Dr. Diandra: Explaining Ross Chastain’s Martinsville move


Ross Chastain provided a superb physics lesson at Martinsville. Here’s how he managed to pass five cars in the last half-lap of the race.

Turning requires turning force

Imagine swinging a tennis ball tied to a string above your head. The ball moves in a circle because of the string.

That string provides a force that makes the ball turn. This turning force always points toward the center of the turn. Physicists call it ‘centripetal force’, but I think ‘turning force’ is more descriptive.

Turning at a race track utilizes the exact same physical principle — except without the string.

And these 3,675-pound cars require a lot more turning force than a tennis ball does.

The amount of force necessary to turn is proportional to the mass that’s turning, times the speed, times the speed again, all divided by the turn radius.

Physics tells us that:

  • Faster turns require more turning force.
  • Making tighter turns (like Martinsville) requires more turning force.
  • Heavier cars need more turning force.

Let’s figure out how much force you normally need at Martinsville. The pole speed was 96.078 mph, but each car’s speed varied throughout a lap.

  • During practice, cars reached 114-119 mph on the straightaways.
  • Drivers entered the turns from 75-85 mph, depending on the driver and the age of their tires.
  • Most drivers slowed to around 60 mph before speeding up again to exit the turn.

Let’s say a driver takes Martinsville’s 202-foot-radius turns doing an average of 80 mph. That requires a turning force of 7,775 pounds.

The four tires must generate all of that almost four tons of turning force.

Sir Isaac Newton discovered that force is equal to mass times acceleration. Chastain is 5’9”. I’ll guestimate his weight at around 160 pounds. That makes the total weight of the car and driver 3,675 pounds.

Dividing the force by the mass, the acceleration of a car turning at 80 mph at Martinsville is normally about 2.1 Gs, where G is the acceleration due to Earth’s gravity.

Your head, which weighs around 10 pounds, would feel like it weighed 20 pounds when subjected to a 2G acceleration.

Compare that to astronauts on the Space Shuttle, who experienced about 3Gs during takeoff.

Ross Chastain’s turning model

On the final lap, Chastain needed to pass two cars. But none of the cars he needed to pass were close enough for him to get to them.

Chastain floored it going into Turn 3. Instead of relying on just the tires for turning force, Chastain used the wall to help him turn. That gave him enough turning force to turn a lot faster.

Chastain’s lap time on Lap 499 was 20.758 seconds. His lap time on lap 500 was 18.845 seconds. As my colleague Dustin Long noted, that’s the fastest lap ever by a stock car at Martinsville Speedway.

Chastain did the first half of the lap normally. It would take him about half the time of lap 499: 10.379 seconds.

That means he completed the last half of the lap in 8.466 seconds. He had to run an average of 112 mph from the midpoint of the backstretch to the start/finish line.

He didn’t run 112 mph the whole way. Let’s assume he entered the turn at 122 mph, which would be 37-47 mph faster than anyone else did. We’re talking about a turning force of 18,079 pounds, and an acceleration of almost 5Gs.

Isn’t 5Gs dangerous?

A human being can tolerate 5Gs for a short time. A 10-pound head would feel like it was 50 pounds under a 5 G acceleration. But that’s not the primary problem.

The human body is optimized for the 1 G acceleration the Earth’s mass provides. When your body accelerates faster, it has to work harder to circulate blood. Without sufficient blood flow, organs don’t get enough oxygen.

A warning sign of excessive G’s is losing peripheral vision and the ability to see colors. When the brain senses a lack of oxygen, it shuts down the least important functions first.

But if the high acceleration persists, the person who is accelerating eventually blacks out. Fighter pilots wear pressurized suits to ensure their circulation remains normal.

Much of what we know about how the human body tolerates high accelerations is thanks to Air Force Colonel John Stapp. He experimented on himself in the 1950s, surviving 25Gs  for a little over a second and a peak force of 46.2Gs.

Unfortunately, his experiments permanently damaged his vision. However he lived another 45 years, dying at age 89 in 1999.

Ross Chastain not only made it into the Championship Four, he provided a great answer for every student who asks their math and science teacher: When am I ever going to use this?

