Chains do not stretch. The holes that contain the pins elongate over time and the cumulative effect makes the chain longer.
Using a worn chain will wear out other components – cassette cogs, dérailleur and the chain ring – as they have fixed spacing which do not mesh as well with the longer stretched chain.
Some of the side effects of using a worn chain on your bike can be worn chain rings causing chain suck and the gears not shifting as well. In really bad cases there might actually be some physical damage.
Replacing a chain is much cheaper than replacing a chain ring set, cassette or dérailleur. These components should last up to 6 chain replacements according to some Industry experts, provided the chains are maintained well.
The durability of a chain is affected by riding style, weather conditions, lubrication and the quality of the component themselves.
Hence its difficult to change a chain on the basis of distance or time. The best way to check for chain wear is to check the length of the chain to figure out if the chain has actually stretched.
snap of chain pitch, by Jonathan Levy
Steps to check for chain stretch
- The distance between two pins on the chain (called the pitch of the link) should be half an inch (every chain follows this).
- A link pair (two adjoining chain links) should measure an inch
- 12 link pairs on a new unstretched chain measure 12 inches (304.8mm).
- To allow for manufacturing inaccuracies we leave a 0.5% tolerance so that gives us a + or – 1.5mm over 12 link pairs.
The easiest way to figure out chain stretch is to check the length of 12 link pairs on your bike, which should ideally measure anywhere between 303.3mm and 305.3mm