Chain life varies all over the map, with the major wear factors
being:
#1: 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.
#2: 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 don't.
#3: 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.
#4: 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 it's 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.
In the SF Bay Area (our local region), 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 I've been very good to my chain (which means I typically
get only about 1500 before it's 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.
It's 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). --Mike--
