Dr. Diandra: How teams race the same NASCAR Cup car at different tracks

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After winning last week, Ross Chastain‘s crew chief Phil Surgen noted that the car sitting in Talladega’s Victory Lane was the same car they’d won with at COTA.

“Really comes down to just the whole Next Gen platform,” Surgen said. “All the cars are the same, have the same range of adjustments, same group of parts. All the cars right now are essentially universal. We took that car after it was done at COTA, cleaned it up, set it up a little bit differently to come here.”

It turns out “cleaning up” a Next Gen car and setting it up “a little bit differently” is a major undertaking. So much of one that you may question whether it’s even fair to call it “the same car.”

Next Gen anatomy

Think of a car’s chassis as its skeleton. Before the Next Gen car, teams made their own chassis by welding steel tubing to NASCAR’s specifications. Now teams buy already welded chassis pieces and bolt them together. The change is similar to making a bespoke bookcase versus buying one from IKEA. While your sturdy, made-from-scratch furniture will never change, you can disassemble and re-assemble the IKEA bookcase. Of course NASCAR has tech inspections and IKEA doesn’t.

 

A graphic showing the five parts of the Next Gen chassis.
Graphic credit: NASCAR Rule Book

The main portion of the chassis comes in three pieces, as shown in the diagram above. The center section protects the driver from impacts, heat, flames and fumes. The front sub-frame assembly supports the engine and front suspension (among other things), and the rear sub-frame assembly does the same for the fuel cell and rear suspension.

Everything on the car, from suspension to body panels, attaches to the chassis. That means every aspect of the assembled car depends on precise chassis assembly.

A tolerance for units

NASCAR fabricators (and inspectors) talk in thousandths of inches. Sometimes, instead of saying ‘thousandths’, they say ‘thou’. This confuses people because most of us think ‘thou’ is thousands instead of thousandths. A thousand is 1,000 and a thousandth is 0.001. When I learned machining in graduate school, we called one one-thousandth of an inch a mil. You’ve likely seen that unit before on trash-bag boxes. A typical kitchen trash bag is a little less than a mil thick. A good outdoor trash bag is about three mils.

But since NASCAR sticks with thousandths, so will I.

To give you an idea of the sizes we’re discussing, here’s a photo of a ruler onto which I’ve superposed some values.

A photo of a ruler, with units shown in mils

 

As the graphic shows, 250 thousandths is 1/4 inch, 125 thousandths is 1/8 inch, and 0.160 inches is a little over 5/32 of an inch.

Why did I pick 0.160 thousandths?

Because that’s the maximum value of a little-talked-about part used in connecting chassis pieces. A part that gives teams the ability to introduce small amounts of asymmetry into the car.

Shimming

Shims are pieces of material typically used as fillers and spacers. You’ve probably seen packs of wedge-shaped wood shims in the home improvement store. They taper from just about nothing to a quarter inch. You break off the size you need. Those shims are good for things like leveling cabinets against an uneven floor or wall.

Precision shims, such as those used in manufacturing, can be made of any material and often come in increments of one one-thousandth of an inch (0.001″).

NASCAR allows teams to put shims of up to 160 thousandths of an inch between the main section and each of the sub-assemblies. In the diagram below, the shims are in red, the bolts used to attach them to the front sub-assembly are in dark blue, and the nuts are orange.

A graphic showing the shim placement between the center and front sub-assembly sections
Graphic credit: NASCAR Rule Book

Teams aren’t required to make all four shims the same thickness — or even to use shims on all four attachment points. Using different combinations of shims, they can shift the front and rear of the car slightly up, down, right or left. Because everything attaches to the chassis, those shifts ultimately affect everything from the suspension to the aerodynamics. The shim itself isn’t very big, but making that little of a shift at the join with the center section produces a larger shift by the time you get to the front or rear end of the car.

Cleaning up

When a car returns from the track, most teams remove everything from the door tops down. They remove the wrap and unbolt each composite body panel. They remove the engine, fuel cell, suspension, transaxle, hoses… even the windows.

Teams keep detailed notes on each car part. They know where, when and how long each piece was used. The team retires parts at the end of their reliable lifetimes. They clean and examine parts that can be re-used.

If the car will run at a track similar to the track it came from, the front and rear sub-assemblies might be left in place — especially if the car performed well. More often than not, though, the front and rear sub-assemblies come off, too.

Setting up the car “a little differently”

Teams reattach the same or different front and rear sub-assemblies with shimming specific to the track at which that car will race next. Chassis positioning determines suspension geometry, which affects everything from skew to travel. Different tracks call for different springs and shocks, different gear ratios, and sometimes, even different side windows. Teams replace body panels, then re-wrap the car in the sponsor’s colors.

