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