How long should a chain last on a road bike?

Chain life varies all over the map, with the major wear factors being

• Your weight and style of riding. Heavier and/or stronger rider=greater chain wear. Kinda obvious. A 105 pound woman can get remarkably long chain life compared to a 240 pound guy. Nothing sexist here...you can reverse the numbers if you wish.
• A clean chain is a happy chain. Those who regularly keep their chains clean (not just the outside, but the interior bushings, where the real wear occurs) get much longer life than those who dont.
• Terrain. A BIG factor. My guess is that those who climb a lot probably get one-half the life out of a chain that someone in Nebraska gets.
• Chainstay length. Very short tri-bikes (those with 650c wheels) tear through chains very quickly. This is actually a function of two different things. First, the shorter chainstays mean the chain is frequently bending/twisting at a nastier angle than on a bike with longer chainstays. Second, the smaller wheels mean you have to use smaller rear cogs to achieve the same speed, and this accelerates both cog and chain wear.

All of these wear factors are cumulative, so its possible to wear a chain out *really* fast, or have one last *really* long, given the right (or wrong) mix of wear factors. I should also point out that mountain bikes can wear through chains in as little as 300 miles under "normal" use. This can occur even with regular cleaning, since a mountain bike chain gets so dirty so fast that it operates most of its life under less-than-ideal conditions! Obviously, the type of dirt you ride through has a major effect on the wear rate as well...kinda like how grittier sandpaper works a lot faster than fine sandpaper if you're trying to remove paint.

A typical 160 pound cyclist who rides a variety of terrain might get as little as 1500 miles or as much as 2500 (road cycling only). I get 2000 miles only if Ive been very good to my chain (which means I typically get only about 1500 before its excessively worn).

What are the dangers of riding with a worn-out chain?

The tooth pattern of your cogs and chainrings is fixed...meaning that they cannot match a stretched chain. What happens is that the stretched chain tries to wear them down to match their stretched shape, but the best the cog can do is have its profile rearranged, with the result that the parts that engage the chain are worn off. Eventually the chain begins to slip off the cogs under pressure, particularly on the smaller cogs.

The problem is that, even if you replace the chain before it actually skips, you have done enough wear to the cog profile that a brand new chain will skip on the rear! At this point, your only option is to replace the rear cassette. The front chainrings rarely get so bad that the chain can skip over them (although I have seen this happen), primarily because there are so many teeth trying to hold onto the chain.

Its my experience that a rear cassette (on a road bike) can last 20,000 miles if the chain is replaced regularly, and as little as 3,000 miles (maybe even less!) if used with a badly-worn chain. In fact, if you start with a badly-worn chain and put a new cassette on, it might only take a couple hundred miles to do it in.

What type of chain should I buy?

There are those who insist that more expensive chains don't last any longer than cheapie chains, and it's possible this is true. I do find, however, that the better chains typically exhibit much better shifting on the front (with very little noticeable difference on the rear