This is not a fast process.

“It would be really difficult to turn (a car) around every week,” Surgen said. “Every third or fourth week, with the cleanup and the prep time that goes into it, you could use it every third or fourth week pretty easily.”

What about tech?

NASCAR’s Next Gen chassis design gives teams a fair amount of adjustment space. But how much does that matter given that each car must pass the Optical Screening System (OSS) in tech inspection?

According to the NASCAR rule book, the OSS allows +/-150 thousandths tolerance on body panels. If a measurement is specified at 3.000 inches, the car passes if the measurement is between 2.850 inches and 3.150 inches. That gives the team just short of a third of an inch from minimum to maximum value.

The OSS allows tolerances of +/-200 thousandths on the windshields. Teams get 0.4 inches of leeway there. As we saw last week, they attempt to use every last thousandth they can.

Is it the same car?

When a team talks about bringing ‘the same car’, that might mean only that they’re using the same center section, or even the same three main chassis sections. But most everything else on the car could be entirely different from what was on it at the last race.

Some people have suggested that the interchangeability of car parts means that anyone can put together a Next Gen car. That’s a huge oversimplification. There is a still a box within teams must work. Putting together a car requires high precision tools, experience and lots of knowledge to ensure the car provides the biggest advantage possible, but still passes inspection.

Drivers for Drive for Diversity combine revealed

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The 13 drivers who will participate in the Advance Auto Part Drive for Diversity Combine were revealed Thursday and range in age from 13-19.

The NASCAR Drive for Diversity Development Program was created in 2004 to develop and train ethnically diverse and female drivers both on and off the track. Cup drivers Bubba Wallace, Daniel Suarez and Kyle Larson came through the program.

The 2020 and 2021 combines were canceled due to the impact of COVID-19.

“We are thrilled that we are in a position to return to an in-person evaluation for this year’s Advance Auto Parts Drive for Diversity Combine,” Rev Racing CEO Max Seigel said in a statement. “We are energized by the high-level of participating athletes and look forward to building the best driver class for 2023. As an organization, we have never been more positioned for success and future growth.”

The youngest drivers are Quinn Davis and Nathan Lyons, who are both 13 years old.

The group includes 17-year-old Andrés Pérez de Lara, who finished seventh in his ARCA Menards Series debut in the Sept. 15 race at Bristol Motor Speedway.

Also among those invited to the combine is 15-year old Katie Hettinger, who will make her ARCA Menards Series West debut Oct.. 14 at the Las Vegas Bullring. She’s also scheduled to compete in the ARCA West season finale Nov. 4 at Phoenix Raceway.

 

 

Name

Age Hometown
Justin Campbell 17 Griffin, Georgia
Quinn Davis 13 Sparta, Tennessee
Eloy Sebastián

López Falcón

17 Mexico City, Mexico
Katie Hettinger 15 Dryden, MI
Caleb Johnson 15 Denver, CO
Nathan Lyons 13 Concord, NC
Andrés Pérez de Lara 17 Mexico City, Mexico
Jaiden Reyna 16 Cornelius, NC
Jordon Riddick 17 Sellersburg, IN
Paige Rogers 19 New Haven, IN
Lavar Scott 19 Carney’s Point, NJ
Regina Sirvent 19 Mexico City, Mexico
Lucas Vera 15 Charlotte, NC

 

Dr. Diandra: Crashes: Causes and complications

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Two drivers have missed races this year after hard rear-end crashes. Kurt Busch has been out since an incident in qualifying at Pocono in July. Alex Bowman backed hard into a wall at Texas and will miss Sunday’s race at the Charlotte Roval (2 p.m. ET, NBC).

Other drivers have noted that the hits they’ve taken in the Next Gen car are among the hardest they’ve felt in a Cup car.

“When I crashed it (at Auto Club Speedway in practice), I thought the car was destroyed, and it barely backed the bumper off. It just felt like somebody hit you with a hammer,” Kevin Harvick told NBC Sports.

The three most crucial parameters in determining the severity of a crash are:

  • How much kinetic energy the car carries
  • How long the collision takes
  • The angle at which the car hits

Angle

The last of these factors requires trigonometry to explain properly. You can probably intuit, however, that a shallower hit is preferable to a head-on — or rear-on — hit.

A graphic show shallower (low-angle) hits and deeper (high-angle) hits
Click for a larger view

When the angle between the car and the wall is small, most of the driver’s momentum starts and remains in the direction parallel to the wall. The car experiences a small change in velocity.

