Dr. Diandra: The dirt on Bristol’s dirt tires


NASCAR teams must make minimal modifications to get their Next Gen cars ready to race on Bristol Motor Speedway’s dirt track. The primary changes are a stronger underbody, a diffuser modification, and mud flaps. Goodyear, on the other hand, had to produce a tire that looks and performs like no other tire you’ll see this season.

Racers call it ‘grip.’ Scientists call it friction. Whatever you call it, that force between tires and track is a prerequisite for a car to move, much less race.

A tire creates friction via its contact patch — the technical term for a tire’s footprint. Imagine lifting one corner of your car, putting a piece of paper on the ground, and then lowering the tire onto the paper. The imprint the tire leaves is its contact patch. That’s where friction happens. One reason racing slicks are wider than street-car tires is to create a bigger contact patch.

In addition to grip, friction creates heat. When you sand a piece of wood, both the sandpaper and the wood heat up. The same thing happens to a tire on a track. Tires must dissipate heat to prevent melting or blistering. That’s why the tread on a racing slick is only about 3/16 of an inch thick.

Like sandpaper wears wood, a track’s abrasiveness also wears the tire. Tires present an inherent trade-off: Soft tires grip, but wear quickly. Hard tires don’t wear as fast, but they also don’t grip as well.

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You can tell if a tire is designed for racing on dry pavement, wet pavement, or dirt just by looking at it.

A photo of a dirt tire (left), a slick (center) and a wet tire(right)
Photo by Mike Siberini/Goodyear

The racing slicks used at most events — the center tire in the photo above — are smooth. The lack of a tread pattern creates a big contact patch and maximizes heat dissipation.

Wet-weather tires (right) and dirt tires (left) sport tread patterns. The patterns are different because they serve different purposes.

Water or dirt between tire and track significantly decreases friction.

A wet-weather-tire’s grooves push water away from the tire. In the photo above, note how the channels all lead away from the tire’s center line. Pushing water away from the contact patch increases friction and thus speed. But wet-weather tires do limit a car: It can’t move so fast that the tire doesn’t have time to get water out of the way. If the tire is in contact with a thin layer of water rather than the track, the lack of friction causes the tire to slide instead of roll.

Before we go into how those big, chunky treads create grip, let’s look at how a normal racing slick works.

How tires produce friction

Friction is — to be blunt — weird. It’s such a complicated phenomenon that scientists still don’t completely understand it. But we understand the basics. Tires on asphalt (or concrete) produce friction mostly via the tire deforming around the surface, as I show below.

But there’s a second type of friction at work. Rubber molecules in the tire form atomic-level bonds with rubber on the track. While ‘interatomic bonds’ sounds fancy, it’s basically like you stepping on a wad of gum during a walk. The gum bonds to the bottom of your shoe, and then either your shoe pulls away from the gum/sidewalk, or the gum pulls away from the sidewalk and sticks to your shoe.

This adhesive type of friction creates the gobs of rubber that build up on a tire after a run. Drivers on old tires swerve before a restart partly to scrape off the rubber gunk and expose a clean surface that will provide better friction.

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A crew member burns debris off a tire during during the Ruoff Mortgage 500 at Phoenix Raceway on March 13, 2022 in Avondale, Arizona. (Photo by Sean Gardner/Getty Images)

Dirt tires do friction differently

Rubber creates pretty strong friction with asphalt and concrete. Dirt, however, is different story.

Dirt contains five components: minerals, living organisms, soil organic matter, gas and water. The particles in dirt come in sizes from smaller than a grain of sand to a couple of millimeters.

All dirt is not created equal. Loam — soil with particles of all sizes — is best for growing things. But if you want to race, you want clay. Clay soil is made up of small particles, densely packed with little or no air between them. The organic matter glues the soil particles tightly together. That’s why clay retains water better than other types of dirt.

Different types of clay produce different racing surfaces. Even though Bristol Motor Speedway is using the same dirt as last year, different preparation methods can lead to different surfaces.

Justin Haley ran an open modified car at the Bristol Dirt Nationals the week before the Richmond race. He noted approvingly that the track surface was “like glass” this year.

