A crankshaft pulley is a pulley which attaches directly to the
crankshaft, outside the engine block, where it drives the
serpentine belt. It is the component which transfers rotational
energy to components such as the alternator and water pump. Its
size, in relation to the size of all the other pulleys,
depermines the amount of the engine's power gets transferred to
the various components. A large crankshaft pulley with small
component pulleys will give the components a lot of power, and
less of the engine's power is sent to the drive wheels. However,
if the crankshaft pulley is too small or a component's pulley
too large, not enough power will be sent to the components.
Because of this, there needs to be a balance between power sent
to the components and power sent to the wheels. When production
cars are designed, there is usually a bit of bias towards the
components, because if there is just enough for the components,
there won't be enough as engine power is lost with age, or if
something is modified later.