The larger the angle, the larger the change in perpendicular speed and the more force experienced. NASCAR has noted that more crashes this season have had greater angles than in the past.

Busch and Bowman both had pretty large-angle hits, so we’ll skip the trig.

Energy — in pounds of TNT

A car’s kinetic energy depends on how much it weighs and how fast it’s going. But the relationship between kinetic energy and speed is not linear: It’s quadratic. That means going twice as fast gives you four times more kinetic energy.

The graph shows the kinetic energies of different kinds of race cars at different speeds. To give you an idea of how much energy we’re talking about, I expressed the kinetic energy in terms of equivalent pounds of TNT.

A vertical bar graph showing kinetic energies for different types of racecars and their energies

  • A Next Gen car going 180 mph has the same kinetic energy as is stored in almost three pounds of TNT.
  • Because IndyCars are about half the weight of NASCAR’s Next Gen car, an IndyCar has about half the kinetic energy of a Next Gen car when both travel at the same speed.
  • At 330 mph, Top Fuel drag racers carry the equivalent of six pounds of TNT in kinetic energy.

All of a car’s kinetic energy must be transformed to other types of energy when the car slows or stops. NASCAR states that more crashes are occurring at higher closing speeds, which means more kinetic energy.

Longer collisions > shorter collisions

That seems counterintuitive, doesn’t it? Who wants to be in a crash any longer than necessary?

But the longer a collision takes, the more time there is to transform kinetic energy.

A pitting car starts slowing down well below it reaches its pit box. The car’s kinetic energy is transformed into heat energy (brakes and rotors warming), light energy (glowing rotors), and even sound energy (tires squealing).

The same amount of kinetic energy must be transformed in a collision — but much faster. In addition to heat, light and sound, energy is transformed via the car spinning and parts deforming or breaking. (This video about Michael McDowell’s 2008 Texas qualifying crash goes into more detail.)

The force a collision produces depends on how long the car takes to stop. Compare the force from your seat belt when you slow down at a stop sign to what you feel if you have to suddenly slam on the brakes.

To give you an idea of how fast collisions can be, the initial wall impact in the crash that killed Dale Earnhardt Sr. lasted only eight-hundredths (0.08) of a second.

SAFER barriers use a car’s kinetic energy to move a heavy steel wall and crush pieces of energy-absorbing foam. That extracts energy from the car, plus the barrier extends the collision time.

The disadvantage is that a car with lower kinetic energy won’t move the barrier. Then it’s just like running into a solid wall.

That’s the same problem the Next Gen car seems to have.

Chassis stiffness: A Goldilocks problem

The Next Gen chassis is a five-piece, bolt-together car skeleton, as shown below.

A graphic showing the five parts of the Next Gen chassis.
Graphic courtesy of NASCAR. Click to enlarge.
The foam surrounding the outside of the rear bumper
The purple is energy-absorbing foam. Graphic courtesy of NASCAR. Click for a larger view.

That graphic doesn’t show another important safety feature: the energy absorbing foam that covers the outside of the bumpers. It’s purple in the next diagram.

All cars are designed so that the strongest part of the car surrounds the occupants. Race cars are no different.

The center section of the Next Gen chassis is made from stout steel tubing and sheet metal. Components become progressively weaker as you move away from the cockpit. The bumper, for example, is made of aluminum alloy rather than steel. The goal is transforming all the kinetic energy before it reaches the driver.

Because the Next Gen car issues are with rear impacts, I’ve expanded and highlighted the last two pieces of the chassis.

The rear clip and bumper, with the fuel cell and struts shaded

The bumper and the rear clip don’t break easily enough. The rear ends of Gen-6 cars were much more damaged than the Next Gen car after similar impacts.

If your initial thought is “Just weaken the struts,” you’ve got good instincts. However, there are two challenges.

I highlighted the first one in red: the fuel cell. About the only thing worse than a hard collision is a hard collision and a fire.

The other challenge is that a chassis is a holistic structure: It’s not like each piece does one thing independent of all the other pieces. Changing one element to help soften rear collisions might make other types of collisions harder.

Chassis are so complex that engineers must use finite-element-analysis computer programs to predict their behavior. These programs are analogous to (and just as complicated as) the computational fluid dynamics programs aerodynamicists use.

Progress takes time

An under-discussed complication was noted by John Patalak, managing director of safety engineering for NASCAR. He told NBC Sports’ Dustin Long in July that he was surprised by the rear-end crash stiffness.

The Next Gen car’s crash data looked similar to that from the Gen-6 car, but the data didn’t match the drivers’ experiences. Before addressing the car, his team had to understand the disparity in the two sets of data.