“They’ve got the preparation down to a science,” he said.

Smooth, slippery glass may not seem like an optimal racing surface, but it means that the surface is well packed and groomed. That, hopefully, translates to fewer problems with blinding clouds of dust on restarts.

And more friction.

The friction between rubber and dirt, even perfectly prepared dirt, is less than the friction between rubber and asphalt. The Bristol dirt tire’s tread compound is just about as hard as the compound in a Bristol asphalt tire, but the dirt-tire compound works better in damp conditions.

The key to dirt friction, however, is those big square blocks of rubber.

A dirt tire’s tread pattern does help push loose dirt away, like wet-weather tires do with water. But the sharp edges of a dirt tire’s tread bite into the surface, much like the edge of a snow ski or a soccer shoe’s cleats.

All of these friction mechanisms allowed cars to make about 20-second laps on dirt at Bristol last year. The 2021 lap times at pavement Bristol were around 17 seconds, but the banking of the pavement track (24-28 degrees) was higher than that of the dirt track (18-19 degrees last year).

Dirt-track worries

Multiple mechanisms for producing friction mean multiple types of tire wear. There’s the usual wear from friction with the track surface. Under some conditions, dirt can blister tires the same way pavement can. But the edges of the tread blocks also wear, which gives them less bite. A sharp hoe cuts into dirt much better than a dull hoe. It’s also possible to tear or break off parts of the blocks.

Crew chiefs and drivers also must keep up with the track, which is a different challenge with dirt. Dirt tracks can take rubber, making the tread compound even more important. Heat from the cars can dry out the dirt and create dust. The opposite problem can also occur: Cars compact the dirt, making it so hard and slick that the tread blocks can’t cut into it.

Although this is only the second Cup Series dirt race for crew chiefs and drivers, Goodyear has a long history of making dirt tires. Greg Stucker, Goodyear’s director of race tire sales, didn’t know off the top of his head exactly how long they’ve been dirt racing.

“But I’ve been working for Goodyear for 40 years,” he said, “and they were making dirt tires when I started.”

Drivers to watch in Clash at the Coliseum


The 2023 NASCAR season will begin with Sunday’s Clash at the Coliseum, the second race on a purpose-built track inside Los Angeles Memorial Coliseum.

Although a non-points race, last year’s Clash generated intense interest as NASCAR moved the event from its long-time home at Daytona International Speedway to Los Angeles. The race was rated a success and opened doors for the possibility of future races in stadium environments.

MORE: NASCAR Power Rankings: 10 historic moments in the Clash

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Year Two will find drivers competing on a familiar landscape but still with a track freshly paved. Last year’s racing surface was removed after the Clash.

Drivers to watch Sunday at Los Angeles:


Joey Logano

  • Points position: Finished 2022 as Cup champion
  • Last three races: Won at Phoenix, 6th at Martinsville, 18th at Homestead
  • Past at Clash: Won in 2022

Logano put bookends on 2022 by winning the first Clash at the Coliseum and the season’s final race at Phoenix to win the Cup championship. He’ll be among the favorites Sunday.

Ross Chastain

  • Points position: 2nd in 2022
  • Last three races: 3rd at Phoenix, 4th at Martinsville, 2nd at Homestead
  • Past at Clash: Did not qualify last year

Chastain was the breakout star of 2022, winning a pair of races and generally putting himself front and center across much of the year. Can he start 2023 on a big note? If so, he will have to do so without replicating his Hail Melon move at Martinsville after NASCAR outlawed the move Tuesday.

Kevin Harvick

  • Points position: 15th in 2022
  • Last three races: 5th at Phoenix, 16th at Martinsville, 8th at Homestead
  • Past at Clash: 10th in 2022

Sunday will begin the final roundup for Harvick, who has said this season will be his last as a full-time Cup driver. He is likely to come out of the gate with fire in his eyes.


