Twenty-seven tracks host ticketed NASCAR Cup Series races in 2022. Only Nashville Superspeedway was designed with a concrete racing surface. Martinville installed concrete in the bends in 1976, while Bristol and Dover switched from asphalt to concrete in 1992 and 1995, respectively.
The 1.33-mile Nashville track is a D-shaped oval and the longest of the four concrete tracks. At 14 degrees of incline, it’s slightly steeper than Martinsville (12 degrees), but much less steep than Dover (24 degrees) or Bristol (24-28 degrees.) If you count half of Martinsville, the concrete represents 13% of NASCAR Surfaces in the Cup series. Dirt makes up 3.7%, leaving asphalt to make up the remaining 83.3%.
Concrete vs Asphalt
Both concrete and asphalt are composites: aggregates (also called “small pebbles”) bound together by a glue-like material called a binder. Concrete dates from the Roman Empire, while the first asphalt roads were not built until 1848. The nature of the binders explains the difference in time.
Concrete generally uses a binder of Portland cement, a mixture of limestone and clay. Asphalt uses bitumen, a black tarry substance derived from the heavier components of crude oil, as a binder. The binders determine the method of application. While the concrete is being poured and cured, the asphalt must be heated to high temperatures before it can be extruded and allowed to cool.
Because asphalt is more flexible than concrete, asphalt can be laid in long, continuous swaths. Concrete should be poured in sections to avoid damage from weather-induced expansion and contraction. The lines between the concrete sections also facilitate water drainage. This is necessary because concrete is less porous than asphalt.
The flexibility of asphalt means that it does not distribute loads. Asphalt experiences greater and more concentrated stresses than concrete. The figure below shows typical stress distributions (in red) for asphalt and concrete.
As you might guess – from this graph or your own personal experience with potholes, asphalt is more easily damaged than concrete. Asphalt simply cannot withstand the high forces of racing cars taking tight turns at high speeds.
Transport engineer Van Walling has compiled the fascinating (yet unpublished) compendium Oval Track Almanac. The three volumes document 45 years of extensive research on more than 1,000 leads in the United States and abroad.
Martinsville, Walling explained, turned to concrete because race cars damaged the asphalt on corners. Trucks can damage asphalt in freeway exit loops in the same way.
“Between the high temperature and the force of the vehicles,” Walling said, “the asphalt can be moved, creating a texture like a washboard.”
Whereas “hustle“, as the phenomenon is called, is annoying for an exit ramp, these bumps create real problems for racing cars. Lane operators have no choice but frequent resurfacing or rebuilding – or the switch to concrete.
This does not mean that concrete runways are impermeable. In 2004, Jeff Gordon lost a Martinsville race because of the concrete coming out of the track. In 2018, part of Dover loose concrete surface and damaged Jaime McMurray’s car. Debris from the impact shattered the windows of a crosswalk above the running surface. This episode prompted Dale Earnhardt Jr. at Tweeter that ‘asphalt is for racing. Concrete is for sidewalks.
Walling, who studied the original plans for Daytona International Speedway, said NASCAR founder Bill France Sr. wouldn’t necessarily agree.
“He wanted the corners of Daytona to be concrete,” Walling said. “The problem was the cost.”
Concrete requires a much larger initial investment, and France was already struggling to secure funding.
“He originally planned for a running surface of 60 feet,” Walling said, “but ended up settling for 40 feet.”
If France hadn’t found the money, Walling says, Daytona could have become a much flatter track. The initial cost is the reason almost all new tracks are built with asphalt, although maintenance is more expensive in the long run.
How concrete changes the race
The primary gripping mechanism on any circuit is the tire deforming around the aggregate. Concrete, by its nature, is smoother than asphalt. When NASCAR measured roughness of the runway surface in 2019, Martinsville, Dover and Bristol were the three smoothest tracks.
The second adhesion mechanism is the adhesive interaction between rubber molecules on the track and on the tire. Although Goodyear designs its tires to lay rubber down on concrete tracks, the rubber does not stay put.
“At high speeds,” said Goodyear racing director Greg Stucker, “the track will gradually turn black as the cars lay rubber on the concrete surface, then turn white again under the warning flag when the tires will pick up a lot of that rubber, so keeping pace with that transition is an important part of race strategy.”
A driver loses traction on a concrete track much faster than on asphalt. Drivers have already turned more in 2022 with the Next Gen car than in the whole of 2021. The accident rate is also on the rise.
Nashville’s concrete surface can pose a real challenge. Dover, the only race of 2022 on an all-concrete track so far, had 13 warnings. That’s almost double the number of cautions in each of the previous two races, and triple the number of each of the previous two.
A positive point is that concrete does not wear out as quickly as asphalt. Even though the car is new, the surface will not have changed much since last year. The tires are also familiar. Teams have used Nashville’s left tire three times (including at Dover) and the right side six times this year. They’ve even run the same left-right configuration twice: at Charlotte and at the Texas All-Star Race.
Black and white
Follow color counts.
The sun emits a spectrum of electromagnetic waves. The little band that we can see is what we call light. But the sun also provides infrared waves, like the heat lamps restaurants use to keep food warm. Its ultraviolet waves are why you should wear plenty of sunscreen on the trail.
Different colored surfaces interact differently with the waves of the sun.
We see objects because they reflect, emit and/or transmit light. A red car absorbs all wavelengths of light except those corresponding to red. Only red wavelengths reach our eyes.
White surfaces reflect most wavelengths of light. This is why you see concrete as white – white light is the sum of all colors of light. Black surfaces, on the other hand, absorb a lot of light. Because no light is reflected, you see black. The same thing happens with infrared waves, which cause black surfaces to heat up faster than white surfaces.
White tracks also reflect more light into drivers’ eyes. Drivers will need tinted visors for the local 4:00 p.m. (5:00 p.m. Eastern) departure, which will be broadcast on NBC.
The heat causes the bitumen in the asphalt to release oils that make the track more slippery. This does not happen with concrete.
The end result is that a concrete track doesn’t change as much during a race as an asphalt track. The Nashville Superspeedway should be easier for crew chiefs to follow, as temperature changes won’t alter the racing surface as much.
On the negative side, if a team misses the setup, there is a much lower chance that the track will come to them during the race.
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Dr. Diandra: The Hard Facts About Nashville Superspeedway originally appeared on NBCSports.com