My chain is stretched! I’ve heard it many times, as if the chain pulls out of shape, elongates and becomes longer. This is not what actually happens.
The major cause of chain "stretch" is wearing away of the metal where the link pin rotates inside of the roller. If you take apart an old, worn-out chain, you can easily see that the pin wear is evident, and if you was to compare and old roller to a new one, and measure the internal diameter, you would notice a difference.
Chain wear is something that you should check regularly. Excessively worn chains will cause faster wear to other components and lead to gears slipping and in extreme cases the chain snapping.
How do we measure chain wear?
The simplest and easiest way is to use one of the readily available tools for sale, which gives you a fairly accurate measurement to a percentage of wear. A chain wear gauge will read 0.5% wear through to .75%.
The latter measurement is when the chain needs to be replaced
A simple method of gauging wear is putting the chain on the outer chainring, then lift the chain off the chainring, if you see a visible tooth, then chances are it’s worn, however this is not the most accurate, only a rough visual guide.
For the technically minded, we can measure the distance between the pins. For this, have your tape measure to hand. 10 links of a new chain will measure 25,4 cm, if you measure between 25,4 and 25,5 cm, then all is good. If you can measure 25.7 cm, It will be time to replace the chain, sprockets and chainring, and possibly the pulley wheels.
So, how often should I check for wear?
Frequently people ask “how many miles can I expect out of a chain?” That is very difficult to answer this question, because chain wear depends on the usage, rider’s condition and degree of maintenance.
In general check your chain at the following intervals: Road use and riding in the dry: every 500 kilometres (310 miles). Off road use or more demanding environments: every 150 kilometres (93 miles) with a chain wear gauge tool.