Kyle Busch

  • Points position: 13th in 2022
  • Last three races: 7th at Phoenix, 29th at Martinsville, 9th at Homestead
  • Past at Clash: 2nd in 2022

Welcome to Kyle Busch’s Brave New World. After 15 seasons at Joe Gibbs Racing, he begins a new segment of his career with Richard Childress Racing. He led 64 laps at last year’s Clash but couldn’t catch Joey Logano at the end.

Tyler Reddick

  • Points position: 14th in 2022
  • Last three races: 23rd at Phoenix, 35th at Martinsville, 35th at Homestead
  • Past at Clash: 21st in 2022

Reddick ran surprisingly strong in last year’s Clash, leading 51 laps before parking with drivetrain issues. He starts the new year with a new ride — at 23XI Racing.

Ty Gibbs

  • Points position: Won Xfinity Series championship in 2022
  • Last three (Cup) races: 19th at Martinsville, 22nd at Homestead, 22nd at Las Vegas
  • Past at Clash: Did not compete in 2022

After a successful — and controversial — Xfinity season, Gibbs moves up to Cup full-time with his grandfather’s team. Will he be the brash young kid of 2022 or a steadier driver in Season One in Cup?







Interstate Batteries extends sponsorship with Joe Gibbs Racing


Interstate Batteries, which has been a Joe Gibbs Racing sponsor since the team’s first race, has expanded its involvement with the team for 2023.

Interstate, based in Dallas, will be a primary JGR sponsor for 13 races, up from six races, the number it typically sponsored each year since 2008.

Christopher Bell and Ty Gibbs will run the majority of Interstate’s sponsorship races, but Denny Hamlin and Martin Truex Jr. also will carry the sponsor colors.

MORE: NASCAR outlaws Ross Chastain Martinsville move

“We’re extremely proud of our partnership with our founding sponsor, Interstate Batteries,” said team owner Joe Gibbs in a statement released by the team. “They have been such an important part of our team for over three decades now, and it’s exciting to have them on board all four of our cars this season. The best part of our partnership is the relationships we’ve built with everyone there over the years.”

Bell will carry Interstate sponsorship in Sunday’s Clash at the Coliseum, the All-Star Race May 21, the Coca-Cola 600 May 28, at Texas Motor Speedway Sept. 24 and at Martinsville Oct. 29.

Gibbs, in his first full season in Cup racing, will be sponsored by Interstate at Daytona Feb. 19, Bristol April 9, Nashville June 25, Chicago July 2, Texas Sept. 24 and Charlotte Oct. 8.

Hamlin will ride with Interstate sponsorship March 26 at Circuit of the Americas, and Truex will be sponsored by Interstate July 23 at Pocono.

Interstate was a key JGR sponsor in the team’s first season in 1992.

NASCAR announces rule changes for 2023 season


CONCORD, N.C. — NASCAR announced a series of rule changes for the 2023 season that includes outlawing the move Ross Chastain made at Martinsville and eliminating stage breaks at all six Cup road course events.

NASCAR announced the changes in a session with reporters Tuesday at the NASCAR R&D Center.

Among new things for this season:

  • Updated penalty for a wheel coming off a car.
  • Change to the amount of time teams have to repair cars on pit road via the Damaged Vehicle Policy.
  • Change to playoff eligibility for drivers.
  • Cars could run in wet weather conditions on short ovals.
  • Expansion of the restart zone on a trial basis.
  • Choose rule will be in place for more races.

MORE: Ranking top 10 moments at the Clash

NASCAR updated its policy on a loose wheel. Previously, if a wheel came off a car during an event, it would be a four-race suspension for the crew chief and two pit crew members. That has changed this year.

If a wheel comes off a car while the vehicle is still on pit road, the vehicle restarts at the tail end of the field. If a wheel comes off a vehicle while it is on pit road under green-flag conditions, it is a pass-thru penalty.

The rule changes once a vehicle has left pit road and loses a wheel.

Any vehicle that loses a wheel on the track will be penalized two laps and have two pit crew members suspended for two races. The suspensions will go to those most responsible for the wheel coming off. This change takes away a suspension to the crew chief. The policy is the same for Cup, Xfinity and Trucks.

