Tires and Aero
Link back to the Brickyard Test
A tire guy for one of the teams organizes the team's Goodyear
tires for the test.
He measured the depth of the wear holes in the tread. The
numbers marked on the tread are the depth in thousands of an
inch, a little more than a sixteenth.
Tire labels allow traceability to specific batches of materials
and processing. The vertical number on the left edge of the label
is the spring rate of the tire (1419 in this photo) at some inflation
pressure, 23 psi I was told.
I hadn't seen these cars in about four years and was surprised
how the shapes have changed. This is Dave Blaney's Ford Taurus.
The shape of the front fenders around the wheel opening is
what caught my attention. The front fenders have a crease at
the top just above the wheel well. And the fender flares out
in front of the tire and then in at back of the wheel well.
This view shows the flare out at the front and the flare in
at the back of the wheel opening.
This view of the right side of Tony Raines' car shows less
But a look down the left side of that same car gives us a
good look at the flare out in front of the wheel opening and
the flare in at the back. And the same configuration for the
wheel opening at the rear tire.
Here's what's going on. The front air dam rides close to the
track surface in the corners causing a pressure drop under the
front of the car creating downforce. These flares at the wheel
wells enhance downforce by pumping air from the back of the air
dam out to the side of the car. The air near the surface of the
tire tends to move with the tire and wants to exit at the rear
of the fender cutout. The flare in front of the wheelwell causes
air flowing around the car to create a lower pressure under the
It looks to me like the left-side shapes are more aggressive
than on the right. You'd want more downforce on the left-front
corner to offset the right-to-left weight transfer in a corner.
Getting the inside tires to work on an oval is a challenge.
A few years ago, when NASCAR rules mandated a big rear deck-lid
spoiler, that device generated a lot of drag and downforce at
the rear of the car. The teams complained of push, understeer,
because there was no downforce at the front of the car to balance
that from the spoiler. Over a period of several years NASCAR
allowed the teams to develop body shapes at the front of the
car that generate more downforce.
Before these changes NASCAR Winston Cup cars generated about
500 lbs of downforce total. Due to the big deck-lid spoiler and
the changes at the front a good body now puts out 1,500 lbs of