Bicycle Chain Sizes

Determining chain sizes is a function of learning how to measure a bicycle chain width, both internal and external, and the bicycle chain pitch. These three elements together describe a bicycle chain size and give you the information you need to buy a new one.

bicycle chain width 1. How to measure bicycle chain width? INTERNAL
There are 1/8" (3.175mm) and 3/32" (2.38mm) width bicycle chain. Sizes refer to the distance between the two inner plates. (I-W)

This is often referred to as the bicycle chain tooth size, since it predetermines the size or thickness of the teeth on the cogs or chainrings that can fit within the rollers and plates of the chain and engage the power train.

Older one and three speed bikes use the thicker 1/8" chains. Thinner 3/32" chains are used on derailleur "6 speed and up" bicycles. Chain tooth size then is directly related to the internal width of the chain and that dictates the thickness of gears which in turn is specific to the type of bike.

2. How to Measure The EXTERNAL Bicycle Chain Width?
The external width of a bicycle chain (E-W) is the maximum width of the chain measuring on the outer edges of the outer plates or pins, whichever sticks out the most. It becomes critical the more gears you have in place on the rear cassette.

More gears means less space between the individual sprockets and thus less clearance for the chain. Bicycle sizes thus must reflect increasing numbers of gears by reducing the overall width of the chain without affecting the standard 3/32" internal measurement. Manufacturing innovations like flush mounted rivets and KMC's bushingless chains have offered solutions in creating a narrower chain.

Chain manufacturers typically use the number of gears as the way to differentiate chains for a 10 speed bike versus a thicker chain for a 9 speed bicycle. You'll commonly see "10s" or "9s" in the listings rather than referring to the actual measured external width, although often this information is available as well.

3. Bicycle Chain Pitch
For a complete conversation about bicycle chain sizes, you also need to consider the measurement that dictates the distance between adjoining pins or rivets.

For all purposes, you can consider it a given. All chains produced today are built with pins machined 1/2" apart. You may want to read a further discussion on "chain stretch" when you place a metal ruler against an old chain and find that the pins don't line up nicely at the 1/2" marks.. a clear sign that maybe it needs to be replaced.


More to Buying A Chain Than The Width:
Note that although there is a standard bicycle chain tooth size, both in width and pitch, that is not true in the actual shape of the gear teeth. Each manufacture designs the tooth shape on their sprockets slightly differently so finding compatible bicycle chain-gear-derailleur combinations is an important consideration before you buy a new chain.

So after all that, to define a bicycle chain size you need:

  1. Chain Internal Width: 3/32" for derailleur bikes
  2. Chain External Width: ie. 10s
  3. Chain Pitch: Typically 1/2"
  4. Sprocket Shape: Shimano vs SRAM

Bicycle Chains: What's Best to Buy etc.

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copyright Jan. 2007