Measuring Chain Wear

Chains do not really stretch, but their pins and rollers wear, and the gaps grow until the chain starts chewing the rear sprockets. Catch it in time and you replace a chain; leave it and you are buying a cassette as well, and often chainrings. A simple wear gauge drops into the chain and gives a clear answer in seconds. Most chain makers suggest replacing at 0.75% wear for 5 to 10-speed chains and at 0.5% for 11 and 12-speed ones, so know which your bike has. Some newer chains, such as SRAM's Flattop, need a gauge made for them. Check every few hundred miles, and always when shifting turns vague or the chain skips under load. It is the cheapest money-saving habit on this list.