'll be increasing the chainline on one side while decreasing it on the other -- unless you also use a different chainring depending on which way the wheel is inserted.

Moving spacers from one side to the other will disturb the alignment between a disc brake rotor and caliper. Re-spacing a frame will tilt the caliper and cause a slight lateral misalignment. Avoid these modifications unless the brake allows adjustments to compensate for them.

axel-set photo

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Thanks to John Dacey, Marten Gerritsen and Nilay Kothari for some of these data.

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