Traction friction concerns the ability
of a wheel or tire to start, stop, and not skid
sideways. Automobile tires have treads to improve their
traction and decrease the chances of a skid. The treads
are shaped differently for various weather conditions.
Race car tires normally don't have treads and use
adhesive properties of the rubber for their traction.
Questions you may have include:
How do treads help a car stop or
Why should tread design concern the
Why do race cars have wide tires?
Treads increase traction
With most vehicles, you want the rolling
friction to be at a minimum. But you also want to be
able to effectively start and stop without slipping, as
well as to prevent skidding when going around a corner.
For example, train wheels have very low rolling
friction, but they also have very poor traction when
starting or stopping.
Treads are added to automobile tires to
provide them with good traction. Although rubber
provides relatively good static and kinetic friction,
automobile tires have treads to further increase their
traction and to account for different weather and
driving conditions. The edges of the treads add to the
coefficient of friction when stopping or starting.
Tire treads give more traction, plus
help move water outward in wet conditions
Most of the treads on an automobile tire
are somewhat zigzagged. This increases the traction in
starting and stopping the car, plus this type of tread
also helps to prevent the car from skidding sideways
when it goes around a curve.
Treads for different weather conditions
Some tire treads are arranged to help in
wet conditions, as they channel excess water out from
under the tires. Snow tires have deeper, wider treads to
improve traction in the snow.
Some tires have wider treads to improve traction in snow or mud
When a tire becomes worn and the edges
of the treads become rounded, there can be considerably
less traction. The danger then is that the car may go
into a skid when going around a corner or may not be
able to stop in a sufficient distance in an emergency.
Tires on race cars usually have at the
most 1/8 inch of tread. The treads aren't really used
for traction as in a passenger car. Instead they help
dissipate heat, which is the major reason for tire
failure, particularly at the high speeds attained in the
race. Some tires may get so hot that the rubber blisters
and the tire blows out.
The aerodynamics of the race cars push
them downward the faster the car goes, adding to the
Treads aren't really needed in race car
driving since the cars tend to skid somewhat when going
around a curve. This is a controlled slide, as opposed
to an out-of-control skid in a passenger car. Also, race
cars don't get involved in the stop and go traffic of a
passenger car, so they don't need the treads for
starting and stopping.
Instead of standard tires, race cars use
rubber that is soft and almost sticky to the road. This
is a form of molecular friction, and it is related to
the surface area on the road. When a race car slides, it
is more controlled with this type of tire than with a
tire with treads, which may skid suddenly. The warmer
the tire gets, the better its traction. This is provided
the tire doesn't get so hot that it blisters.
Although race car tires have only 1/8
inch tread at most, drag-strip tires have no tread at
all. They don't need it, since there is no sideward
sliding and the race is not long enough to cause the
tires to overheat. But they do get plenty hot, as the
car spins its wheels. The type of tire used in drag
racing is often called a "slick" because of no tread.
Some race car tires are called "slicks" because they have no treads
The big disadvantage of having minimal
or no treads in race car tires is if there is rain, the
tires slip so much that it can be dangerous for the
drivers and their cars. The adhesiveness of the rubber
is lost when there is a layer of water between the tire
and the pavement. Most automobile races are called off
or delayed if there is rain.
Treads are added to tires to improve
their traction friction. This makes them more effective
in starting and stopped, as well as to help prevent
skids when going around a corner. Special tread
combinations also provide better traction in various
weather conditions. Race car tires use the stickiness of
soft rubber for their traction. This is good for
controlled slides but not good for wet surfaces.