This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.
One thing to decide before buying a bike is what type to buy. Here's a
Road bike Once known as a "ten-speed", most are now 12 or 14 (or even
16) speed. There are several sub-types: racing, sport,
and touring, the difference mostly in frame geometry.
ATB All-terrain bike, also known as mountain bike. Great for
riding in the dirt, these bikes usually have fat, knobby
tires for traction in dirt and gravel.
Hybrid A bike that borrows from road bikes and ATBs. For example,
they have the light frame and 700c wheels of road bikes and
fat knobby tires, triple cranks, wide-range derailleurs,
flat handlebars and cantilever brakes from mountain bikes.
Bike buying hints
When you're ready to buy a bike, you should first decide what you want
to use the bike for. Do you want to race? Do you want to pedal along
leisurely? Do you want to ride in the dirt?
Next, you should decide on a price range. Plan to spend at least
$350 for a decent quality bike.
Now find a good bike shop. Ask friends who bike. Ask us here on the
net. Chances are, someone here lives in your area and can recommend
Now that you are ready to look for a bike, visit the shop(s) you have
selected. Test ride several bikes in your price range. How does it
feel? Does it fit you? How does it shift? Does it have the features
you are looking for? How do the shop personnel treat you? Remember
that the shop gets the bike disassembled and has to spend a couple of
hours putting it together and adjusting things, so look for sloppy
work (If you see some, you may want to try another shop). You might
want to try a bike above your price range to see what the differences
are (ask the salesperson).
Ask lots of questions - pick the salesperson's brain. If you don't
ask questions, they may recommend a bike that's not quite right
for you. Ask about places to ride, clubs, how to take care of your
bike, warranties, etc. Good shops will have knowledgable people
who can answer your questions. Some shops have free or low-cost
classes on bike maintenance; go and learn about how to fix a flat,
adjust the brakes and derailleurs, overhaul your bike, etc.
Ask your questions here - there are lots of people here just waiting
for an excuse to post!
Make sure that the bike fits you. If you don't, you may find that
you'll be sore in places you never knew could be so sore. For road
bikes, you should be able to straddle the top tube with your feet flat
on the ground and still have about 1 inch of clearance. For mountain
bikes, give yourself at least 2-3 inches of clearance. You may need
a longer or shorter stem or cranks depending on your build - most
bikes are setup for "average" bodies. The bike shop can help you
with adjustments to the handlebars and seat.
Now that you've decided on a bike, you need some accessories. You
should consider buying
a frame pump
a tube repair kit
tire levers (plastic)
a pressure gauge
a seat pack (for repair kit, wallet, keys, etc)
a water bottle and cage
The shop can help you select these items and install them on your bike.