Chain Stretch 

Chains are a consumable part of the bicycle drivetrain. As you pile on the miles, your bike’s chain will wear out. The internal parts of the chain, the rivets and rollers, begin to wear out and give the illusion of stretching. This wear can cause the chain to mesh poorly with cogs and chainrings, causing poor shifting, premature wear to the cogs and even skipping over the cogs. Since it’s far more expensive to replace your cassette than it is to replace a chain, knowing when to replace your chain can save you some money in the long run.

This Unior chain wear tool allows you to accurately determine when you should replace the chain.

How to use the Unior chain wear tool