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.

Ruoff Mortgage 500
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.”

Short-track ace Sam Ard shares Xfinity record with Noah Gragson


Former two-time Xfinity Series champion Sam Ard’s name returned to the forefront in the past week as Noah Gragson tied Ard’s series record for consecutive victories at four.

Although Ard has been nominated for the NASCAR Hall of Fame, his exploits generally aren’t well-known among many who follow the modern sport of stock car racing. He was on the Hall voting list for the 2023 class but was not elected.

In the 1970s and ’80s, Ard was a short-track master in the vein of stars like Jack Ingram, Harry Gant and Butch Lindley, drivers who could show up at virtually any half-mile track across the country and take home the trophy.

He won the NASCAR Late Model (now the Xfinity Series) championship in 1983 and 1984, scoring 18 wins across those two seasons. He put together four victories in a row late in the 1983 season, winning at South Boston, Virginia; Martinsville, Virginia; Rougemont, North Carolina and Charlotte.

Ard was so dominant in 1984 that he had wrapped up the seasonal championship with two races remaining. In 28 series starts that year, he had 24 top-five finishes and 26 top-10 runs. He won eight times.

In the next-to-last race of the 1984 season, at North Carolina Speedway in Rockingham, Ard suffered critical head injuries when his car slid in fluid from another vehicle and hit the track’s outside wall.

That crash effectively ended Ard’s career and impacted the rest of his life. Ard often talked of learning to walk again as part of his recovery. He said he would use a walker in a pile of sawdust in his backyard so that the landing would be softer when he fell.

Ard eventually was diagnosed with Alzheimer’s disease and Parkinson’s disease. In 2006, responding to Ard’s financial problems, drivers Kyle Busch, Kevin Harvick and Dale Earnhardt Jr., among others, launched a drive to raise funds for his family.

Ard, a native of Scranton, S.C., died in April 2017. He was 78.






Drivers to watch in Cup Series race at Talladega Superspeedway


The NASCAR Cup Series playoffs will reach a critical point Sunday in a 500-mile chase at treacherous Talladega Superspeedway.

The overriding factor in any race at Talladega, NASCAR’s biggest track, is the unknown. With cars running so fast and so close together, multi-car accidents are not only possible but expected, and it’s easy to become the innocent victim of someone else’s mistake.

MORE: NASCAR penalizes William Byron for spinning Denny Hamlin

The tension is doubled for the 12 playoff drivers. A bad finish at Talladega could open the door for a probable playoff exit at the end of the round Oct. 9 at the Charlotte Motor Speedway Roval.

The playoffs to date have seen four wins by non-playoff drivers, an unprecedented result. Tyler Reddick was the most recent to join that list with a win last Sunday at Texas Motor Speedway.

A look at drivers to watch at Talladega:


Denny Hamlin

  • Points position: 6th
  • Last three races: 10th at Texas, 9th at Bristol, 2nd at Kansas
  • Past at Talladega: 2 career wins

Although he hasn’t won, Hamlin has finished in the top 10 in all four playoff races. In the past six races at Talladega, he has four finishes of seventh or better. Now if he can just keep people from running into him…

William Byron

  • Points position: 3rd
  • Last three races: 7th at Texas, 3rd at Bristol, 6th at Kansas
  • Past at Talladega: Best career finish is a second

Byron stands alone as the only playoff driver who has been able to avoid major crashes and trouble in the pits, and he has finished in the top 10 in all four playoff races. After Tuesday’s penalty for his incident with Denny Hamlin at Texas, he sits below the cutline entering Sunday’s race.

Brad Keselowski

  • Points position: 24th
  • Last three races: 8th at Texas, 13th at Bristol, 25th at Kansas
  • Past at Talladega: 6 wins, the active leader

Even in trying times, Keselowski is a threat at Talladega, where he last won in April 2021 (his last Cup victory). He has led 268 laps there in the past 13 races.


Kyle Busch

  • Points position: 15th
  • Last three races: 36th at Texas, 34th at Bristol, 26th at Kansas
  • Past at Talladega: 1 career win, in 2008

Is Busch going to steadily disappear into the mist as he rides out the final weeks of his final year with Joe Gibbs Racing? His best finish in the past four races is 26th. On the positive side this week, he’s the only driver to finish in the top 10 in this year’s three races at Daytona and Talladega.

Chase Elliott

  • Points position: 8th
  • Last three races: 32nd at Texas, 2nd at Bristol, 11th at Kansas
  • Past at Talladega: 1 career win, in 2019

Can Elliott rebound from a fiery finish and a 32nd-place run at Texas? Playoff points give him some comfort, but a second career win at Talladega would be greatly appreciated in the Hendrick camp.

Martin Truex Jr.

  • Points position: 17th
  • Last three races: 31st at Texas, 36th at Bristol, 5th at Kansas
  • Past at Talladega: Best career finish is 5th

Will one of the sport’s most enduring mysteries continue at Talladega? In 70 career starts at Daytona and Talladega, Truex, a former champion and a smooth driver, has zero wins. At Talladega, he has only three top-five finishes in 35 starts.




NBC will broadcast final six NASCAR Cup Series playoff races


The final six races in the chase for the NASCAR Cup Series championship will be televised by NBC.

The races remaining on the schedule are at Talladega Superspeedway (Oct. 2), the Charlotte Motor Speedway Roval (Oct. 9), Las Vegas Motor Speedway (Oct. 16), Homestead-Miami Speedway (Oct. 23), Martinsville Speedway (Oct. 30) and Phoenix Raceway (Nov. 6).