North Wilkesboro’s worn surface will prove challenging to drivers


NORTH WILKESBORO, N.C. — Three Cup drivers got their first chance to experience North Wilkesboro Speedway’s worn racing surface Tuesday and said tires will play a key role in the NASCAR All-Star Race there on May 21.

Chris Buescher, Austin Dillon and Tyler Reddick took part in a Goodyear tire test Tuesday. That test was to continue Wednesday.

The verdict was unanimous about how important tire wear will be.

“This place has got a lot of character to it,” Reddick said. “Not a lot of grip and it’s pretty unforgiving. It’s a really fun place.”

Dillon said: “If you use up your tire too early, you’re going to really be in trouble. You really got to try to make those four tires live.”

Buescher said: “The surface here was so worn out already that we expect to be all over the place. The speeds are fairly slow just because of the amount of grip here. It’s hard to get wide open until you’re straight.”

Reddick noted the drop in speed over a short run during Tuesday’s test. That will mean a lot of off-throttle time.

“I think we were seeing a second-and-a-half falloff or so over even 50 laps and that was kind of surprising for me we didn’t have more falloff,” he said. “But, one little miscue, misstep into Turn 1 or Turn 3, you lose a second sliding up out of the groove and losing control of your car.”

“That’s with no traffic. Maybe with more traffic and everything, the falloff will be more, but certainly we’re out of control from I’d say Lap 10 on. You have to really take care of your car. … It’s really hard 30-40 laps into a run to even get wide open.”

Chris Buescher runs laps during a Goodyear tire test at North Wilkesboro Speedway, while Austin Dillon is on pit road. (Photo: Dustin Long)

One thing that stood out to Dillon was how the facility looks.

While the .625-mile racing surface remains the same since Cup last raced there in 1996, most everything else has changed.

In some cases, it is fresh red paint applied to structures but other work has been more extensive, including repaving the infield and pit road, adding lights for night racing, adding SAFER barriers, the construction of new suites in Turn 4 and new stands along the backstretch.

“It’s cool to see how much they’ve done to the track, the suites, the stands that they’re putting in,” Dillon said. “To me, the work that is going in here, we’re not just coming for one race. We’re coming here for a while. I’m excited about that.”

Drivers to watch in NASCAR Cup race at COTA


Sunday’s NASCAR Cup Series race at Circuit of the Americas in Austin, Texas, has attracted an entry list that includes talent beyond that of the tour regulars.

Jordan Taylor, who is substituting in the Hendrick Motorsports No. 9 Chevrolet for injured Chase Elliott, brings a resume that includes 31 IMSA class wins, two 24 Hours of Daytona overall wins and two IMSA wins at COTA.

MORE: NBC Driver Rankings: Christopher Bell is No. 1

Jenson Button won the Formula One championship in 2009 and has five F1 starts at COTA. He is scheduled to be a driver for the NASCAR entry in this year’s 24 Hours of Le Mans.

Kimi Raikkonen, entered by Trackhouse Racing as part of its Project 91 program, won the 2007 F1 championship and has eight F1 starts at the Austin track.

They will draw attention at COTA this weekend, along with these other drivers to watch:


Brad Keselowski

  • Points position: 5th
  • Best seasonal finish: 2nd (Atlanta I)
  • Past at COTA: 19th and 14th in two career starts

Keselowski hasn’t been a star in road course racing, but his 2023 season has started well, and he figures to be in the mix at the front Sunday. He led the white-flag lap at Atlanta last Sunday before Joey Logano passed him for the win.

AJ Allmendinger

  • Points position: 17th
  • Best seasonal finish: 6th (Daytona 500)
  • Past at COTA: 5th and 33rd in two starts

The Dinger is a road course expert. Last year at COTA, he was involved in tight racing on the final lap with Ross Chastain and Alex Bowman before Chastain emerged with the victory.

Ross Chastain

  • Points position: 3rd
  • Best seasonal finish: 3rd (Auto Club)
  • Past at COTA: Two straight top fours, including a win

Chastain lifted Trackhouse Racing’s profile by scoring his — and the team’s — first Cup victory at COTA last season. He’s not shy about participating in the last-lap bumping and thumping that often mark road course races.