With some pit crew members working multiple series, the suspension is only for that series. So, if a pit crew member is suspended two races in the Xfinity Series for a wheel coming off, they can still work the Cup race the following day.

The Damaged Vehicle Policy clock will be 7 minutes this season. It had been six minutes last year and was increased to 10 minutes during the playoffs. After talking with teams, NASCAR has settled on seven minutes for teams to make repairs on pit road or be eliminated. Teams can replace toe links on pit road but not control arms. Teams also are not permitted to have specialized repair tools in the pits.

NASCAR will have a wet weather package for select oval tracks: the Clash at the Los Angeles Memorial Coliseum, Lucas Oil Raceway Park, Martinsville, Milwaukee, New Hampshire, North Wilkesboro, Phoenix and Richmond.

Elton Sawyer, senior vice president of competition for NASCAR, said that teams have been told to show up at these events prepared for wet weather conditions as they would at a road course. That includes having a windshield wiper. Wet weather tires will be available. 

“Our goal here is to get back to racing as soon as possible,” Swayer said. “… If there’s an opportunity for us to get some cars or trucks on the racetrack and speed up that (track-drying) process and we can get back to racing, that’s what our goal is. We don’t want to be racing in full-blown rain (at those tracks) and we’ve got spray like we would on a road course.”

NASCAR stated that it is removing the requirement that a winning driver be in the top 30 in points in Cup or top 20 in Xfinity or Trucks to become eligible for the playoffs. As long as a driver is competing full-time — or has a waiver for the races they missed, a win will make them playoff eligible.

With the consultation of drivers, NASCAR is expanding the restart zone to give the leader more room to take off. NASCAR said it will evaluate if to keep this in place after the Atlanta race in March.

NASCAR stated the choose rule will be in effect for superspeedways and dirt races.

NASCAR eliminates stage breaks for Cup road course events

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CONCORD, N.C. — NASCAR will do away with stage breaks in all six Cup road course races and select Xfinity and Truck races this season, but teams will continue to score stage points. 

NASCAR announced the change Tuesday in a session with reporters at the NASCAR R&D Center. 

MORE: NASCAR outlaws Ross Chastain Martinsville move

NASCAR stated there will be no stage breaks in the Cup road course events at Circuit of the Americas (March 26), Sonoma (June 11), Chicago street course (July 2), Indianapolis road course (Aug. 13), Watkins Glen (Aug. 20) and Charlotte Roval (Oct. 8).

There will be no stage breaks for Xfinity races at Circuit of the Americas (March 25), Sonoma (June 10), Chicago street course (July 1), Indianapolis road course (Aug. 12), Watkins Glen (Aug. 19) and Charlotte Roval (Oct. 7).

There will be no stage breaks for the Craftsman Truck Series race at Circuit of the Americas (March 25).

In those races, stage points will be awarded on a designated lap, but there will be no green-and-checkered flag and the racing will continue.

The only road course events that will have stage breaks will be Xfinity standalone races at Portland (June 3) and Road America (July 29) and the Truck standalone race at Mid-Ohio (July 8). Those events will keep stage breaks because they have non-live pit stops — where the field comes down pit road together and positions cannot be gained or lost provided the stop is completed in the prescribed time by NASCAR.

NASCAR has faced questions from fans and competitors about stage breaks during road course races because those breaks alter strategy in a more defined manner than on most ovals.

Elton Sawyer, senior vice president of competition for NASCAR, said the move away from stage breaks at road courses was made in collaboration with teams and response from fans.

“When we introduced stage racing … we took an element of strategy away from the event,” Sawyer. “Felt this (change) would bring some new storylines (in an event).”

NASCAR instituted stage breaks and stage points for the 2017 season and has kept the system in place since. NASCAR awards a playoff point to the stage winner along with 10 points. The top 10 at the end of a stage score points.

It wasn’t uncommon for many teams to elect to pit before the first stage in a road course race and eschew points to put themselves in better track position for the final two stages. By pitting early, they would be behind those who stayed out to collect the stage points. At the stage break, those who had yet to pit would do so, allowing those who stopped before the break to leapfrog back to the front.