 
This position gives you the most control of
your bike. This is perfect for descending
or when riding in a nervous peloton. You are
closer to your brakes and also have the greatest
leverage in this position, and therefore more
stopping power.
This is the safest position to ride in, as
you can maintain a good grip at all times,
especially on uneven, potholed roads. This
is the most aggressive position on the bike.
With your hands lower, it pulls you forward
to be more aerodynamic. This low stance does
not always come naturally, so be prepared
to practice to get really comfortable and efficient.
Out of the saddle - hold the drops
when you are sprinting - it keeps you low
over the bike and in control, and in a really
powerful position as you haul on the bars.
Keep your elbows tucked in when you ride on
the drops. If you're thinking about aerodynamics
this is really important and crucially it
looks more pro, too.
 
This is the most common position to spend
the majority of your time on the bike. As
a starting point, make sure your brake hoods
are positioned correctly, at least horizontal
to the ground, sometimes pointing slightly
upwards and never, ever down. The hoods put
you slightly more upright than the drops,
which should make it more comfortable, but
you can also brake and change gear from this
position too. Do watch out though, as your
hands can slip off on uneven roads. It's also
not ideal for fast descending, as your centre
of gravity is not low enough, so cornering
fast is better from the drops. Because you're
more upright than the drops, it does create
more aerodynamic drag unless you really bend
your elbows and back. As a rough guide, expect
to be about 3km per hour slower for the same
effort when in this position. You want to
be holding the hoods when you are climbing
out the saddle. This is a really strong position
for climbing, and if you watch the pros, this
is what they will all be doing.
 
Holding your bar on the tops is great for
climbing long, steady climbs. It brings your
body up, opening your diaphragm and also tilting
your hips back, which makes it easier to recruit
your glute muscles for powerful, efficient
climbing. This upright position does make
it the least aerodynamic one available, creating
significantly more drag than both the drops and
the hoods. You should really use this
position only for climbing or riding slowly because
you are a long way from your brakes. Do not
ride like this in a bunch as you won't be
able to react in time and it is a bit irresponsible.
Never, ever ride out of the saddle like this,
simply because you look like an idiot.
So: drops for descending, control and aerodynamics,
hoods for all day comfort and climbing out
of the saddle, and tops for efficient climbing
in the saddle.