Chris Buescher

  • Points position: 13th
  • Best seasonal finish: 4th (Daytona 500)
  • Past at COTA: 13th and 21st in two starts

Buescher has never led a lap at COTA and is coming off a 35th-place finish at Atlanta after being swept up in a Lap 190 crash. Although he has shown the power to run near the front this year, he has four consecutive finishes of 13th or worse.

Alex Bowman

  • Points position: 20th
  • Best seasonal finish: 3rd (Las Vegas I)
  • Past at COTA: Two straight top 10s

Bowman’s four-race run of consistent excellence (finishes of fifth, eighth, third and ninth) ended at Atlanta as he came home 14th and failed to lead a lap. At COTA, he is one of only four drivers with top-10 finishes in both races.

William Byron

  • Points position: 28th
  • Best seasonal finish: 1st (Las Vegas I, Phoenix I)
  • Past at COTA: 11th and 12th in two starts

Involvement in an accident at Atlanta ended Byron’s two-race winning streak. He’ll be looking to lead a lap at COTA for the first time.



Three Reaume Brothers Racing team members suspended by NASCAR


Three members of the Reaume Brothers Racing No. 33 Craftsman Truck Series team have been suspended for three races by NASCAR after a piece of tungsten ballast came off their truck during last Saturday’s race at Atlanta Motor Speedway.

The suspensions were announced Tuesday.

Crew chief Gregory Rayl and crew members Matthew Crossman and Travis Armstrong were suspended because of the safety violation. Mason Massey is the team’s driver.

MORE: Xfinity driver Josh Williams suspended for one race

In a tweet following the announcement of the penalty, the team said it will not file an appeal. “The ballast became dislodged only after the left side ballast container had significant contact with the racing surface,” according to the statement. “We would like to be clear that there was no negligence on the part of RBR personnel.”

NASCAR also announced Tuesday that Truck Series owner/driver Cory Roper, who had been suspended indefinitely for violating the substance abuse policy, has been reinstated.

The Cup, Xfinity and Truck Series are scheduled to race this weekend at Circuit of the Americas.


Josh Williams suspended for one race after Atlanta infraction


NASCAR Xfinity Series driver Josh Williams has been suspended for one race because of his actions during last Saturday’s Xfinity race at Atlanta Motor Speedway.

Williams will be ineligible to participate in Saturday’s Xfinity race at Circuit of the Americas in Austin, Texas. He would be able to return for the April 1 race at Richmond, Virginia.

Williams was penalized for a “behavioral” infraction, specifically disobeying a NASCAR request.

In a tweet after the suspension was announced, Williams said: “I stand behind what I did and I don’t regret any decisions I made. I stand behind NASCAR for these decisions and will continue and always support them.” He said Alex Labbe will drive the team’s No. 92 car at Circuit of the Americas this weekend.

MORE: Three Reaume Brothers Racing team members suspended

NASCAR officials ordered Williams off the track during Saturday’s race after his car was involved in an accident. Debris falling from his car prompted a caution flag, leading NASCAR to order him to park.

Instead of going to the garage area, Williams parked his car at the start-finish line and walked to pit road.

Williams was escorted to the NASCAR hauler office at the track. He waited there until the conclusion of the race and then met with officials for about 20 minutes.

MORE: NBC Power Rankings: Christopher Bell rises to the top

Section 8.8.9.I of the Xfinity Series Rule Book states that with the Damaged Vehicle Policy, NASCAR can order a car off the track: “At the discretion of the Series Managing Director, if a damaged vehicle elects not to enter pit road on the first opportunity or if a damaged vehicle exits pit road before sufficient repairs had been made and thereafter causes or extends a caution (e.g. leaking fluid, debris, etc.), then said vehicle may incur a lap(s) or time penalty or may not be permitted to return to the Race.”

Williams later admitted he had violated a rule but said he was frustrated by the NASCAR decision.

“We all work really hard and to only run ‘X’ amount of laps and then to have something like a piece of Bear Bond and put us out of the race, it’s really frustrating,” Williams said after his meeting with series officials. “Small team. We work really hard. We’ve got to make our sponsors happy, right? It doesn’t do any good sitting in the garage. It is what it is. We’ll learn from it and move on.

“I told them I was a little bit frustrated,” Williams said of NASCAR’s call, “but it was in the rule book.”