Gravity affects a vehicle's handling by pulling it down.
When the weight of a vehicle is increased the friction force
is also increased. This same weight must also be accelerated
or slowed whenever you meneuver. If you are traveling up
a hill, gravity is trying to pull against your car. This
causes you to slow down.
When you're going
downhill, gravity pulls your car down, speeding you up.
When driving down a hill shift to a lower gear to reduce
speed. This will help prevent brake overheating, especially
for heavier vehicles such as trucks. The heavier your vehicle,
the more distance it takes to stop. If you double the weight
of your vehicle, it takes twice as long to stop.