They performed a real-world crash test on a new configuration Wednesday. These tests are complex and expensive: You don’t do them until you’re pretty confident what you’ve changed will make a significant difference.

But even if the test goes exactly as predicted, they aren’t done.

Safety is a moving target.

And always will be.

NASCAR weekend schedule for Charlotte Motor Speedway Roval

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NASCAR Cup Series drivers race on the road for the final time this season Sunday, as the Charlotte Motor Speedway Roval course ends the playoffs’ Round of 12.

The 17-turn, 2.28-mile course incorporating the CMS oval and infield will determine the eight drivers who will advance to the next round of the playoffs. Chase Elliott won last Sunday at Talladega Superspeedway and is the only driver who has qualified for a spot in the Round of 8.

Entering Sunday’s race, Austin Cindric, William Byron, Christopher Bell and Alex Bowman are below the playoff cutline. Bowman will not qualify for the next round because he is sidelined by concussion-like symptoms.

The race (2 p.m ET) will be broadcast by NBC.

Charlotte Motor Speedway Roval (Cup and Xfinity)

Weekend weather

Friday: Sunny. High of 81 with a 6% chance of rain.

Saturday: Mixed clouds and sun. High of 67 with a 3% chance of rain.

Sunday: Sunny. High of 68 with a 3% chance of rain.

Friday, Oct. 7

(All times Eastern)

Garage open

  • 12 – 5 p.m. — Xfinity Series

Saturday, Oct. 8

Garage open

  • 7 a.m. – 2:30 p.m. — Cup Series
  • 8:30 a.m. — Xfinity Series

Track activity

  • 10 – 10:30 a.m. — Xfinity practice (NBC Sports App)
  • 10:30 – 11:30 a.m. — Xfinity qualifying (NBC Sports App)
  • 12 – 1 p.m. — Cup practice (NBC Sports App, USA Network coverage begins at 12:30 p.m.)
  • 1 – 2 p.m. — Cup qualifying (USA Network, NBC Sports App)
  • 3 p.m. — Xfinity race (67 laps, 155.44 miles; NBC, Peacock, Performance Racing Network, SiriusXM NASCAR Radio)

Sunday, Oct. 9

Garage open

  • 11 a.m. — Cup Series

Track activity

  • 2 p.m. — Cup race (109 laps, 252.88 miles; NBC, Performance Racing Network, SiriusXM NASCAR Radio)

 

Rodney Childers fined $100,000, suspended for four races

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NASCAR has suspended Rodney Childers, Kevin Harvick‘s crew chief, for four races and fined him $100,000 for what the sanctioning body called modification of a part supplied by a vendor.

The team was penalized for a modification to the deck lid.

Harvick, who is out of the Cup Series playoffs, and the Stewart-Haas Racing No. 4 team were docked 100 points.

Harvick’s car and that of Martin Truex Jr. were taken to NASCAR’s Research and Development Center in Concord, N.C. after last Sunday’s race at Talladega Superspeedway. There were no penalties assessed to the Truex team.

Harvick has been particularly critical of the Next Gen car in recent months, once referring to the “crappy-ass parts” provided by suppliers.

Harvick’s car erupted in flames during the Southern 500 Sept. 4 at Darlington Raceway. After he climbed from the smoking car, Harvick blamed the fire on “just crappy parts on the race car like we’ve seen so many times. They haven’t fixed anything. It’s kind of like the safety stuff. We just let it keep going and keep going.

“The car started burning and as it burned the flames started coming through the dash. I ran a couple laps and then as the flame got bigger it started burning stuff up and I think right there you see all the brake fluid that was probably coming out the brakes and part of the brake line, but the fire was coming through the dash.

“What a disaster for no reason. We didn’t touch the wall. We didn’t touch a car, and here we are in the pits with a burned-up car, and we can’t finish the race during the playoffs because of crappy-ass parts.”

MORE: AJ Allmendinger to return to Cup Series in 2023

Unless the team appeals, Childers would miss races at Charlotte, Las Vegas, Homestead and Martinsville and would return for the season finale at Phoenix.

NASCAR president Steve Phelps told the Associated Press that officials have not targeted Harvick. “I would say that’s ridiculous,” he said. “No one has a vendetta against Kevin Harvick or Rodney or anyone at Stewart-Haas Racing.”

On Wednesday afternoon, Harvick tweeted, “Seems strange…” A Childers tweet called the penalty “Shocker…..”.

NASCAR also announced Wednesday it has suspended Young’s Motorsports crew chief Andrew Abbott indefinitely for a behavioral violation during pre-race inspection. He must undergo anger-management training to be reinstated. The team races in the Camping World Truck Series.