This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.
From: email@example.com (Keith Bontrager)
Handlebars are probably the one component that deserves the most
respect. Easton recommends a new bar every two years. I don;t recall
if they include an "if you race" preface. I'd say that's probably
about right. Same for our aluminum bars. Yearly would be good
on bars that have not been engineered for extended fatigue lives.
Of course, if you don;t race, if you have more than one bike, if
you are a smooth rider, if you like to do "skyshots" you need to
work this in to the estimate. Getting tougher, eh? Many people
could ride on the good quality bars into the next millenium without
a problem. How do you sort it out? I don't know.
Many parts (not bars or forks) will give you ample warning if you bother
to inspect your bike regularly. Clean it. Look at it. There
are "hot spots" all over the bike that deserve carefull attention.
Fork crown. Welds if a rigid fork, crown material if its a sus fork.
Steerer. Hard to look at, but once a year, especially if it's aluminum
or if you've crashed hard with a big front impact. Also if there are
noises from the front of the bike when you climb or sprint, or
if the bike starts handling funny. Be careful when you change lower
head set races so you don't gouge up the steerer at the bottom.
If you have an AHS stem/steerer look at the steerer at the point
where the stem and HS bearings meet. Critical!
Stem. All of the welds and the binder. Especially if you are
a 200lb sprint specialist.
Down tube/head tube joint of the frame - underneath.
Top tube/ head tube joint - same location.
Seat tube - near the BB shell and near the seat binder clamp slot.
BB spindle. Hard to look at, but once a year. Look near the tapers
where the crank fits on. This is the weak spot. If the crank
feels funny when you are pedaling (hard to describe the feeling)
or if it comes loose unexpectedly, look long and hard at the spindle.
Cartridge BBs that allow you to change the bearings should be
treated with some respect. You can keep fresh bearings in them
forever, guaranteeing that they'll be in service until the
Cranks. Check the right hand arm all around where the arm leaves
the spider. Also check the hub where the arm attaches to the
spindle - especially if the arm is machined from bar (CNC). The
section near the pedal threads was prone to failure on older
road cranks though I have not seen this on MTB cranks (yet!).
Look all over the arms on the light aftermarket cranks. Often.
Seat post. Pull it out and sight down the quill. Any ripples
or deformation around the area where the post is clamped in the
frame indicates a failure on the way. The clamps are too varied to
comment on. If you have to run the fasteners real tight to keep
the saddle from slipping you should put new, very high strength
fasteners in every year or so. The clamps can come loose from the
quill tube sometimes (ask me how I know). Grab the saddle and give it
Saddle. Rails near the seat post support pieces.
Rims. material around spoke holes can pull out, side walls can
wear through, side walls can fail due to extrusion defects. Some
of these are hard to see.
Frames around the dropouts (not a problem with newer frames as it
was with older campy forged drops). Chainstays near the CS bridge
and BB shell.
Hubs. Flanges can pull away from the hub body. Not a problem
in most cases unless the wheels are poorly built, you are running
radial spokes and ride real hard, have poorly designed aftermarket
hubs, or are very unlucky.
Many components will make a bit of noise or make the bike feel funny
before they go. Not all will. Respect this.