NBC’s broadcasting team will be on hand Sunday for what is typically a seasonal highlight — a 500-mile race at Talladega Superspeedway. The next week the playoffs move on to Charlotte for a cutoff race. The lowest four drivers in the playoff point standings will be eliminated from championship competition.

The Round of 8 is scheduled at Las Vegas, Homestead and Martinsville, with the tiny Martinsville track serving as the final cutoff race. The four drivers who advance from Martinsville will race for the title at Phoenix Nov. 6.

The high drama of the Phoenix race, in which the championship will go to the highest finisher of the four competing drivers, will be carried by both NBC and Peacock.

Post-race commentary and analysis for all six remaining Cup races will be carried on Peacock.

Kyle Larson is the series defending champion. Joey Logano carries the point lead into Sunday’s race at Talladega.

NASCAR viewer’s guide for Talladega Superspeedway


After a messy Sunday at Texas Motor Speedway, the NASCAR Cup Series playoffs move on this weekend to another potentially messy spot — Talladega Superspeedway.

Home to the Big One — an almost certain multi-car crash, Talladega also occasionally produces unexpected winners, including Richard Brickhouse, James Hylton, Lennie Pond, Ron Bouchard and Brad Keselowski.

The mix of tight drafting, the Next Gen car and general playoff tension should make Sunday’s 500-mile run quite the adventure.

On Sunday at Texas, Tyler Reddick became the second driver (after Chase Elliott) to score three wins this season.

Joey Logano enters Talladega with the playoff point lead.

Playoff rookies roll on

The four drivers participating in the Cup playoffs for the first time remain factors approaching the second race in the second round.

Ross Chastain is second in the standings, 18 points above the cutline entering Talladega.

MORE: NBC NASCAR rankings put Denny Hamlin first

Daniel Suarez, Chastain’s Trackhouse Racing teammate, is seventh. He’s four points above the cutline.

Two other playoff rookies — Chase Briscoe and Austin Cindric — will start Talladega below the cutline. Briscoe is four points below the cutline. Cindric is 11 points below the cutline.

Looking for wins

Only six of the remaining 12 playoff drivers have won races at the two remaining tracks in the second round (Talladega and Charlotte Roval).

Among the six, Joey Logano has the best win record at Talladega, having finished first there in 2015, 2016 and 2018.

Other Talladega winners in the group: Ryan Blaney (two), Denny Hamlin (two), Chase Elliott (one), Ross Chastain (one).

The Charlotte Roval is relatively new, of course, but Chase Elliott already owns two wins there. Ryan Blaney and Kyle Larson also have won at the Roval.

An opening for Brad?

Few people who watched it will forget the first Cup Series victory scored by Brad Keselowski.

It occurred at this week’s tour stop — Talladega Superspeedway — in April 2009. Keselowski and Carl Edwards made contact approaching the finish line and notched the win, even as Edwards’ car flew into the frontstretch fence, spraying car parts into the grandstands.

Thirteen years later, Keselowski returns to NASCAR’s biggest track having recorded six Talladega wins. No other active drive has more than three.

Keselowski’s refurbished team — Roush Fenway Keselowski Racing — has new fire with Chris Buescher winning at Bristol and Keselowski winning the pole and finishing eighth at Texas.

RFK Racing has led 309 laps in the past two races, more than the team had led in the prior 105 races combined.

Although he hasn’t won a Cup race since scoring a victory in a Team Penske Ford in April 2021 at Talladega, Keselowski must be considered a threat Sunday.

Entry lists

Thirty-seven drivers, including Xfinity Series star Noah Gragson and reigning Xfinity champion Daniel Hemric, are entered for Sunday’s Cup race.

Talladega Cup entry list

The Xfinity entry list includes 41 drivers for 38 spots. Among those joining the series regulars are Trevor Bayne, Parker Kligerman, Timmy Hill and Jeffrey Earnhardt.

Talladega Xfinity entry list

Forty-one drivers are entered for Saturday’s Camping World Truck Series race. Included are Kaz Grala, Ryan Preece, Natalie Decker, Jennifer Jo Cobb and Parker Kligerman.

Talladega Truck entry list

This week’s schedule and forecast

(All times Eastern)

Friday, Sept. 30

Forecast: Partly cloudy. High of 77. (Weather note: There is the possibility that Hurricane Ian could impact the race weekend, depending on its path).

  • 3:30 – 5 p.m. — Truck Series qualifying
  • 5:30 – 7 p.m. — Xfinity Series qualifying (USA Network)

Saturday, Oct. 1

Forecast: Overcast with showers at times. Potential for heavy rainfall. High of 73. 60% chance of rain.

  • 10:30 a.m. – Noon — Cup Series qualifying (NBC Sports app, Motor Racing Network, Sirius XM NASCAR Radio)
  • 12:30 p.m. — Truck Series race (94 laps, 250 miles; FS1, Motor Racing Network, SiriusXM NASCAR Radio)
  • 4 p.m. — Xfinity Series race (113 laps, 300 miles; USA Network, Motor Racing Network, SiriusXM NASCAR Radio)

Sunday, Oct. 2

Forecast: Sun in the morning, increasing clouds in the afternoon. Slight chance of a shower. High of 74.

  • 2 p.m. — Cup Series race (188 laps, 500 miles; NBC, Motor Racing Network, SiriusXM NASCAR Radio)