Bicycle Chain Length

When you buy a bicycle chain it typically comes with somewhere between 110 and 116 links, longer than necessary for most bicycles. Chain length must then be shortened and links removed to fit the size and number of sprockets and chainrings that make up your drivetrain so shifting is smooth in every gear position.

Bicycle Chain is Too Long?
The ultimate goal is to have enough length to fit on the two largest gears and through the rear derailleur, in case you accidentally shift into that position. But if the chain is too long it will flop when in the small-small combination. Sag between the rear cog and front chainring will be a clear indication of too long of a bicycle chain length.

Rear derailleurs have different capacities to absorb chain length as a function of their range of travel. If you are having difficulties in finding the right bicycle chain length for the gears you have, it may be that your derailleur is not matched to the size and number of gears that you are trying to accommodate. Your only answer maybe to limit the gears that you use with a slightly shorter chain than expected so that it meets your derailleurs capacity without too much slack on the small gear combinations.... or consider a derailleur upgrade.

Bicycle Chain is Too Short?
On the flip side, if the chain is too short, and you shift into the large-large combination you take the risk of sucking the rear derailleur into the sprocket and damaging both chain and cog. If the rear derailleur straightens out fully when on the large gear and chainring, you have a clear indication that the chain is too short.

So then the obvious question is how to you determine the right length?

Method #1: Use The Old Chain
Well the easiest, just assuming you already have a old chain to work from, might be to just lay the old chain on a table and use it as a measuring stick to fit the new one.. just make sure that you break the links in such a fashion that the fitting on one end of the chain meshes with the fitting at the other.

Method #2: Measure off the Largest Cog and Chainring.
Wrap your chain around the largest sprocket on the rear cassette and the largest front chainring. Bring the ends together on the front chainring until they can be just connected, then add one extra link to the length.

This includes one set of inner and one set of outer plates adding 1" to the overall measurement. (it is important to NOT run the chain through the rear derailleur if you are using this method for measurement)

Method #3: The Calculator?
If you are looking for a more sophisticated answer try this fellows bicycle chain length calculator:

http://www.epicidiot.com/sports/chain_length_calculator.htm#stretch calculator

He uses the length of your chainstay, the number of teeth on your biggest chainring and the number of teeth on your biggest rear cog in a mathematical calculation to determine the optimum bicycle chain length. But for me this is too complicated and besides I don't have a computer in my shop to access his formula when I need to do the math.


Bike Chains: Length, Width, What's Best to Buy etc.

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copyright Jan. 2007