Should you check your chain?

Bicycle chain links are a half inch long from rivet to rivet. When you measure a brand new chain with a ruler, the rivets should all line up exactly on the inch and half inch marks. With use, the chains “stretch” so that the rivets no longer line up over the length of a ruler.

Chains don’t really “stretch” — the insides of the chain wear with use, resulting in parts with more play and an elongation of a length of chain. You measure chain wear (or stretch) by lining the chain against a ruler. Because the links are exactly 1/2 inch long, the measure from rivet to rivet should be on 1/2 inch increments.

You can see in this photo that the top, older chain has about a 1/16″ of wear at one foot. The bottom chain is a brand new, unused 10 speed chain. Click on the photo to see large if you want.

It’s not necessary to remove the chain to measure it — just line a ruler up along a straight part of a chain and measure from the middle of a rivet. If you see more than about 1/16th inch of wear along a six inch segment of chain, it’s a good idea to replace the chain. There are also chain wear measuring tools where you pop the tool on the chain to quickly and easily determine if your chain is worn.

Why should I change the chain?

Chain wear is important mostly for bicycles with rear derailleurs. Excessive wear leads to poor shifting, and worn chains increases wear on your cogs which makes shifting even worse.

You can get away with a little more chain wear on your singlespeeds, fixed gear bikes and bikes with hub gears. First of all, you can use beefier — and less expensive — chains. Derailleur shifting performance is not an issue, so worn cog teeth aren’t too big of a deal. When the teeth start to get the shark fin look like on the cog below, though, it’s past time to replace your chain and cog.

Coming later: How to replace your chain.