Bike Repair: Chain

3 things you need to know about that linked loop that keeps your wheels turning.

April 30, 2010

1. Don't stretch your luck

Your chain doesn't actually stretch. The holes in which the pins connect the individual links begin to ovalize over time and eventually change the tolerances of the chain. When this happens, the worn chain will begin to wear the teeth on your chainring and cassette. You'll know your drivetrain is worn when its teeth start to resemble shark fins (if you let it get this far, replace your cassette and chainrings along with the chain). To prevent this, keep track of your chain's wear and replace it before it has a chance to destroy your drivetrain. To measure, line up the first line on a 12-inch ruler with the center of a pin. The last line on the ruler should also fall in the center of a pin. If it measures 1*16 inch or longer, you need to replace your chain.



2. Wear the right size

For a smooth ride, it's essential to run the correct-width chain relative to your bike's drivetrain. Chain sizes are standard, and listed on the chain's packaging. To figure out a chain's size on your own, line up the jaws of a pair of calipers over the center of both ends of a chain pin. Five- or six-speed bikes need a chain with a diameter of 7.5 to 8mm; seven- and eight-speed bikes, 7 to 7.5mm; and nine-speed bikes, 6.5 to 6.9mm. The most commonly used chain, the 10-speed, needs a 5.9 to 6.1mm chain. Although SRAM and Shimano chains are, in some cases, interchangeable (Campagnolo is not), it's best to stick with the same brand for both your chain and your drivetrain, especially when you get into the nine- and 10-speed range.


3. Stop sucking up

You'll know when it happens. You're riding along and suddenly your pedals lock up and you're forced to stop abruptly. You've just experienced chain suck--when your chain doesn't disengage from the bottom teeth of the front chainring and instead gets caught up on the teeth and pulled back up the ring onto itself, jamming between the chainrings and chainstay. Common causes: a worn chain with stiff links, bent or damaged teeth on your chainring, mud or wet grit on your chain and cassette, misaligned chainline (how your chainrings line up with your cassette), or shifting late under pedaling load. If you don't figure out the cause and fix it, you run the risk of damaging your frame and drivetrain components.