DIANDRA LESLIE-PELECKY: Drivers may have different preferences when it comes to how their cars handle.
But there's one thing they all want more of.
JOSH BROWNE: Drivers always want more grip.
JOHN PROBST: You get on the radio and say, go get me another bottle of grip, you know. The driver needs more grip.
BRIAN VICKERS: You can never get enough of grip. That's probably not a very specific, scientific term. But you want more grip.
MALE NARRATOR: The roar of the engines, the squeal of the tires, then the race to victory lane. It all says, NASCAR.
A race car is much more than steel, gas, rubber and speed. A race car is a science experiment on wheels.
STEVE LETARTE: If you ask the driver what grip is, it's a warm and fuzzy feeling when he makes the corner that he's not gonna
spin out or wreck. If you ask the crew chief what grip is, grip is a thing that's warm and fuzzy and makes him sleep at night,
knowing he has it. I'm a tire man from back in the day. So in my opinion, grip is very simple. Grip is the amount of force that tire
has to cling to the road.
DIANDRA LESLIE-PELECKY: How much frictional force, or grip, the tires generate, is determined by two things. How well the tires
stick to the track's surface, and how much force is pushing the tires against the track.
NICK HUGHES: The construction of the tire itself can actually create lateral force. And then finally the compound, the actual
rubber that comes in contact with the surface of the road provides grip through friction.
DIANDRA LESLIE-PELECKY: NASCAR requires all cars to use the same type of tire for each race. That means the only way to get
more grip is to push the tires against the track harder. And that's where downforce comes in.
PATRICK CANUPP: The downforce is a good thing for us because it provides additional grip. It basically acts to push the
car through the tires into the track.
STEVE LETARTE: Well people would be amazed at the load on a wheel on one of these cars. You could see three, four,
five-thousand pounds of vertical load on the right front tire.
DIANDRA LESLIE-PELECKY: You can get downforce in different ways.
BRIAN VICKERS: The two broadest terms would be mechanical or aerodynamic. And you know, and both of those are very
difficult to adjust during a race.
DIANDRA LESLIE-PELECKY: Mechanical downforce is the weight of the car pushing down on the tires. Making the car heavier
may increase its grip, but it also makes the car slower. Air passing over the car creates aerodynamic downforce, which pushes
the tires into the track just like the weight of the car does, but it doesn't add to the weight the engine has to accelerate.
PATRICK CANUPP: It's like having weight on the car, but not having weight to carry around. And so it's a good, free thing.
DIANDRA LESLIE-PELECKY: But how can air create grip? After all, it's just air. Air molecules are constantly moving.
The average air molecule travels more than 1,000 miles an hour. A single air molecule doesn't do much when it hits a car.
But as a car thunders around the track at 180 miles per hour, we're not talking about a few molecules hitting it.
We're talking about billions and billions of molecules. Air molecules hit the car from different directions,
but we're interested in the ones that push down. How hard they push down depends on how fast they're moving.
PATRICK CANUPP: There's a well known principle called the Bernoulli Principle that basically is a
result of the equations of motion.
DIANDRA LESLIE-PELECKY: Bernoulli's Principal tells us that slower moving air exerts more pressure. More pressure on a
given area means more force. Downforce is generated anywhere there's a surface for air molecules to push against. The whole body
of the car creates downforce, but most comes from the splitter in front, and the wing in the back.
PATRICK CANUPP: Well the splitter generates downforce basically with pressure difference. The splitter is essentially a
horizontal shelf that allows the high pressure to push down on the front of the car. At the same time under the car, the air is
rushing under the car and there's a low pressure that's developed under the splitter.
DIANDRA LESLIE-PELECKY: A splitter literally splits the air flow. The air molecules that hit the top of the splitter, slow
down and create a high pressure region above the splitter. The air molecules that go under the car move faster, and create a lower
pressure region. The net result is downforce. Teams can move the splitter in or out to change the amount of downforce. Now front
downforce give you front grip. But you need grip in the back, too.
PATRICK CANUPP: The rear wing is a different object on the car as far as generating downforce. With this wing you actually
have flow under the bottom of the wing and on the top surface of the wing.
DIANDRA LESLIE-PELECKY: Air flows more slowly over the top of the wing than under the bottom. Just like the splitter,
there's a higher pressure on top and a lower pressure on the bottom of the wing. And that's where the rear downforce comes from. Teams
are allowed to change the angle of the wing from zero to sixteen degrees. A bigger angle creates more rear downforce.
Many factors come into play during a race. But everything from grip to gas mileage all focus on
one thing. Getting to victory lane. You can't have speed without science. And that's why aerodynamicists are always working on
new ways to make the downforce be with their car.